A REVIEW OF COLOR SCIENCE AND COLOR AERIAL RECONNAISSANCE

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP88B00592R001402290007-5
• Release Decision: RIFPUB
• Original Classification: C
• Document Page Count: 195
• Document Creation Date: December 21, 2016
• Document Release Date: May 30, 2008
• Sequence Number: 7
• Publication Date: January 1, 1972
• Content Type: REPORT

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CONFIDENTIAL
NATIONAL PHOTOGRAPHIC
INTERPRETATION CENTER
TECHNICAL
PUBLICATION
A REVIEW OF COLOR SCIENCE AND
COLOR AERIAL RECONNAISSANCE
CONFIDENTIAL
NGA Review Complete
GROUP 1 EXCLUDED FROM
AUTOMATIC DOWNGRADING
AND DECLASSIFICATION
NPIC/R-03/72
JANUARY 1972
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This document contains information affecting
the national defense of the United States,
within the meaning of Title IS, sections
793 and 794, of the U.S. Code, as amended.
Its transmission or revelation of its contents
to or receipt by an unauthorized person is
prohibited by law.
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CONFIDENTIAL NPIC/R-03/72
A REVIEW OF COLOR SCIENCE AND
COLOR AERIAL RECONNAISSANCE
January 1972
NATIONAL PHOTOGRAPHIC INTERPRETATION CENTER
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1.0 INTRODUCTION . . . . . . . . ? . . . . . . . . . . . . . . 1
1.1 PURPOSE AND SCOPE . . . . . . .. . .
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2.0 THE PHYSIOLOGICAL AND PSYCHOLOGICAL ASPECTS OF COLOR
VISION . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1 THE ANATOMY AND FUNCTION OF THE VISUAL SYSTEM AS RELATED TO
COLOR . . . . . .
2.2 THE COLOR SENSITIVITY OF THE VISUAL SYSTEM . . . . . . . . 9
2.2.1 Luminous Range . . . . . . . . . . . . . . . . . . . 9
2.2.2 Spectral Range . . . . . . . . . . . . . . . . . . . 11
2.2.3 Geometric Extent of the Color Zones . . . . . . . . 13
2.3 COLOR PERCEPTUAL PHENOMENA
2.3.1 Area Effect . . . . . . . . . . . . . . . . . . . . 16
2.3.2 Simultaneous Contrast and Edge Effects . . . . . . . 17
2.3.3 Spreading Effects . . . . . . . . . . . . . . . . . 19
2.3.4 After Images . . . . . . . . . . . . . . . . . . . . 19
2.3.5 Color Constancy . . . . . . . . . . . . . . . . . . 20
2.3.6 Irradiation . . . . . . . . . . . . . . . . . . . . 21
2.3.6.1 Explanation of Irradiation . . . . . . . . . 21
2.3.6.2 Additional Complications of Mach Bands for
Photointerpretation . . . . . . . . . . . . . 23
2.3.7 Adaptation . . . . . . . . . . . . . . . . . . . . . 24
2.4 DEPTH PERCEPTION AND COLOR . . . . . . . . . . . . . . . . 25
6
2.4.1 Perceptual Cues of Depth . . . . . . . . . . . . . . 25
2.4.1.1 Monocular Cues . . . . . . . . . . . . . . . 25
2.4.1.2 Binocular Cues . . . . . . . . . . . . . . . 26
2.4.2 Effect of Color on Cues . . . . . . . . . . . . . . 28
2.4.3 Chromastereopsis . . . . . . . . . . . . . . . . . . 28
2.4.4 The Pulfrich Phenomenon . . . . . . . . . . . . . . 29
2.5 COLOR CAPABILITIES AND SKILLS . . . . . . . . . . . . . . . 29
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TABLE OF CONTENTS (Continued)
Page
2.5.1 Color Discrimination . . . . . . . . . . . . . . . . . 29
2.5.2 Color Memory . . . . . . . . . . . . . . . . . . . . . 30
2.5.3 Color Naming . . . . . . . . . . . . . . . . . . . . . 32
2.5.4 Color Matching (see also 3.4 COLORIMETRY) . . . . . . 32
2.6.1 Defective Color Vision . . . . . . . . . . . . . . . . 34
2.6.1.1 Types of Color Vision Defects . . . . . . . . . 35
2.6.1.2 Congenital versus Acquired Color-Vision
Defects . . . . . . . . . . . . . . . . . . . . 36
2.6.1.3 The Effects of Age on Color Perception . . . . 36
2.6.2 Color-Vision Tests . . . . . . . . . . . . . . . . . . 37
2.6.2.1 Pseudoisochromatic Chart Tests (PIC) . . . . . 37
2.6.2.2 The Farnsworth-Munsell 100-Hue Test (FMT) . . . 38
2.6.2.3 The Inter-Society Color Council Color Aptitude
Test (ISCC-CAT) . . . . . . . . . . . . . . . . 38
2.6.2.4 The Burnham-Clark-Munsell Color-Memory Test
(BCMS) . . . . . . . . . . . . . . . . . . . . 39
2.6.2.5 Campimeter Test . . . . . . . . . . . . . . . . 40
2.6.2.6 Explanation of Test Battery Usage . . . . . . . 40
2.7 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.0 THE PHYSICS OF COLOR . . . . . . . . . . . . . . . . . . . . 46
3.1 THE PHYSICAL ASPECTS OF COLOR
3.2 THE ADDITIVE AND SUBTRACTIVE CONCEPT OF COLOR REPRODUCTION 53
3.2.1 The Additive Method of Color Reproduction . . . . . . 54
3.2.2 The Subtractive Method of Color Reproduction . . . . . 54
3.3 COLOR SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . 60
3.3.1 Munsell System . . . . . . . . . . . . . . . . . . . . 60
3.3.2 CIE System . . . . . . . . . . . . . . . . . . . . . . 62
3.3.3 Lovibond System . . . . . . . . . . . . . . . . . . . 65
3.3.4 Ostwald System . . . . . . . . . . . . . . . . . . . . 65
3.3.5 DIN System . . . . . . . . . . . . . . . . . . . . . . 67
3.3.6 Densitometric Munsell System . . . . . . . . . . . . . 69
3.3.7 ISCC-NBS System . . . . . . . . . . . . . . . . . . . 69
3.3.8 NuHue, Plochere, Ridgway, Maerz and Paul, Villalobos,
Textile Color Card Association, and Methuin . . . . . 70
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TABLE OF CONTENTS (Continued)
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3.4 COLORIMETRY--THE MEASUREMENT OF COLOR . . . . . . . . . . . . 70
3.4.1 Instrumental Colorimetry . . . . . . . . . . . . . . . 73
3.4.1.1 Recording Spectrophotometer . . . . . . . . 73
3.4.1.2 Tristimulus Colorimeter . . . . . . . . . . 75
3.4.2 Visual Colorimetry . . .. . . . . . . . . . . . . . . . 75
3.4.3 Treatment of Calorimetric Data and Error Analysis . . 77
3.4.4 Metamerism and Metameric Colors . . . . . . . . . . . 78
3.4.5 Color Differences and Tolerances . . . . . . . . . . . 81
3.4.6 Color Rendering and Color-Rendering Indices . . . . . 83
3.5 COLOR DENSITOMETRY . . . . . .. . . . . . . . . . . . . . . . 83
3.5.1 Specular and Diffuse Density . . . . . . . . . . . . . 85
3.5.2 Analytical and Integral Densitometry . . . . . . . . . 85
3.6 REFERENCES . . . . . . . . . .. . . . . . . . . . . . . . . . 89
4.0 COLOR AERIAL PHOTOGRAPHY . . .. . . . . . . . . . . . . . . . 94
4.1 COLOR-FILM THEORY . . . . . . . . . . . . . . . . . . . . . . 94
4.2 PHOTOGRAPHIC PROPERTIES OF SELECTED AERIAL FILMS . . . . . . 99
4.2.1 Color Films . . . . . . . . . . . . . . . . . . . . . 99
4.2.2 False-Color Films . . . . . . . . . . . . . . . . . 101
4.2.3 Spectrazonal or Multispectral Film and Techniques . . 102
4.2.4 Additive Color Separations . . . . . . . . . . . . . . 103
4.3 EFFECTS OF TARGET AND ACQUISITION PARAMETERS ON COLOR AERIAL
PHOTOGRAPHY AND COLOR PERCEPTION . . . . . . . . . . . . . . 103
4.3.1 Colorimetric Properties of Selected Natural and Man-
Made Targets . . . . . . . . . . . . . . . . . . . . . 103
4.3.2 Effects of the Atmosphere and Sun Angle . . . . . . . 108
4.3.3 Effects of Lenses and Lens Aberrations . . . . . . . . 114
4.3.4 Effects of Platform and Camera Vibration . . . . . . . 114
4.4 EFFECTS OF FILM AND PROCESSING PARAMETERS ON COLOR AERIAL
PHOTOGRAPHY AND COLOR PERCEPTION . . . . . . . . . . . . . . 114
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TABLE OF CONTENTS (Continued)
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4.4.1 Effects of Granularity . . . . . . . . . . . . . . . . 114
4.4.2 Effects of Film Variance . . . . . . . . . . . . . . . 115
4.4.3 Effects of Processing Variance . . . . . . . . . . . . 116
4.5 REFERENCES . . . . . . . . . . . . . . . ... . . . . . . . . 117
5.0 APPLIED ASPECTS OF COLOR AND COLOR PERCEPTION IN IMAGE
INTERPRETATION . . . . . . . . . . . . . . . . . . . . . . . 121
5.1 INTERPRETATION OF COLOR FILMS . . . . . . . . . . . . . . . . 121
5.1.1 Theoretical Advantages of Color Films . . . . . . . . 122
5.1.2 Experimental Comparisons of Color Films With Black
and White Films . . . . . . . . . . . . . . . . . . . 123
5.1.3 Operational Findings on Color Film and Color-Imaging
Techniques . . . . . . . . . . . . . . . . . . . . . . 123
5.1.3.1 Natural Color Films (see 4.2.1 Color Films) . . 124
5.1.3.1.1 Advantages . . . . . . . . . . . . . . . 124
5.1.3.1.2 Disadvantages . . . . . . . . . . . . . 125
5.1.3.2 Color Infrared Film (Ektachrome Infrared 8443,
See 4.2.2 False-Color Films) . . . . . . . . . 126
5.1.3.2.1 Advantages . . . . . . . . . . . . . . . 126
5.1.3.2.2 Disadvantages . . . . . . . . . . . . . 127
5.1.3.3 Additive Color Separation (See 4.4.2 Additive
Color Separations) . . . . . . . . . . . . . . 127
5.1.3.3.1 Advantages . . . . . . . . . . . . . . . 127
5.1.3.3.2 Disadvantages . . . . . . . . . . . . . 128
5.1.3.4 Spectrazonal or Multispectral Techniques (See
4.2.3 Spectrazonal or Multispectral Film and
Techniques) . . . . . . . . . . . . . . . . . . 129
5.1.3.4.1 Advantages . . . . . . . . . . . . . . . 129
5.1.3.4.2 Disadvantages . . . . 129
5.1.3.5 Black and White Infrared (Kodak Infrared
Aerographic Film, See 4.2.4 False-Color
Films) . . . . . . . . . . . . . . . . . . . . 130
5.1.3.5.1 Advantages . . . . . . . . . . . . . . . 130
5.1.3.5.2 Disadvantages . . . . . . . . . . . . . 130
5.1.4 Operational Findings on the Interpretation of Targets
and Backgrounds on Color Films . . . . . . . . . . . . 130
5.1.4.1 Tactical Targets . . . . . . . . . . . . . . . 131
5.1.4.2 Strategic Targets . . . . . . . . . . . . . . 132
5.1.4.3 Cultural Objects . . . . . . . . . . . . . . . 133
5.1.4.4 Vegetation Types . . . . . . . . . . . . . . . 133
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TABLE OF CONTENTS (Continued)
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5.1.4.5 Soils . . . . . . . . . . . . . . . . . . . . . . 134
5.1.4.6 Water . . . . . . . . . . . . . . . . . . . . . 134
5.1.4.7 Geologic Features . . . . . . . . . . . . . . . 138
5.2 THE MENSURATION OF COLOR FILMS . . . . . . . . . . . . . . . 138
5.3 INTERPRETATION TECHNIQUES AND COLOR FILMS . . . . . . . . . . 139
5.3.1 Stereoscopic Viewing . . . . . . . . . . . . . . . . . 139
5.3.2 Magnification . . . . . . . . . . . . . . . . . . . . 139
5.3.3 Scanning Strategies . . . . . . . . . . . . . . . . . 140
5.3.4 Multisensor Viewing . . . . . . . . . . . . . . . . . 140
5.3.5 Change Detection . . . . . . . . . . . . . . . . . . . 140
5.3.6 Reporting Strategies . . . . . . . . . . . . . . . . . 141
5.4 ENHANCING THE INTERPRETATION OF COLOR FILMS . . . . . . . . . 143
5.4.1 Enhancement During Acquisition . . . . . . . . . . . . 143
5.4.1.1 Haze Filters . . . . . . . . . . . . . . . . . 143
5.4.1.2 Antivignetting Filters . . . . . . . . . . . . 143
5.4.1.3 Narrow-Band Filters . . . . . . . . . . . . . . 144
5.4.2 Enhancement During Processing . . . . . . . . . . . . 144
5.4.2.1 Color Separation Negatives . . . . . . . . . . 144
5.4.2.2 Color Balance . . . . . . . . . . . . . . . . . 144
5.4.3 Enhancement During Interpretation . . . . . . . . . . 144
5.4.3.1 Color Filters . . . . . . . . . . . . . . . . . 145
5.4.3.2 Colored Lights . . . . . . . . . . . . . . . . 145
5.5 ILLUMINATION CONDITIONS AFFECTING THE PERCEPTION OF COLOR
IMAGERY . . . . . . . . . . . . . . . . . . . . . . . . . . 145
5.5.1 Illuminant Specifications for Light Tables . . . . . . 145
5.5.1.1 Intensity . . . . . . . . . . . . . . . . . . . 145
5.5.1.2 Spectral Distribution . . . . . . . . . . . . . 146
5.5.2 Illuminant Specifications for Ambient Lighting . . . . 146
5.6 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . 147
6.0 GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . 156
7.0 SUGGESTED READINGS . . . . . . . . . . . . . . . . . . . . . 162
7.1 GENERAL REFERENCES . . . . . . . . . . . . . . . . . . . . . 162
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TABLE OF CONTENTS (Continued)
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7.2 ANATOMY AND PHYSIOLOGY OF COLOR VISION . . . . . . . . . . . 163
7.3 PSYCHOLOGICAL AND PSYCHOPHYSICAL ASPECTS OF COLOR VISION . 164
7.4 COLOR VISION TESTS . . . . . . . . . . . . . . . . . . . . . 165
7.5 PHYSICS OF COLOR . . . . . . . . . . . . . . . . . . . . . . 166
7.6 COLOR SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . 167
7.7 COLORIMETRY AND COLOR DENSITOMETRY . . . . . . . . . . . . . 168
7.8 COLOR AERIAL RECONNAISSANCE . . . . . . . . . . . . . . . . . 169
8.0 INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
FIGURE 2.1 HORIZONTAL SECTION OF THE EYE . . . . . . . . . . . . 5
FIGURE 2.2 THE STRUCTURE OF THE HUMAN RETINA . . . . . . . . . . 7
FIGURE 2.3 THE COURSE OF VISUAL STIMULI AND THE CORRESPONDING
FIELDS OF VISION . . . . . . . . . . . . . . . . . . . 8
FIGURE 2.4 DISTRIBUTION OF THE FOVEAL PHOTOCHROMATIC INTERVAL . . 10
FIGURE 2.5 BEZOLD-BRUCKE PHENOMENON . . . . . . . . . . . . . . . 11
FIGURE 2.6 PHOTOPIC LUMINOSITY FUNCTION (solid line) . . . . . . 14
FIGURE 2.7 THE GEOMETRIC COLOR ZONES OF THE EYE . . . . . . . . . 15
FIGURE 2.8 SIMULTANEOUS COLOR CONTRAST . . . . . . . . . . . . . 18
FIGURE 2.9 BRIGHTNESS CONTRAST . . . . . . . . . . . . . . . . . 18
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LIST OF FIGURES (Continued)
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FIGURE 2.10 ILLUSTRATION OF THE PHENOMENON OF MACH BANDS . . . . 22
FIGURE 2.11 ILLUSTRATION OF DEPTH PERCEPTION AND RETINAL
DISPARITY . . . . . . . . . . . . . . . . . . . . 27
FIGURE 2.12 NUMBER OF JUST-PERCEPTIBLE STEPS BETWEEN NEUTRAL
AND THE SPECTRUM COLORS . . . . . . . . . . . . . . . 31
FIGURE 2.13 DIFFERENTIAL COLOR SENSITIVITY . . . . . . . . . . . 31
FIGURE 3.1 THE ESSENTIAL ELEMENTS OF COLOR . . . . . . . . . . . 47
FIGURE 3.2 THE ELECTROMAGNETIC SPECTRUM . . . . . . . . . . . . 48
FIGURE 3.3 THE SPECTRAL ENERGY DISTRIBUTION FOR A 40-WATT
INCANDESCENT LAMP . . . . . . . . . . . . . . . . . . 49
FIGURE 3.4 THE SPECTRAL ENERGY DISTRIBUTION FOR A 40-WATT
DAYLIGHT FLUORESCENT LAMP . . . . . . . . . . . . . . 49
FIGURE 3.5 THE SPECTRAL ENERGY DISTRIBUTION OF THE LIGHT
REACHING THE OBSERVER'S EYE . . . . . . . . . . . . . 51
FIGURE 3.6 THE COLOR STIMULUS EXPERIENCED BY THE OBSERVER . . . 52
FIGURE 3.7 ADDITIVE COLOR PHOTOGRAPHY - TAKING THE PICTURE . . . 55
FIGURE 3.8 ADDITIVE COLOR PHOTOGRAPHY - RECONSTRUCTING THE
PICTURE . . . . . . . . . . . . . . . . . . . . . . . 56
FIGURE 3.9 SPECTRAL TRANSMITTANCE CURVES FOR IDEALIZED CYAN,
MAGENTA, AND YELLOW DYES . . . . . . . . . . . . . . 57
FIGURE 3.10 A COLOR REVERSAL PHOTOGRAPHIC PROCESS . . . . . . . . 59
FIGURE 3.11 THE CONCEPT OF THE MUNSELL COLOR SYSTEM . . . . . . . 61
FIGURE 3.12 THE CIE COLOR SYSTEM . . . . . . . . . . . . . . . . 63
FIGURE 3.13 THE OSTWALD COLOR SYSTEM . . . . . . . . . . . . . . 66
FIGURE 3.14 THE LINES OF CONSTANT DIN-FARBTON AND DIN-SXTTIGUNG
PLOTTED ON A 1931 CIE DIAGRAM . . . . . . . . . . . . 68
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LIST OF FIGURES (Continued)
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FIGURE 3.15 THE ISCC-NBS HUE NAMES AND ABBREVIATIONS FOR A
CONSTANT MUNSELL VALUE OF SIX . . . . . . . . . . . . 71
FIGURE 3.16 THE ISCC-NBS MODIFIERS FOR A PURPLE,HUE . . . . . . . 72
FIGURE 3.17 A SCHEMATIC DIAGRAM OF A SPECTROPHOTOMETER BEING
USED TO MEASURE THE SPECTRAL TRANSMITTANCE OF A
SAMPLE . . . . . . . . . . . . . . . . . . . . . . . 74
FIGURE 3.19 THE SPECTRAL REFLECTANCE CURVES FOR A METAMERIC PAIR
OF COLORS . . . . . . . . . . . . . . . . . . . . . . 79
FIGURE 3.20 THE SPECTRAL ENERGY DISTRIBUTIONS FOR THE CIE
STANDARD SOURCES A AND C . . . . . . . . . . . . . . 79
FIGURE 3.21 THE SHIFT IN THE CIE CHROMATICITY COORDINATES OF A
PAIR OF METAMERIC COLORS PRODUCED BY CHANGING FROM
CIE STANDARD SOURCE C TO CIE STANDARD SOURCE A . . . 80
FIGURE 3.22 THE STANDARD DEVIATIONS OF COLOR MATCHES BY OBSERVER
PGN, ENLARGED TEN TIMES ON THE 1931 CIE x, y
CHROMATICITY DIAGRAM . . . . . . . . . . . . . . . . 82
FIGURE 3.23 A SCHEMATIC DIAGRAM OF A TYPICAL COLOR DENSITOMETER . 84
FIGURE 4.1 THE CONFIGURATION OF A TYPICAL COLOR FILM . . . . . . 95
FIGURE 4.2 THE FORMATION AND DEVELOPMENT OF A COLORED IMAGE IN
A COLOR-REVERSAL PHOTOGRAPHIC PROCESS . . . . . . . . 97
FIGURE 4.3 CIE CHROMATICITY COORDINATES FOR SELECTED NATURAL
AND MAN-MADE TARGETS . . . . . . . . . . . . . . . . 104
FIGURE 4.4 IMAGE DISTORTION CAUSED BY A TURBULENT ATMOSPHERE . . 109
FIGURE 4.5 LIGHT LOSSES CAUSED BY BOTH ABSORPTION AND SCATTERING
IN THE ATMOSPHERE . . . . . . . . . . . . . . . . . . 111
FIGURE 4.6 DIAGRAM OF THE SUN ANGLE OR SOLAR ALTITUDE AND THE
RELATIVE POSITIONS OF THE EARTH, CAMERA PLATFORM,
AND THE SUN . . . . . . . . . . . . . . . . . . . . . 112
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LIST OF FIGURES (Continued)
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FIGURE 4.7 VARIATION OF TARGET ILLUMINANCE AS A FUNCTION OF
SUN ANGLE . . . . . . . . . . . . . . . . . . . . . . 113
TABLE 4.1 THE PHOTOGRAPHIC CHARACTERISTICS OF SELECTED AERIAL
COLOR FILMS . . . . . . . . . . . . . . . . . . . . . . 100
TABLE 4.2 THE CIE CHROMATICITY COORDINATES, LIGHTNESSES,
DOMINANT WAVELENGTHS AND EXCITATION PURITIES FOR THE
COLORS OF SELECTED NATURAL AND CULTURAL TARGETS . . . . 105
TABLE 4.3 THE MUNSELL AND ISCC-NBC DESIGNATIONS FOR THE COLORS
OF SELECTED NATURAL AND CULTURAL TARGETS . . . . . . . 107
TABLE 5.2 SOILS OF THE LAC BEVIN BASIN AND THEIR MUNSELL VALUES . 142
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This review attempts to explain in simple, understandable lan-
guage the current state of the art of color science and color photography
as it relates to high-altitude aerial reconnaissance, and the Center's
activities. The review provides the Center with a reference (a) for use
by the Center personnel in learning and understanding basic color concepts
and technologies (it is not intended to be a textbook or a handbook),
(b) to show how color will affect the Center, and (c) to show how color will
be used by the Center. For maximum usefulness to the Center, several
criteria were used to guide and limit the compilation and writing of the
review:
(1) The material included in the review should be
relevant and applicable to the Center's activities
and needs. The Center's activity is broad and many
technical disciplines are represented. Thus the
review is broad in scope, covering the psychology,
physiology, and physics of color; color photography;
and applied aspects of color imagery and
interpretation . Materials within these broad
categories, that were unrelated to the Center's activ-
ities are not included. Thus, the reader should not
expect to find a complete and comprehensive review.
(2) The language (terms and concepts) of the review
should be nontheoretical and easy to understand
so that a wide range of Center personnel can read
and understand the material included. For those
who wish or need to know technical detail and
theory, a number of excellent references in all
technical areas are suggested in the report.
(3)
The material should be presented. in a straight-
forward, concise manner so that extraneous words
and concepts would not have to be read.
(4)
The material presented
possible and based on
proven evidence.
should be as up-to-date as
sound empirical or operationally
* The classified information in this topic area is included in the report
entitled "A Review of Color Science and Color Aerial Reconnaissance: An
Addendum".
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(5) The material should be easily accessed. (To
satisfy this criteria, numbered headings are
used extensively and an index is included.) It
should be noted that, as a result, the review is
not an integrated whole, rather many sections
stand alone. Cross-referencing between sections
is used to help the reader gain a fuller under-
standing of the material, in the review, pertaining
to a particular topic area.
To help satisfy these criteria the writers first performed a
comprehensive literature review. Then, individuals working or researching
in certain color-related fields were contacted to gather state of the art
information. Every attempt has been made to avoid the use of unnecessary
technical jargon, lengthy explanations, theoretical considerations, and
yet, to give the reader an understanding of the basic terminologies and
concepts used in color science and aerial photography.
This review begins with the physiology and psychology of color
vision, which is followed by the physics of color. Color aerial photography
is discussed, and the body of the rev-Lew ends with the applied aspects of
color imagery and its interpretation. At the end of each major section is
a partial list of references that are considered the most relevant and
useful for the review.
Within each section, the format of the sections varies to suit the
material presented. In general, the format is continuous and explanatory,
but in the last section dealing with applied aspects much of the information
was disjointed and, thus, is presented in a more discrete fashion.
To help the reader, a glossary and an index are included, and,
within the body of the review, the glossary-defined words are capitalized
and underlined. Important words, defined in the text are also capitalized.
In addition, a suggested reading list has been included for the reader to
find more detailed and theoretical discussions. This reading list is
categorized by topic and level of technical difficulty.
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2.0 THE PHYSIOLOGICAL AND PSYCHOLOGICAL
ASPECTS OF COLOR VISION
The influx of color imagery into the Center's operation will have
at least one fundamental effect; eventually everyone will look at it (as
transparencies or prints). The interpreters, printers, photogrammetrists,
and audiences of briefings will be seeing color imagery. However, these
people may not perceive color in the same way. Where some people see red,
others may see orange. An interpreter viewing color imagery through a
stereoscope will see colors differently than when he views without the
scope. These are but a few examples of many problems which can be
anticipated. The importance of these problems to the Center's activities
and tasks is difficult to anticipate.
2.1 THE ANATOMY AND FUNCTION OF THE VISUAL
SYSTEM AS RELATED TO COLOR
A complete explanation of the physiological basis of color
perception cannot be given by the present state of the art. Certain facts
are known as to the necessary constituent elements, but how they interact
to achieve color vision can be explained only by theories that are partially
contradicatory.
The purpose of the eye is to focus light rays onto the retina
(the light sensitive layer of the eye) and to convert these rays from light
energy into electrical-like impulses for transmission by the nervous system.
The characteristics of the scene can then be passed up to the interpretative
centers of the brain. Further, these characteristics must be coded in some
way as to their spatial relationships, color, shades, contrast, etc. To
do this, the eyes must be able to move, to focus, and to adapt to
fluctuating illumination levels, as a coordinated pair.
The ability of the eyes to move and point specifically at an
object is a part of the basis for the relatively high resolution ability
of the visual system, because good acuity as well as good color discrim-
ination is concentrated in the central part of the visual field. Very
rapid and precise movements of the eyes in mutual coordination are made
possible by a set of three pairs of muscles attached to the outside of
each eyeball. These muscles move the eye in all directions.
Another set of muscles controls the lids, which in turn protect
and lubricate the exposed surfaces of the eye. An added function of lid
closure is as a part of the light adaptation process, i.e., the partial or
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complete closure of the lids is one way to regulate the amount of light
entering the eye, e.g., squinting in the presence of bright lights.
The external shape of the eyeball is best described as that of
two intersecting spheres - a small transparent one in the front and a
large opaque one in the rear (see Figure 2.1). The front sphere, the
CORNEA, holds a continually changing transparent fluid called the AQUEOUS
HUMOR. The wall of the larger sphere has three specific layers: a tough
light-proof outer protective coat, the SCLERA; a highly vascularized*
nutrient layer, the CHOROID; and an innermost layer of complex and delicate
nervous tissue called the RETINA. Within this sphere is a transparent gel,
the VITREOUS HUMOR. Separating the two spheres is a curtain-like structure,
the IRIS, with a slightly decentered** opening called the PUPIL. The size
of this opening is continually changing due to the effects of illumination-
level changes and other stimulus conditions. This control of the light
level is also a part of the adaptation process of the eye. Directly in
back of the iris and in the rear chamber is a small flexible transparent
structure (the LENS). Its purpose is to vary the focal length of the eye
to form a clear or focused image on the retina as the gaze is shifted to
objects at different viewing distances. Muscular action by a structure
surrounding the lens, the CILIARY BODY, exerts a force on the lens causing
it to change shape and, hence, to alter its focal power. The alteration,
known as the ACCOMODATION process (or focusing), is very important to
the maintenance of clear imagery in the eye. Focusing ability declines
with age--most people become far-sighted with age. These transparent struc-
tures, the cornea, the aqueous humor, the lens, and the vitreous humor,
comprise the focusing apparatus of the eye. Most of the focusing power of
the eye is attributable to the cornea., The lens varies in shape and, hence,
optical or focusing power, to permit the position of the image formed by
the optics of the eye to fall on the retina.
The innermost layer of the eye, the retina, is composed of
nervous and supporting connective tissue, and it is structurally and
functionally a forward extension of the brain. It spreads laterally over
the entire inner surface at the back of the eyeball. However, its detail
discrimination ability and color sensation are clustered in the MACULAR
area, a depression in the retina, (see Figure 2.1) situated at the extreme
rear of the eye. Further, these abilities are strongest at the apex of
the macula known as the FOVEA CENTRALIS. The optical quality of the image
formed is also better at this point than anywhere else on the retinal
* The choroid may also be thought of as an extremely dense mass of tiny
blood vessels.
** This decentration is a partial basis for a little known illusion.
(see Chromastereopsis, Section 2.4.3) that may have a bearing on the
photointerpretation task.
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Sclera
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surface. The periphery of the retina does not have good discrimination for
either detail or color. Its greater sensitivity to light, than that of the
central retina, is achieved by adding weak signals from a wide area.
Primarily, the peripheral retina is an aid in locating objects and in
minimizing orientation, both of which must be understood as a part of the
total visual process.
The radial or in-depth arrangement of the retina with its 10
well-defined microscopic layers, must be considered. The functional
structure is "turned inside out", because the light must pass through the
entire retinal structure before striking the light-sensitive or photo-
receptive layer of the retina made up of the RODS and CONES (see Figure 2.2).
In the rods and cones the light energy is absorbed and initiates chemical
changes. The resulting "coded" electrical impulses flow along nerve fibers
toward the center of the eye, traveling across a series of three types of
nerve cells. The junctions between these nerve cells are known as
SYNAPSES. At this stage, indeed even before it has left the eye, the
signal is in the initial stages of interpretative processing by the brain.
The prevailing opinion as to the character of the cones and their
geometric arrangement is that there are three separate types of cones, each
maximally sensitive to a wavelength in the red, green, or blue spectral
region. The cones are situated side by side, possibly randomly and
possibly clustered to a certain extent, but all at the same depth. The
mechanism for the separation of the light energies into color is not well
known, other than that it is a function of the cones. The function of
the rods has nothing to do with discrimination of colors.
The innermost layer of the retina, the GANGLION FIBER (see
Figure 2.2) layer, converges from all lateral directions of the retina to
a central exit point, the OPTIC DISC or BLIND SPOT. Here, all of the
impulses leave the eye in a flexible cable-like structure, the OPTIC NERVE.
The area of the optic nerve exit, since it has no rods or cones (the
light receptors), is a true blind spot. The individual is unaware of this,
because of two filling-in processes; one, a "mental" process and the other
an overlapping by the corresponding image from the other eye. It is
possible, however, that with prolonged staring with one eye (with the other
eye covered or not being used for some reason) an object could be "lost"
because its ocular image was focused on the blind spot.
After leaving the eye, the optic nerves from the two eyes
converge in an "X" shaped intersection, (see Figure 2.3) where half of the
fibers within the nerve cross to the opposite side and half do not. The
bundles of nerve fibers after this crossing are the OPTIC TRACTS. Thus,
the fibers from the nasal side of the retina of each eye join with the
temporal fibers from the retina of the other eye. All of the fibers from
one side of the visual field go to one side of the brain. The individual
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Direction of
impulses
Direction of
light
FIGURE 2.2 THE STRUCTURE OF THE HUMAN RETINA. 1, Pigment layer;
2, Rod and cone layer; 3, Synapses; 4, Bipolar cells;
5, Synapses; 6, Ganglion cells; 7. Optic nerve
fibers. After Cady, F. E., and Dates, H. B.,
Illuminating Engineering, New York; John Wiley & Sons,
Inc. 1928 (2nd Ed.), p. 233.
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At, Eyeball
-Optic nerve
Optic tract
Chiasma
!- f ~=-- Gptic radiations
Geniculate body
J )
FIGURE 2.3 THE COURSE OF VISUAL STIMULI AND THE
CORRESPONDING FIELDS OF VISION.
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fibers contained in the optic tract at this point are the ganglion cell
layer fibers from the eyeball. Some now branch off to the SUPERIOR
COLLICULUS, but the majority go on to the region of the LATERAL GENICULATE
BODY, a region of numerous synapses that constitute the first switching gap
after the_eye. From the LATERAL GENICULATE, new nerve fibers, the OPTIC
RADIATIONS, carry derivatives of the original signals from the retinal layer
to the VISUAL CORTEX of the brain, at which point there is presumably some
form of spatial analogue of the viewer's world.
2.2 THE COLOR SENSITIVITY OF THE VISUAL SYSTEM
In a very strict physical sense, color does not exist. Color is
an interpretation of the observer's visual impressions of an object or
light source primarily related to the combinations of wavelengths of light
energy being transmitted (as in a color image), reflected, or generated.
As it happens, most people have similar interpretations, and, thus, color
interpretations can be thought of as a common experience. People whose
color discriminations and descriptions indicate the existence of very
similar color vision are called COLOR NORMAL. The range of light
intensities and colors that the color-normal eye is sensitive to are
described below.
2.2.1 Luminous Range
Although detection of the presence of light is possible at
brightnesses as low as 10-6 cd/m2*, this is too dim for recognizing hue
differences between (or within the area of) light sources. Such
discriminations of hue difference do not begin until light intensities
exceed 10-3 cd/m2.
The first hue to be discriminated with an increase of intensity
is red. (It also disappears last when luminance is decreased.) As
luminance is increased, more colors gradually become distinguishable from
each other, but not at the same time, i.e., light levels. Thus, there are
two thresholds; the lower is the detection of the source as a light, and
the higher is the identification of the source as a hue. The difference
between the two thresholds is known as the PHOTOCHROMATIC INTERVAL.
However, there is a separate value for each color. The graphical
distribution of these values is shown in Figure 2.4.
* Candelas per square meter.
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440 s5Q S20 ?CO 500 s90
Wavelength, nanometers
FIGURE 2.4 DISTRIBUTION OF THE FOVEAL PHOTOCHROMATIC
INTERVAL.
If the luminance continues to be raised, color eventually loses
its purity or saturation, i.e., begins to wash out. Well below the level
of this wash-out effect, a phenomenon known as the BEZOLD-BRLJCKE EFFECT
occurs. This is a perceived hue change (without an accompanying change in
physical wavelength) with increasing luminance. The graph of this effect
is shown in Figure 2.5. Note that the. red-yellows and the green-yellows
become yellower, and the red-blues and. the green-blues become bluer.
However, certain hues tend to remain constant or INVARIANT. In some
instances, these are given as three distinct wavelengths and in others as
four (Committee on Colorimetry, 1953). The former grouping is 478, 505,
and 573 nanometers while the latter has been given as 474, 494 (complement),
506, and 571 nanometers. These are similar to but slightly different from
the psychological primary hues (see below). They are also similar to and
possibly related to the stable or INVARIABLE HUES, a phenomena related to
the unchanging perception of a single hue as it falls on different parts
of the retina (see 2.2.3 Geometric Extent of the Color Zones).
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625 600 550 525 G B 450
i
(Ti 675 650
r-1 00
Wavelength, nanometers
2.2.2 Spectral Range
00
~- -
-
20
1
L
f -
~
,
675 650 625 600 575 550 525 SOO 475 4;
FIGURE 2.5 BEZOLD-BRUCKE PHENOMENON.
The normal eye is sensitive to colors of wavelengths ranging from
about 380 to 770 nanometers. However, at the extreme ends of this range the
sensitivity to light energy is extremely low, i.e., the visual thresholds
are very high. Consequently, the range is usually given as a working
figure of 400-700 nanometers. This range of visual sensitivities makes up
the VISUAL SPECTRUM, a very small part of the total electromagnetic spectrum
(see 3.1 THE PHYSICAL ASPECTS OF COLOR).
It is within this range that colors are seen and reliably, i.e.,
repeatedly with consistent results interpreted by humans with normal color
vision. According to LeGrand (1968), 250 hues can be distinguished in side
by side comparisons within the spectrum. Halsey and Chapanis (1951) find
that this figure shrinks to about 11 if there is no reference or comparison
chip immediately and simultaneously adjacent. Alternatively, if saturation
and brightness are also allowed to vary, the number of distinguishable
colors may reach into the millions.
Table 2.1 is a breakdown of wavelengths by prevailing or popular
names. These names can be further reduced to those of the psychological
primaries, which Evans (1948) notes as blue, green, yellow, and red. These
primaries have also been called the UNITARY (Judd, 1963) or UNIQUE HUES in
that they seem to have no other contaminating colors. Combinations of
these hues then can be used verbally to describe intermediate hues as in
Table 2.1. Unfortunately, these names lack the precision (freedom from
ambiguity) needed for other than verbal descriptions. Ingling (l971)*, for
example, notes that the blue primary is between 470 and 480 nanometers;
W personal conversation
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TABLE 2.1 WAVELENGTH REGIONS AND HUE NAMES
(Burnham, et al., 1963)
Approximate
Wavelength Region
in nanometers
380-470 Reddish Blue
470-475 Blue
475-480 Grennish Blue
480-485 Blue-Green
485-495 Bluish Green
495-535 Green
535-555 Yellowish Green
555-565 Green-Yellow
565-575 Greenish Yellow
575-580 Yellow
580-585 Reddish Yellow
585-595 Yellow-Red
595-770 Yellowish Red
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green is an ambiguous in that 75-80 percent of the color-normal population
sets unique green at 510 nanometers and the others use 525 nanometers as a
reference. Unique yellow is very sharp and consistent at 580 nanometers.
No one wavelength is consistently identified as red.
The eye is not equally sensitive to all wavelengths, and people
do vary in their sensitivity. Consequently, a statistical composite curve
(the solid line in Figure 2.6) known as the PHOTOPIC or LUMINOSITY CURVE
of the standard observer has been prepared. This shows the statistically
smoothed consensus of human visual sensitivity as a function of wavelength
during daylight or in a well-lighted room. It approximates, but is
unlikely to match, the visual sensitivity of any single individual.
The dashed line in Figure 2.6 represents the composite sensitivity
for vision at night, the SCOTOPIC CURVE. Under dim light conditions,
people are sensitive to colors as shown by the scotopic carve. However,
the colors are not perceived as such, only as shades of gray. Only under
light adapted conditions, i.e., the photopic curve, will colors be perceived.
The brightness boundary line between these two stages is about
0.1 millilambert. Anyone who works with color imagery or prints and must
see colors clearly to judge color fidelity, balance, or to name colors,
must work in a well-lighted area and become light adapted before judging
or naming colors.
2.2.3 Geometric Extent of the Color Zones
The sensitivity of the retina for colors progressively decreases
from the macula to the periphery. Essentially, a point is reached at which
the sensation of color disappears and there is only an awareness of light
or no light. Figure 2.7 is a plot of this information on a polar-coordinate
diagram. The irregular boundary lines connecting all of the points (within
which there is color perception - outside of which there is none) for a
particular color is the ISOPTER for that color. The isopter is a
statistical concept--a guide and not an exact measurement for any single
person. Such isopters are illustrated in Figure 2.7 for the more important
principal colors. Thus, green has the smallest zone, followed by red,
yellow, and blue, respectively. However, people may have varying
individual diagrams, e.g., different sequences of loss or interlacing of
the isopters.
The color zones as measured by the isopters vary in size and
shape for each individual depending on:
(1) State of light or dark adaptation of the retina -
maximum zone size will be the light-adapted state.
Thus, those judging colors must be light-adapted.
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0
400
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I
i
i
I I~
I
I
500 600 700
Wavelength, nanometers
FIGURE 2.6 PHOTOPIC LUMINOSITY FUNCTION (solid line).
Scotopic curve is included for comparison.
From Judd, D. B., Color in Business Science
and Industry, New York: John Wiley & Sons,
Inc., 1952, Frig. 2, p 9.
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FIGURE 2.7 THE GEOMETRIC COLOR ZONES OF THE EYE.
(Committee on Colorimetry, 1953).
NOTE: The concentric circles represent the number of degrees outward (i.e., eccentricity)
and the radial lines represent the direction of this outwardness (the meridians),
also measured in degrees.
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(2) Light intensity - zone sizes will increase with
light-source intensity as long as the source is
below discomfort glare levels. Thus, light
levels should be relatively high for viewing
color imagery or prints.
As can be seen in Figure 2.7, color perception changes as the
point of stimulation increases in angular eccentricity from the fovea. The
hue usually changes. However, with some wavelengths (known as the stable or
INVARIABLE HUES) there is a loss in saturation. There are four such hues
and Zoethout (1947) records them as being 574, 495, and 471 nanometers, and
a nonspectral purplish-red.
The foregoing means that precise color interpretation (matching,
identifying, discrimination, etc.) must be done with central vision.
However, our eyes are continually moving and, consequently, some color
sensitivity is needed in the peripheral area immediately surrounding the
central retina.
Further, peripheral vision is important to the interpreter
during scanning. Clearly from the above data, certain colors will be more
conspicuous in peripheral vision than others. It would appear that, if
lightness and saturation were comparable, predominantly green colors would
be the least conspicuous in peripheral vision.
In viewing a color print or transparency, one may not perceive
colors accurately. This is due to a number of perceptual phenomena
related to color. Interpreters and others at the Center, dealing with
color imagery, should realize the existence of the phenomena, so that some
compensations can be made. How serious the effects of these phenomena
will be on specific tasks is very difficult to determine without further
experimentation and study. These phenomena will most likely occur, but
may not seriously affect the work of an individual.
Variations in the retinal area covered by a colored object can
cause a change in the perceived color. This is called an "area effect".
In general, as the area of an object increases from 0 to about 20 degrees
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on the retina, the saturation and brightness of its color increases, then
with further increases in area it becomes progressively less saturated
(Burnham, et al. 1963). Thus, large objects on an image which are in fact
the same color as smaller ones may appear more or less saturated.
2.3.2 Simultaneous Contrast and Edge Effects
Simultaneous color contrast involves an unrealistic perception
of a color due to the influence of a nearby or surrounding color (called.
the "inducing" color or field). For example, in Figure 2.8, the inner
areas of the two squares are printed with the same ink, but they appear
different in lightness, due to the different surrounding fields. The same
phenomenon occurring with shades of gray (see Figure 2.9), is more properly
known as Brightness Contrast. How colors affect one another is very
complex, since hue, saturation, and brightness may all be involved. In
general, the eye tends to accentuate the differences between colors. If,
for example, two colors (or two groups) differ only in brightness, the
difference appears exaggerated, i.e., the brighter of the two will appear
brighter than in reality and the darker will appear darker. The same holds
true for saturation differences when the hues are nearly the same. Hues
affect one another in complex ways, but, in general, adjacent hues appear
more different in hue than if viewed separately. If the two hues are
nearly COMPLEMENTARY they will generally appear more saturated.
These color contrast effects are most prominent when:
(1) The inducing field is large and the induced
area is small
(2) The inducing field is adjacent to or surrounds
the induced area (maximum effect is at the edge
of adjacent fields)
(3) The inducing field is highly saturated
(4) The brightness contrast is either absent or
reduced.
The effects are reduced by:
(1) The presence of well-defined borders
(2) The presence of texture
(3) The recognition of the induced area as a known object.
17
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To eliminate these effects, when it is necessary to determine the
precise color of an area embedded in other colors, that area should be
brightly illuminated with a standard white light and viewed through an
aperture in a neutral gray background. A reference color, if used, would
need the same background and illumination.
Another important relationship is that sharp contours or edges
(as in a well-focused image) increase the apparent saturation and brightness
of the colors. Fuzzy edges (as in out-of-focus images) tend to reduce
apparent saturation and brightness. These phenomena are known as edge
effects.
2.3.3 Spreading Effects
Burnham, et al. (1963) notes that with certain "complicated"
object situations, made up of patterns of small, spatially close areas,
colors are unrealistically perceived in ways contrary to the principles
of Simultaneous Color Contrast. These perceptual phenomena are known as
Spreading Effects or as Assimilation where adjacent colors appear more
alike than different, as if one color is "spreading" onto the other. For
example, areas surrounded by black lines appear darker than when not
surrounded, or when surrounded by white lines.
2.3.4 After Images
Exposure of the retina to any visual scene or stimulus (colored
or non-colored) is followed by effects known as AFTER IMAGES. After images
are visual responses that occur after direct visual stimulation and appear
as the preceding "true" visual experience decays, i.e., it is a continuance
of the visual scene, but without continuing stimulus. After images are
called positive if the colors or shades of gray duplicate the preceding
visual experience, and negative if the colors or shades of gray are
COMPLEMENTS of the preceding visual experience.
The classic demonstration of a negative after image is to view
an isolated color picture of an object for a prolonged period of time under
good lighting conditions, and then suddenly change the gaze to a well-lit,
untextured white surface. What appears is a fairly clear and well-defined
apparition-like image in the shape of the original object, but with reversed
luminosity and chromaticity, i.e., points in the after image that are now
bright have been dark and vice verse, and the colors are complementary.
The duration of the phenomenon is variable and may last for up to two
minutes.
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One of the problems with an after image is that, while decaying,
it will usually follow the direction of gaze, being superimposed on and
altering the detail, texture and color of the scene currently being viewed.
The resultant color is an approximate mix of the color of the real images
currently being fixated and the color of the superimposed after-image.
Thus, if an interpreter stared at a colored target for a period of time and
then changed his gaze to another scene, the after image would be
superimposed on the next scene and interferes with its perception.
Fortunately, after-image decay is rapid and the problem is seldom of any
consequence.
It is important, however, to minimize the consequences of after
images. Ideally, any viewing should be done under good ambient lighting
conditions, prolonged staring should be minimized, and potential glare
sources in the peripheral field-of-view shielded.
Color constancy is a tendency to perceive colors as approximately
the same colors despite varying illumination and viewing conditions. The
most common example is perceiving snow white in both sunlight and shadow
even though the light reflected from the two areas is quite different.
Another simple example is the apple usually perceived as red whether in
sunlight, skylight, or indoor illumination.
A more relevant but different example is the situation in which
an interpreter reports U. S. military vehicles on color film as olive-drab,
but in fact the film colors may have a blue tine due to color imbalance.
The explanation is that the interpreter "knows" the color, and the vehicles
evoke a color name in his memory which then affects his perception.
These examples show that known and familiar objects can appear
approximately the same known color under different levels and types of
illumination and viewing conditions. To minimize the effects of color
constancy when the precise color must be determined, color-reference
samples should be used alongside the unknown color sample in question
for immediate, simultaneous, and continuing comparison; and careful
analytical attitude toward color viewing should be maintained.
Color constancy, however, is generally not a hinderance to photo-
interpretation. It is an aid to detection and identification, because it
provides perceptual continuity to objects and scenes.
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Areas or objects of color, which are brighter, i.e., more intense
than their surround, seem to spread or irradiate onto that surround. This
is true whether the color is a light source or transparency. The
phenomenon leads to a very slight enlarging of a light source or area in a
viewed scene. Conversely, a dark object embedded in a bright surround will
appear to contract or be smaller.
Irradiation can be a problem in photointerpretation work since
the photographic density on different exposures of the same scene can vary
and result in one scene being brighter than the others. Targets or areas
may appear slightly larger on the brighter exposure.
2.3.6.1 Explanation of Irradiation
First, irradiation is due to the focusing position of the eye
with respect to the visual spectrum. In white light, the eye is usually
focused for the midpoint of the spectrum, represented by yellow, making the
ends of the spectrum (blue and red) slightly blurred.
This blur is interpreted as a spread. Thus, in white light, with
normal focus for yellow, the observer will see more spread in blue and red
than in yellow. In some instances, e.g., for the near-sighted, the focus
is not for yellow, but tends toward red, changing the amount of blue (or
spreading) for the different colors. Here, the spreading in the blue is
greater than the normal spread when focusing in the yellow. This effect,
as in chromasteropsis (see Section 2.4.3) is a result of the lateral
chromatic aberration of the eye.
Second, spreading is due to what is known as a Mach band
phenomenon. Figure 2.10 is a graph of the emittance or reflectance of
light from two objects (A and B) at their borders with a surround of darker
luminosity. The left side of the abscissa of both A and B represent a
base line,i.e., minimal light from a dark object where the right side
represents the higher light output from a more luminous area. This could
also be taken to be a more luminous object against a darker surround.
The true physical transition represented'by the vertical line in both
cases does not apply to the luminosity distribution when the base line is
spread out. Here, the slope of that spread is representative of the
sharpness of the border. That slope is presented by the solid lines in
both A and B. When there is a significant change in slope, the eye
perceptually tends to emphasize the change, represented by the dotted
line in each case. The more abrupt the change in the true slope (as in
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0
Light Side
Light Side
FIGURE 2.10 ILLUSTRATION OF THE PHENOMENON OF MACH BANDS
(The ordinate in both A and B represents
luminance, and the abscissa is distance to
the left and right of the zero point
representing as closely as possible the
actual physical boundary of the border.
The solid lines are the true luminous
distribution, and the dotted lines represent
the perceived luminous distribution, which
differs from true at the change in slope.
The physical appearance of this difference
is called the Mach Band.)
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B), the more noticeable is the perceptually added emphasis which makes
sharp borders appear to be sharper, and fuzzy borders fuzzier.
The two lines or bands of emphasis (two for every border) in
terms of an image are seen as two "halos" (Mach bands), one dark and the
other light, completely surrounding the border (and hence any object) with
the dark being on the dark side of the distribution and the light being on
the light side. In reality, the bands are often extremely difficult to
see.
When an observer is asked to judge size, or the position of a
border, he does not indicate the midpoint between the bands--corresponding
to the true physical transition point. Instead, he tends to make a
selection closer to the dark band. In this way, dark objects shrink and
bright objects expand.
2.3.6.2 Additional Complications of Mach Bands
for Photointerpretation
Color seems to have an effect on the appearance of Mach. bands.
However, the effect is due to brightness differences rather than chromatic
differences. If two colors with both differences in luminosity and border
sharpness are placed side by side, careful observation discloses, in place
of the expected bright clear border, a bright line or band of the brighter
color on its side of the boundary line. A similar effect will be seen with
the darker color on the darker side.
The perception of these bands differs markedly under microscopic
and macroscopic illumination according to Charman and Watrasiewicz (1964).
Instead of a simple pair, under microscopic examination, they find a
multiple band structure with at least one bright and two dark bands on the
dark side, and a bright band on the high-intensity side. The bands become
more pronounced as the condenser-lens aperture is cut down in size. They
further note that this subjective enhancement may aid in detection and
recognition of small detail. Unfortunately, it will increase the variation
in accuracy of size measurement, and there is a possiblity that the
subjective fringes will be mistaken for fine detail surrounding larger
objects.
Clearly, the presence of color and the variation in the Mach-
band effect under microscopic examination, create additional complications
for consistency of results in photointerpretation and mensuration.
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2.3.7 Adaptation
Adaptation is the process by which the eye makes the necessary
adjustments in its photoreceptive system to correctly and continuously
perceive objects or scenes under changing light characteristics. Adjusting
from a dark to a more lighted environment is called LIGHT ADAPTATION, and
the reverse is called DARK ADAPTATION. In most instances, light adaptation
is adequate within a minute, particularly if the criterion is not overly
demanding. A slightly better level for working purposes is achieved in
2-3 minutes with a very slight additional improvement between 10 and
15 minutes.
Starting from a daylight environment, the initial stages of dark
adaptation are also very fast. It is reduced about a log level, e.g., from
1000 to 100 millilamberts, in a few seconds. After that, depending on the
individual, it can be another 5-10 minutes until the PHOTOPIC visual system
is adapted out and the SCOTOPIC takes over at about 0.1 millilambert.
Darkroom conditions using safelight illumination are still in the low
photopic range (not in the scotopic range, as might be expected), having a
range of between 0.5 and 1.5 millilamberts. When using some extremely
sensitive materials, darkroom conditions may have to go even lower, which
would then be into the scotopic region of human vision. The eye can continue
to dark adapt down into this region, but to reach a "zero" level can often
take over an hour.
Recognition of color is functional only at luminances in excess
of 0.1 millilambert. It will be optimal at between 10 and 100 millilamberts
if it can be assumed that the observer has a 2-millimeter pupil size.
CHROMATIC or COLOR ADAPTATION is the ability of the eye to adjust
its spectral sensitivity. Although the mechanism of color adaptation is
unknown, it is involuntary and is a part of the process of light and dark
adaptation. Thus, as the light in the. visual scene gets dimmer, color
gradually disappears, changing the world into a series of grays. As the
light is increased, a brightness is reached at which the spectral sensitivity
of the retina can optimally perceive colors. Failure to allow adequate time
for light and dark adaptation to occur can lead to false color perceptions.
The important aspect of color adaptation is adaptation to a single
color. If the eyes fixate on a single color (such as a target on color
imagery) for a few seconds, the retina will adapt to the color, i.e., become
less sensitive to it. When the eyes fixate on another color (another target)
that color is not seen correctly. However, in a few seconds the retina
will adapt to the new color. When viewing complex color scenes, however,
this problem may not occur, since there are continual eye movements.
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For critical color judgements and discriminations, the eyes must
be allowed to adjust to each new situation before judgements or decisions
are made, and abrupt changes in illumination must be avoided.
2.4 DEPTH PERCEPTION AND COLOR
One of the keystones upon which the art'and science of photo-
interpretation has been built is the ability to recognize and measure
depth, height, or distance on film. This complex ability is based on many
cues. Such cues are well-known and apply to black and white as well as
color film. At times, the addition of color may vary the effect of the cue,
even to the extent of altering the total perception. When viewing imagery
and trying to form a judgment as to height (or depth), one is usually
unaware of the cues being used i.e., they operate at a subconscious level.
2.4.1 Perceptual Cues of Depth
Cues are of two types, one-eyed or MONOCULAR and two-eyed or
BINOCULAR. There are more monocular cues and they generally apply at
greater viewing distances than do the binocular cues. Monocular cues are
available when using both eyes; binocular cues vanish when only one eye
is used. In photointerpretation of photographs in matched stereoscopic
pairs (each picture of the pair taken from a different location in space),
the binocular cue of stereopsis (see below) can become the single most-
powerful cue to depth perception.
2.4.1.1 Monocular Cues
The important monocular cues are:
(1) Relative Size - The detection of distance (or
depth) depends on the size of the image formed
on the retina of the eye: objects with larger
images, other aspects being equal, appear to be
closer.
(2) Interposition - Overlapping objects are
interpreted as being nearer than the overlapped
objects.
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(3) Linear Perspective - The perception of distance
due to the smaller angular size that objects seem
to have when they are distant as compared to when
those same objects are near, i.e., closer to the
observer , and provided that there is an opportunity
for simultaneous comparison in the one scene.
As a practical matter, the objects may be
different, needing only to be similar in real
size. The usual example of this phenomenon is
of something parallel (the same size) appearing
to converge in the distance, e.g., railroad tracks
or telephone poles.
(4) Aerial Perspective - The failure to discriminate
the surface details of an object means that the
object is too far away to be seen clearly. As
more and more details are lost, the farther away the
object appears, providing other objects in the
scene are clear.
The important binocular cues are:
(1) Convergence - At close working distances, awareness
that the eyes are turned in rather than parallel is
interpreted as the relative nearness of an object.
(2) Stereopsis - The two eyes see the same object from
a slightly different aspect, which means that the
brain must fuse the two views into a single image.
The image difference due to having different points
of view is known as retinal disparity and is
illustrated in Figure 2.11 when imagery appears
closer to the observer, note that the center portions
are pointing inward. The brain interprets the
inward portion as being closer to the viewer. When
imagery is receding from the observer, note that the
center portions are pointing outward. The brain
interprets the outward portion as being farther
away from the viewer. Thus views A together with
B, or D together with 1: can also be thought of as
stereo pairs of C.
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K
1>
In this diagram, C could be interpreted as either a
view of a sawed-off pyramid pointing toward the
observer or the inside of a box. If this were a real
three dimensional object or specially prepared
stereo pair (anaglyphs) representing the slightly
different view as seen from the different points
in space occupied by the two eyes; the left eye,
in the first instance would be processing image "A"
while the right would be occupied with image "B".
In the second instance, where the total perception
was that of the interior of a box, the left eye
would be seeing image "D" and the right, image "E".
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In general, color does not greatly affect depth perception cues.
However, some colors themselves appear closer than others. This has been
called a psychological awareness of depth. There is no agreement as to
which colors appear closer than others (although red has been stated most
often). Which color appears closer probably varies among people and may
also vary according to luminance. This is an illusory, i.e., misleading,
addition of depth to the color image. In a binocular mode where one
expects depth from stereopsis, two problems may occur: (1) depths may be
exaggerated, and (2) objects or areas may appear to have depth solely due
to their color.
2.4.3 Chromastereopsis
Chromastereopsis is a binocular illusion of depth, due to color,
different than the psychological awareness mentioned above. It can occur
when viewing two or more small, highly saturated colored areas or targets
against a homogeneous background, where the targets are of widely
separated wavelengths but close together in space. On complex imagery where
textured backgrounds are most common the illusion may not occur. However,
on imagery where backgrounds are homogeneous, e.g., water, desert, or on
high-altitude photography where the background details and colors blend
together forming near homogeneity, the illusion is more likely to occur.
Observers usually see reds as closer, and blues and greens
farther away. However, some people see the reverse, and reversal of
direction can occur during observation.
This illusion is quite comp=lex and is believed to be caused by
the combined effects of the color dispersion characteristics of the eye's
optical system, as well as the fact that the foveas and pupils are not
centered on the optical axis of the eye.
The most practical solutions to this illusion are alertness on the
part of the interpreter and inspection of a suspected illusion by another
interpreter.
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2.4.4 The Pulfrich Phenomenon
The Pulfrich phenomenon is an illusion of depth that can occur
with paired stereoscopic images either in black and white or color, when
one of the pair is brighter than the other due to density differences, or
due to a split light-table where one of the pair is given more rear lighting
than the other side. In this phenomenon, the darker of the two retinal
images is perceived as farther away. Thus, one of the two views is
perceived as farther away than the other, and depth may be exaggerated or
stretched causing interpretation and measurement errors. Further research
is required on the Pulfrich phenomenon to determine the effects of the
stereoscopic depth illusion in color photographs. This is particularly so
because the Center is using split light-tables where one eye can obtain
more illumination than the other.
With the advent of color imagery at the Center, it is important
to understand the color capabilities, skills, and limitations of the
average individual. Certainly, anyone at the Center who will be working
with color imagery (and making judgments and decisions about the imagery)
must possess good color skills to fully and accurately exploit the imagery.
The most important skill is color discrimination, i.e., being able to
perceive differences between colors that are very similar. Also, being
able to accurately identify the name or designation of a color, and
communicating that color name will be a critical skill throughout the
operational units of the Center. The capability of average individuals
in these skills is discussed below.
Color discrimination is defined as the ability to report (or
respond to) differences among colors, i.e., differences in hue, saturation,
or lightness. This ability is very important in photointerpretat:Lon of
color imagery and mensuration. Color differences are the primary cues
that may lend an advantage to color imagery, particularly for target and
change detection, and for determining edges.
Since colors can vary in hue, saturation, and lightness, normal
discrimination ability can be expressed in terms of these dimensions as
well as total color-discrimination ability. In the following discussion,
it must be remembered that discrimination ability varies with both the
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type and the level of the illumination, and with the size of the color
field (degrades rapidly below 1/2 to 1 degree). It also varies among
people.
Discrimination of lightness differences at everyday light levels
(1 to 1000 foot lamberts) is approximately constant over the spectrum of
400 to 700 nanometers (Burnham, et al,, 1963). At lower light levels this
is not true, but low light levels should not be used with color imagery.
Just-perceptible-lightness differences are generally less than .05.
Discrimination of saturation differences may be expressed as the
number of discernible steps from neutral gray. Note in Figure 2.12, that
the least number of steps occur around 570 nanometers (yellow-green),
whereas larger numbers of steps are discernible at the extremes of the
spectrum (reds, blues, and some greens).
Discrimination of wavelength differences can be expressed as the
number of nanometers of wavelength that must be added to or subtracted from
a given wavelength to allow the observer to perceive a difference or change.
Figure 2.13 shows that over most of the spectrum 1 to 2 nanometers are
required, but at the extremes of the spectrum 2 to 6 nanometers are
required.
Discrimination among all colors (including hue, lightness, and
saturation) can be expressed in terms of the number of different colors that
can be seen by the normal eye. Theoretical estimates range in the
millions. Practically no existing displays (including color films) record
all these colors. The normal human visual system's capability to
discriminate among color exceeds the capacity of existing displays to
present them.
2.5.2 Color Memory
Although our visual system can discriminate among millions of
colors, our memory of colors is very unreliable. Color memory may be
defined as an observer's judgment as to the color of an object without the
use of a physical reference standard, e.g., Munsell Color Chips.
Until an individual has had some experience with an object or
scene, color memory is unreliable, i.e., color matches or color naming
will be highly variable with or without the object being present. However,
once experience has been gained, the factor which is dominant in the
object's color will tend to be exaggerated in memory recall. For example,
bright objects will tend to be remembered as brighter than they actually
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L.C.M.
. X_ --x
x~ ? ?
The separate
points '0'
represents the
results of Jones
and Lowry
L I 1 1 1
450 500 550 600 650
Wavelength, nanometers
NUMBER OF JUST-PERCEPTIBLE STEPS BETWEEN
NEUTRAL (color temperature 4800 K) AND
THE SPECTRUM COLORS. (Wright, 1947).
i l l r-T-7-FTi -17-71
LZ
L 1 1 1 1 I! I I I ~! 11 1[ I! I
450 500 550 600 650
Wavelength, nanometers
FIGURE 2.13 DIFFERENTIAL COLOR SENSITIVITY. From LeGrand,
(translated by R. W. G. Hunt, J. W. T. Walsh,
and F. R. W. Hunt, New York: John Wiley and
Sons, Inc., 1967).
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were and dark objects as darker. Saturations will be increased, e.g., a
pink will be more red on memory recall. Hue shifts will also emphasize a
predominating color. In most instances, perceptions will be consistent with
what the individual observer has found to be pleasing for a given object,
as well as what the object might normally be expected to look like. Over
time, color-memory reliability decreases, but with training and practice,
reliability can be increased (Hanes and Rhoades, 1959).
2.5.3 Color Naming
Color naming, or identification, is identifying a color without
the availability of a closely matching reference color. This ability is
mostly dependent upon color memory and, as a result, limits the number of
reliable identifiable colors. If a memory scale is learned, as many as
14-15 hues can be named. Otherwise, it might be as few as 10 (Halsey and
Chapanis, 1951; Hanes and Rhoades, 1959). If brightness and saturation are
allowed to vary along with hue, the number of colors named can be
increased. It is possible to train people to reliably name colors (up to
40-50 perhaps), but training time is extensive and periodic practice is
required (Hanes and Rhoades, 1959). Such an ability is rarely needed,
however, since references are available with colors already named, e.g.,
ISCC-NBS color system.
2.5.4 Color Matching (see also 3.4 COLORIMETRY)
The ability to match colors is one of the most demanding of the
color abilities. Essentially, it requires the observer to find a percep-
tually perfect or near-perfect color match from a set of colors, to match
a test color. At the Center, color matches are most likely to be limited
to positive transparencies, glossy prints, and matte proofs (or paper).
Usually, the purpose of matching is to determine if two colors are the
same, or to determine the name or reference number of a color through
colored reference samples.
For optimal and precise color matching, there are several
requirements:
(1) The. illuminant should be the same (both type and
intensity level) for both color samples. The use
of different illuminants or intensity levels causes
colors to be perceived differently and, thus,
cause matching errors.
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(2) The colors being matched should be on the same
(or nearly the same) type of material. The surface
of a color affects the perception of that color.
A matte red surface looks different than a glossy
red surface, and both look different from a red
area on a transparency. Yet all these reds could
be identical.
(3) The size of the observers field-of-view for both
colors should be the same. Two apertures in a
neutral gray field, one for each color, would solve
this requirement.
(4) The viewing angle should be the same for both
colors.
(5) The two colors should be surrounded by a neutral
gray field (see 2.3.2 Simultaneous Contrast and
Edge Effects, and 2.3.3 Spreading Effects).
(6) The observer must, of course, have normal color
vision. However, even within the normal range there
is sufficient variation to cause differences and
disagreements among "normal" individuals. Thus,
perfect color matches are probably impossible,
and it is "estimated that a perfect match by a
perfect 'average' observer would probably be
unsatisfactory for something like 90 percent of
all observers" (Evans, 1948, p 196). Individuals
whose color vision is defective, e.g., dichromats
(red-green or yellow-blue color weak) and
monochromats (almost totally color blind) would
make matches even more unacceptable to normal
observers. However, observers with defective
color vision may be satisfied with matches made
by a normal observer, because they cannot detect
differences. Yet, unless that match is perfect,
it may be made unacceptable to other normal
observers. Thus, two observers may agree on a
match, yet both may have normal color vision, or
one may be color defective. The significance of
this problem is that all individuals involved
should be color-vision tested, and disagreements
among normal observers can be expected.
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How stringent these requirements must be followed, depends on the
precision required in matching colors. In addition, with training and
practice, observers may be able to adapt to variations in these requirements,
e.g., texture differences or differences in intensity levels.
Under conditions of adequate lighting, virtually everyone can
discriminate colors to some degree. Those extremely rare individuals that
cannot do so (although they can still detect light and brightness
differences) are truly color blind. A large group of people (often up to
10 percent of any population sample) are color weak, i.e., they will see
colors, but identify or match some of them differently, depending on their
individual defect. Various possible defects are described in 2.6.1.1.
All people may be classified as either color normals or color
defectives. Very few people, however, have this information about
themselves, and most people believe they have normal color vision. An
adequate description or classification. can be made only on the basis of a
carefully performed, objective test. Theoretically, a test can be made fine
enough to show differences between color normals. However, such differences
would be insignificant in terms of the practicalities of most color-vision
problems, except perhaps obtaining agreements on color matching (see
2.5.4 Color Matching). Therefore, classification is usually limited to
normals and the various types of defectives. Quantification of the defect
is usually a pass-fail type of labelling. Further subdividing can be done,
although in the context of the practical problem, it is troublesome and
expensive, particularly when it is considered that the usual classification
problem is simply separating defective from normals.
Although most people have normal color vision, a significant
minority, ranging from 8 to 10 percent of the population (less than 10%
of these
are
female), have one of several color defective conditions.
Awareness
of
and knowledge of some of the details of the phenomenon are
important
to
anyone involved with color, primarily because of the reliance
placed on
the
detection of small color differences.
Not all color defectives are color blind. Also, there are a
large variety of types and many degrees of severity among color defectives.
Basically, there are two problems with color defectives: (1) a failure to
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detect normal color differences, and (2) confusion in communicating colors
to other people. Obviously, these problems are critical at the Center.
2.6.1.1 Types of Color Vision Defects
A person with normal color vision is called a TRICHROMAT,
because he can match any pure spectral color with'a mixture of three
primary colors (red, blue, and green).* His description can be found in
Sections 2.2 Color Sensitivity of the Visual System, and 2.5 Color
Capabilities and Skills. However, not all trichromats have the same
sensitivity to color, and thus, there is a range of normal color vision.
Outside this normal range, fall the individuals known as color defectives.
The three relevant categories of color defectives are MONOCHROMATS,
ANOMALOUS TRICHROMATS, and DICHROMATS. Monochromats are totally color
blind and see only brightness differences. Usually there is also a
reduction in visual acuity and other eye problems.
Anomalous trichromats resemble the normal trichromats in that
they use the three primary colors (red, blue, and green) to match colors
and they can perceive all colors. However, the amounts of the primary
colors needed to make the match will differ from that of the normal
trichromat. The two most common of the anomalous trichromats are known
as DEUTERANOMALS (4.9 percent of males, 0.39 percent of females) and
PROTANOMALS (1.0 percent of males, 0.02 percent of females). The former
needs more green to make his matches agree with normals. The latter
usually requires more red. Both have difficulty in making distinctions
between reds and greens.
With good lighting and adaptation, anomalous trichromat:s seem to
see the same colors as normal individuals, but they differ in color matches
and, perhaps, color naming. How important this defect is to color-image
interpretation will depend on how critical color identification becomes
to the interpretation task. The performance of any Center interpreters
with this type of defect who will be judging, matching, and naming colors
will be somewhat affected.
Dichromats are people that are partially color blind. The two
principal types are PROTANOPES (1.0 percent of males, 0.02 percent of
females), and DEUTERANOPES (1.1 percent of males, 0.01 percent of females).
* Theoretically any color can be matched by a proportional mixture of
red, green, and blue. All individuals with normal color vision would
mix these in the same approximate way to match a particular color.
Anyone who has marked differences in these proportions is color defective.
For example, if an individual uses more green than usual for a color,
his eyes must be weak in green.
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The former is less sensitive, or "blind" to the extreme red end of the
spectrum and see reds and bluish-greens as gray. The latter have a
similar difficulty (although usually not as severe) with greens, and see
greens and bluish-reds as gray. Their common problem, along with the
anomalous trichromats, is the detection of red-green differences.
The TRITANOPES (0.002 percent of males, 0.001 percent of
females) are individuals that are weak in blues and see purplish-blue and
greenish-yellows as gray. For reasonably large areas of sample colors,
this type of defect is much rarer than either protanopia or deuteranopia.
However, for central (foveal) fixation at extremely small viewing angles
(less than 1/2 degree), it is considered universal and called SMALL-
FIELD TRITANOPIA. Thus, anyone staring at a very small area will
experience a loss of blue. This is not ordinarily noticed, since the
fixation of the eye continually wanders.
The dichromat will often fail to detect a difference between
samples matched by normal trichromats. In fact, he will usually agree with
such matches. Also, he will have difficulty discriminating between
certain colors. Clearly, for the interpretation of color imagery (detection
of color differences) and the judging,, naming, and matching of colors,
dichromats could have difficulties, and may cause errors.
2.6.1.2 Congenital versus Acquired Color-Vision Defects
Most authorities usually think of color defective vision as a
condition that began before birth and will continue throughout one's
life-time, with no hope of a cure. These are congenital color-vision
defects. So-called training programs for correction can do little more
than teach an increased reliance on brightness perception and memorization
of some test patterns used in examination of color vision.
Various acquired forms of color blindness, fortunately, do not
occur too frequently. They are usually symptoms of conditions affecting
the eyes, i.e., the defect in color vision is secondary to some other main
effect elsewhere in the body. In some instances, acquired damage is
permanent, while in others, it can be cured.
2.6.1.3 The Effects of Age on Color Perception
Color perception begins to alter around the age of 25 to
30 years, but the change is very slow and does not become pronounced until
after the age of 60. The actual change is a slight attenuation at the
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lower end of the spectrum (blue region) due to scattering resulting from
an extremely slow progressive sclerosing (hardening) of the lens of the
eye. The amount of this effect and the age of onset are extremely variable.
To the individual, the change is a visual world which is slightly, but
continually becoming progressively more yellow.
Some color-vision tests may have immediate application to the
Center. While these tests seem to be the most appropriate, they are a
substitute for a test or series of tests that should be specially developed
for the Center. The tests discussed may be optimal as a starting program,
but their effectiveness cannot be evaluated until (1) studies on how color
affects the task of Center personnel, and (2) validation studies on work
performance of personnel that have taken the tests, have been completed.
An additional possible shortcoming of the tests is that they all
emphasize reflected light, whereas photointerpreters, photogrammetrists
and others, use transmitted light for viewing color imagery.
2.6.2.1 Pseudoisochromatic Chart Tests (PIC)
These include Stilling, Ishihara, Dvorine, and American Optical's
Hardy-Rand-Rittler, as well as several other less readily available
versions. These are test charts, usually viewed by reflected light
(although some occupational vision desk-top tester devices use
transilluminated targets). The purpose is to screen out and, to a certain
extent, classify color defects. PIC tests are not used for evaluation of
higher color skills such as matching. No one test has been found
consistently best (Lewis and Ashby, 1967), although the Ishihara and
American Optical's Hardy-Rand-Rittler are most popular.
Test plates are constructed of a large variety of sizes of dots.,
or circles, the value, hue, chroma, and areas of which are arranged so that
the viewer or testee will see (from a normal reading distance of 14 in.)
a figure, letter, or shape if he is a normal trichromat. However, the color
defective will see only a confusion of dots. In other plates, the situation
is exactly reversed. A third type of plate is devised so that the color
normal will see one type of figure and the color defective will see
another. A large variety of plates is available so that some classification
of color defectives is possible.
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2.6.2.2 The Farnsworth-Munsell 100-Hue Test (FMT)
This is a color-discrimination test that divides people into
three groups: low, normal, and superior color aptitude, on the basis of
their color-discrimination ability. It will also detect, screen out, and
approximately classify all types of color defectives.
The apparatus comprises four wooden panels or racks and 85 round
plastic caps of color samples (with black borders) equally spaced in
Munsell hue and of about equal value and chroma. The task for the testee
is to arrange all of the discs in sequence according to his perception of
their hue. He is given two minutes to complete each of the four racks,
although no provision is made for analysis of time in scoring. Farnsworth
recommended a minimum of two tests per individual, and usually took the
average of the two as the score (Farnsworth, 1957).
The scoring is a measure of the number and way the discs are
transposed out of the correct sequence:. A unique property of the test is
the method of graphing the score. A specially prepared polar coordinate
plot is available from the test suppliers. The circumference represents
the sequence of hues represented by the 85 color samples. The radius to
any point on the circumference represents the correctness of the response.
The sum of all radii represent the total score, which is inversely related
to color aptitude (the lower score shows high aptitude).
Thus, if all points on the plot are connected, a small tight
circle would be a low score, and the testee, a good color discriminator and
a normal trichromat. A large circle would be the higher score of a poor
color discriminator, but a normal trichromat. Any localized projections
from the circle would increase the score and indicate the colors that the
testee had difficulty with, with respect to both perception and
discrimination.
Thus, the test can also be used to corroborate evidence of color
defects from other tests.
2.6.2.3 The Inter-Society Color Council Color
Aptitude Test (ISCC-CAT)
This is a test of color matching of square chips seen by reflected
light and takes approximately an hour to administer. It was developed to
select people in industry known as "shaders" who are on production or quality
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control jobs, and, thus, are responsible for the color uniformity of a
given product. They are expected, as part of their job qualifications, to
have superior color aptitudes.
The test is made up of two identical sets of 48 chips. One set
is permanently mounted on an easel, inclined at a 45 degree angle, in front
of the person being tested. Of the 48, only 40 are used for scoring. The
mounting arrangement is such that there are four rows, each corresponding
to one of the hues (blue, red, green, and yellow), and chips within these
rows are randomly arranged on the basis of saturation. The graduations
in the steps are about 0.2 Munsell Chroma (saturation) steps.
The second set of 48 chips is identical to the first and
randomized in a preset standardized order. The person being tested pushes
out each new chip when he is ready to make a match placing it on the easel
below the chip which he feels is the closest match. Only one match is
possible at a time since each chip must be returned to the rear of the
dispenser in order to get a new one.
The total test score is the sum of individual match scores, which
in turn is a measure of the closeness of the match. Time is usually not
controlled. However, if it were, standard scores under such time
limitations would have to be developed.
There is no prerequisite for color normality to take this test,
and some color defectives have done well because they have learned to rely
on cues of brightness and color saturation for "color" discrimination.
However, a color defective will usually be revealed by a relative poorer
score on one of the rows of a single hue.
2.6.2.4 The Burnham-Clark-Munsell
Color-Memory Test (BCMS)
This is a test of short-term color memory. Although not
commercially available, Burnham (Garra and Briggs, 1970) has indicated that
the experimental materials could be made available. On the basis of the
analysis by Burnham, Hanes, and Bartelson (1963) it appears to be better
than the only other color-memory test available, the Woods Color Aptitude
test.
Procedurally, the testee looks for five seconds at one of 20
variously colored test chips mounted in a wheel and then covers it for
five seconds. At this point, with only the memory of the test chap as a
reference, he selects the best possible match from one of 43 comparison
chips.
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2.6.2.5 Campimeter Test
All of the foregoing tests are measures of the color aptitude of
central vision. Peripheral vision is also used, particularly during
screening and scanning of imagery. Therefore, it is suggested that the
color detection and discrimination properties of a photointerpreter's
peripheral vision be tested. A plot of the geometric color zones of the
eye (see Section 2.2.3) can be made using either a campimeter or a
perimeter. The campimeter is preferable since it emphasizes the central
portion of the retina where the sensitivity to color is maximum.
However, no standards are available to classify people into
categories of good to poor peripheral color vision.
2.6.2.6 Explanation of Test Battery Usage
The foregoing represents a tentative battery of available tests.
The first two tests would be used for initial classification. The PIC
would select color defectives out of the total population and the FMT would
classify the color discrimination ability of the color normals into three
groups (low, normal, and superior) and substantiate PIC findings on color
normality.
Finer measures of color discrimination would be obtained by the
ISCC-CAT that is designed to measure small differences in superior color
discriminators, and that could be used to measure changes in color ability
as a result of training and/or color experience.
Furthermore, measures of color memory and peripheral color
sensitivity could also be taken. These specifically could be done with the
BCM color-memory test and the campimeter, although both should have further
development work.
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Bartleson, C. J., "Memory Color of Familiar Objects", Journal of
the Optical Society of America, 50(1), pp. 73-77 (1960).
Boynton, R. M., Schaefer, W., and Neun, M. E., "Hue Wavelength
Relation Measured by Color-Naming Method for Three Retinal
Locations", Science, 146, pp. 666-668 (1964)'.
Brown, W.R.J., "The Influence of Luminance Level on Visual
Sensitivity to Color Differences", Journal of the Optical
Society of America, 41(10), pp. 684-688 (1951).
Brown, W.R.J., "The Effect of Field Size and Chromatic Surroundings
on Color Discrimination", Journal of the Optical Society of
America, 42(11), pp. 837-844 (1952).
Burnham, R. W., Hanes, R. M., and Bartleson, C. J., Color: A
Guide to Basic Facts and Concepts, John Wiley and Sons, New York
(1963).
Cavonius, C. R., "Human Visual Acuity Measured With Colored
Stimuli", Final Report, AR-65/8-Cr, Human Sciences Research
Incorporated, McLean, Virginia (1965).
Cavonius, C. R., "The Effect of Wavelength on Visual Acuity"',
ERF-RR-1/67/Cr, Eye Research Foundation, Bethesda, Maryland
(1967), AD 646575.
Chapanis, A., and Halsey, R. M., "Absolute Judgements of Spectrum
Colors", The Journal of Psychology, 42, pp..99-103 (1956).
Charman, W. N., and Watrasiewicz, B. M., "Mach Effect Associated
With Microscope Images", Journal of the Optical Society of
America, 54(6), pp. 791-795 (1964).
Committee on Colorimetry - Optical Society of America, The
Science of Color, Thomas Y. Crowell Company, New York (1953).
DeValois, R. L., and Jacobs, G. H., "Primate Color Vision",
Science, 62, pp. 533-540 (1968).
Dwyer, W. 0., and Lit, A., "Effect of Luminance-Matched Wavelength
on Depth Discrimination of Scotopic and Photopic Levels of Target
Illumination", Journal of the Optical Society of America, 60_(1),
pp. 127 (1970).
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Diamond, A. L., "Simultaneous Brightness Contrast and the
Pulfrich Phenomenon", Journal of the Optical Society of America,
48(12), pp. 887-890 (1968).
Dimmick, F. L., "Methodology in Test Preparation", Journal of
the Optical Society of America, 3(6), pp. 308-315 (1943).
Emsley, H. H., Visual Optics, Hatton Press Limited, London,
England (1950).
Evans, R. M., An Introduction to Color, John Wiley and Sons,
New York, New York (1948).
Farnsworth, D., The Farnsworth-Munsell 100-Hue Test for the
Examination of Color Discrimination Manual, Munsell Color Company,
Baltimore, Maryland, Rev. Ed. (1957).
Fry, G. A., Bridgeman, C. S., Ellerbrock, V. J., and Allen, M. J.,
"Means for Measuring and Compensating Chromastereopsis With
Special Reference to the Use of the M-1 Height Finder", Report to
the National Defense Research Committee (1943).
Garra, A. A., and Briggs, S. J., "Image Interpretation - State
of the Art Review", The Boeing Company, Aerospace Group, Seattle,
Washington (1970).
Graham, C. H., Vision and Visual Perception, John Wiley and Sons,
New York, New York (1965).
Halsey, R. M., "Identification of Signal Lights. I. Blue,
Green, White, and Purple", Journal of the Optical Society of
America, 49(1), pp. 45-56 (1959).
Halsey, R. M., and Chapanis, A., "On the Number of Absolutely
Identifiable Spectral Hues", Journal of the Optical Society of
America, 41(12), pp. 1057-1058 (1951).
Hanes, R. M., and Rhoades, M. V., "Color Identification as a
Function of Extended Practice", Journal of the Optical Society
of America, 49(11), pp. 1060-1064 (1959).
Hilz, R., and Cavonius, C. R., "Wavelength Discrimination
Measured With Square Wave Gratings", Journal of the Optical
Society of America, 60(2), pp. 273-277 (1970).
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Hoffman, C. S., "Comparison of Monocular and Binocular Color
Matching", Journal of the Optical Society of America, 52(1),
pp. 75-80 (1962).
Jameson, D., and Hurvick, L. M., "Perceived Color and Its
Dependance on Focal, Surrounding, and Preceding Stimulus
Variables", Journal of the Optical Society of America, 49(9),
pp. 980-998 (1959).
Judd, D. B., "Color Blindness and the Detection of Camouflage",
Science 97, pp. 544-546 (1943).
Judd, D. B., "Facts of Color Blindness", Journal of the Optical
Society of America, 33(6), pp. 294-307 (1943).
Judd, D. B., and Wyszecki, G., Color in Business, Science and
Industry, Second Edition, John Wiley and Sons, New York (1963).
Kishto, B. N., "The Color Stereoscopic Effect", Vision Research,
5, pp. 313-329 (1965).
Lakowski, R., "Psychological Variables in Colour Vision Testing",
Paper #52, read at the First Institute Congress on Colour,
9-13 June 1969, Stockholm, Sweden, AD 695343.
LeGrande, Y., Light, Color and Vision, 2nd Edition, Chapman and
Hall Ltd., London, England (1968).
Lewis, M. F., and Ashby, F. K., "Diagnostic Tests of Color
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Lit, A., Dwyer, W. 0., and Morandi, A. J., "Effect of Background
Wavelength on Stereoscopic Acuity at Scotopic and Photopic
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45(3), pp.195-203 (1968).
MacAdam, D. L., "Small-Field Chromaticity Discrimination",
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pp. 1143-1146 (1959).
MacAdam, D. L., "Visual Sensitivities to Color Differences in
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Mockovack, W. P., and Chason, L. R., "The Effects of Sound on
Color Intensity Perception", A paper delivered at the 14th Annual
Human Factors Convention (1970).
Murray, Elsie, "Evaluation of Color Vision Tests", Journal of
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Newhall, S. M., Burnham, R. W., and Clark, J. R., "Comparison of
Successive With Simultaneous Color Matching", Journal of the
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Ruddock, K. H., "The Effect of Age Upon Color Vision - I Response
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the Optical Society of America, .50(8), pp. 785-790 (1960).
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Perception and Psychophysics, 8(.5b), pp. 343-347 (1970).
Von Helmholtz, H., Physiological Optics, trans. & ed. by
J.P.C. Southall, Dover, New York (1962).
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Wolff, E., The Anatomy of the Eye and Orbit, Third Edition,
Blakiston, Philadelphia, Pennsylvania (1948).
Wright, W. D., Researches on Normal and Defective Colour Vision,
C. V. Mosby, St. Louis, Missouri (1947).
Wyszecki, G. and Stiles W. S., Color Science: Concepts and
Methods, Quantitative Data and Formulas, John Wiley and Sons,
New York (1967).
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Inc., Chicago, Illinois (1947).
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"For the Rays (of light) to speak properly are
not coloured. In them there is nothing else
than a certain Power and Disposition to stir
up a sensation of this or that colour."*
Newton recognized that color is a complex phenomenon with many
different physical and psychological aspects. Figure 3.1 is one way of
illustrating this psychophysical nature of color. The observer represents
the psychological aspects of color. The light source and object represent
those aspects of color that are characterized by mass, length, and time --
the dimensions of the physical world. Understanding this dual psycho-
physical nature of color is important to the reader, because these
elementary concepts are the foundations for the following discussion of
color, color perception, and color measurement**.
A light source converts various forms of energy, e.g., chemical,
electrical, mechanical, into LIGHT, a form of energy to which the eye is
visually sensitive. The propagation of light, i.e., energy, away from a
source is quite analogous to the outward movement of small periodic waves
from the point at which a pebble, i.e., energy source, strikes the surface
of a pool of still water. The passage of light or transport of energy
through space is described by what are called ELECTROMAGNETIC WAVES. The
WAVELENGTH denotes the distance after which the electromagnetic wave
repeats, i.e., the distance between corresponding points on adjacent waves.
The eye is sensitive to only those wavelengths from slightly less than
400 nanometers to slightly greater than 700 nanometers (nanometer = 10-9
meters). Thus, light is a very small part of the electromagnetic spectrum
illustrated in Figure 3.2.
Light sources are characterized in terms of the relative
energy emitted at each wavelength. A graph showing the energy emitted by
a source as a function of wavelength is a SPECTRAL ENERGY DISTRIBUTION
CURVE. The curve for a typical 40-watt incandescent lamp is shown in
Figure 3.3, and that for a typical 40-watt fluorescent lamp in Figure 3.4.
* Newton, OPTICKS - from Billmeyer and Saltzman (1966)
** A more detailed treatment of these topics can be found in the
following texts: Evans, 1948; Wyszecki and Stiles, 1967; Billmeyer
and Saltzman, 1966; Burnham, Hanes, and Bartleson, 1963; Judd and
Wyszecki, 1963; Hunt, 1967.
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FIGURE 3.1 THE ESSENTIAL ELEMENTS OF COLOR (Billmeyer and Saltzman, 1966)
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N
c 4
a)
0
a)
ry
N
10oI- I 1 1
300 400 500 600 700
Wavelength, nano meters
FIGURE 3.3 THE SPECTRAL ENERGY DISTRIBUTION
FOR A 40-WATT INCANDESCENT LAMP
0 I I I I
300 400 500 600 700
Wavelength, nanometers
FIGURE 3.4 THE SPECTRAL ENERGY DISTRIBUTION
FOR A 40-WATT DAYLIGHT FLUORES-
CENT LAMP
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Four things happen to the light that reaches an object. A frac-
tion of the incident light is ABSORBED and dissipated within the object.
Another fraction of the incident light is SCATTERED and does not reach
the eye of the observer. The incident light that is neither absorbed nor
scattered by the object is in part REFLECTED from the object and in part
TRANSMITTED by it. The ratio of reflected to transmitted light depends
on the nature of the object. A piece of white paper reflects most of the
incident light, whereas a piece of clear glass transmits most of the
incident light.
Objects in general do not reflect or transmit all. wavelengths
of incident light equally. At a given wavelength the ratio of light
incident to light reflected or transmitted by the object is, called
respectively, the SPECTRAL REFLECTANCE or SPECTRAL TRANSMITTANCE of the
object. A graph in which the spectral reflectance (transmittance) is
plotted for each wavelength throughout the spectrum is a SPECTRAL
REFLECTANCE (TRANSMITTANCE) CURVE for that object.
Because light sources emit different amounts of light at each
wavelength and objects reflect or transmit different amounts of light at
each wavelength, the spectral composition of the light reaching the
observer is a combination of the spectral energy distribution of the
source and the spectral reflectance (transmittance) of the object. On
the basis of logic and experimental evidence, the spectral composition
of the light reaching the observer is known to be the same as the product
formed by multiplying, wavelength by wavelength, the spectral distribution
curve of the light source by the spectral reflectance (transmittance)
curve for the object. An example of this point-by-point multiplication
and the spectral energy distribution of the light reaching the observer
are shown in Figure 3.5.
As discussed in Section 2.0, the observer's eye is not equally
sensitive to all wavelengths of light. For normal room-lighting and
image-viewing conditions, the standardized visual sensitivity or spectral
response of the eye is given as the photopic curve (shown in Figure 2.6
and the middle of Figure 3.6). As is shown in Figure 3.6, the COLOR
STIMULUS the observer receives is the combined product of the spectral
energy distribution of the light and the spectral response characteristics
of the eye. The eye transforms this color stimulus into nerve impulses
that are sent to the brain. The observer perceives a color or experiences
the sensation of color when this message is processed by the brain.
The physical aspects of color are concerned primarily with
controlling and measuring the color stimulus that the observer receives
and not with the nature of the color sensations that this color stimulus
produces in the observer's brain. Although there are several exceptions,
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2.0 (-curve for a light source
01 1 1 1
400 500 600 700
Wavelength, nonometers
Spectral reflectance curve
- for the object being observed
01 1 1 1
400 500 600 700
Wavelength, nanometers
Spectral-energy distribution curve
for the light reaching the observer's
eye
I I I
400 500 600 700
Wavelenath,nanometers
FIGURE 3.5 THE SPECTRAL ENERGY DISTRIBUTION OF THE LIGHT
REACHING THE OBSERVER'S EYE
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Spectral energy distribution- > Standardized visual sensitivity or spectral
curve for the light reaching response curve for the observer's
0
1
.
F eye
the observer's eye
09 1 1 1
400 500 600 700
Wavelength, nanometers
Wavelength nanometers
Color stimulus experienced
by the observer
400 500 600 700
Wavelength, nanometers
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the spectral energy distribution of the color stimulus the observer
receives is only roughly correlated with the color sensation this stimulus
produces. The nature of the color sensations a color stimulus creates in
the observer's brain are described best by the psychological aspects of
color perception.
The three psychological aspects of color perception are HUE,
SATURATION, and LIGHTNESS. Hue is denoted by red, blue, green, yellow,
etc.; saturation is associated with the strength of a hue; lightness is
that aspect by which an observer distinguishes between two achromatic
(gray) objects* As the color stimulus is changed, the observer will
perceive colors with different hues, saturations, and light.nesses..
Two basic techniques are used to reproduce color. Although they
appear to be quite different, in principle, they are the same. An
understanding of color reproduction will help the Center's personnel to
develop an appreciation for the limitations and potentials of high-
resolution, high-quality color photography and reproduction.
In the ADDITIVE process, a given color is reproduced by adding
or blending varying amounts of any three conveniently selected colored
lights, such as red, blue, and green. For example, cyan, a blue-green
color is created by projecting both blue and green light onto a common
area of a white screen. Similarly, yellow is produced by projecting red
and green light, and magenta is produced by projecting red and blue light
onto a common area of a screen. The visual sensation of white is created
by projecting the proper proportions of the three selected colors, i.e.,
red, blue, and green, onto a common area of a white screen. Obviously,
black or no color would be perceived if there is very little or no
light projected.
In the SUBTRACTIVE process, a color is reproduced by using
colored filters* to selectively remove practically all the undesired
colors from a beam of white light. For example, red reults from
optically removing all colors except red from a beam of white light by
using a red filter. Actually, since filters are not perfect, not quite
all the undesirable color can be removed.
* A colored filter is an optical device that transmits particular
wavelengths of light. For example, a green filter transmits primarily
green light, and therefore, appears green to the normal observer.
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3.2.1 The Additive Method of Color Reproduction
In principle, the additive color process reproduces a given
color by adding or blending varying amounts of any three colors, e.g.,
red, blue, and green.. This principle of additive color reproduction
can be applied to color photography in the following way. Three simulta-
neous exposures of a scene are made with three equivalent cameras, located
in approximately the same position. PANCHROMATIC black and white film in
the cameras is exposed through red, blue, and green filters, one filter
for each camera. Thus, the positive transparencies made from the three
original negatives contain the red, blue, and green records of that scene.
To reproduce this scene, the transparencies are projected through the
appropriate filter, in register, onto a white screen. For example, only
red light is emitted from the projector containing the red transparency
record of the original scene. When the relative intensities of the
three projectors are properly adjusted, the composite image on the screen
approximates the color of the original scene. This general concept of
additive color reproduction is illustrated in Figures 3.7 and 3.8. There
are several modifications of this additive process, and some of them are
capable of excellent color reproduction. However, the Center has not
found it useful for intelligence extraction, because perfect registry
is extremely difficult.
3.2.2 The Subtractive Method of Color Reproduction
Although color photographic films vary from one manufacturer to
another, all subtractive color processes use some combination of CYAN,
YELLOW, and MAGENTA dyes in layers of the film to act as filters.
Spectral transmittance curves for a set of ideal cyan, magenta, and yellow
dyes are shown at the top of Figure 3.9. Although an ideal cyan dye
transmits light only in the blue and green portions of the visible
spectrum, an actual dye will transmit some light in the red portion of the
spectrum. As shown in the diagram, the magenta dye transmits a combination
of red and blue light; the yellow dye, a combination of red and green
light. Actual magenta and yellow dyes also transmit some extraneous
wavelengths. The transmission of colors other than those for which the
dye layers were designed is one of the major problems in reproducing
imagery with the desired color balance and fidelity. As an example, if
the "blues" are faithfully reproduced, then more than likely the "reds"
and the "greens" in the image will not be a faithful reproduction of the
original colors in the scene.
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FIGURE 3.7 ADDITIVE COLOR PHOTOGRAPHY- TAKING THE PICTURE
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LUE-GREEN
(CYAN)
-,-
--'RED, BLUE
AND GREEN
(WHITE)
FIGURE 3.8 ADDITIVE COLOR PHOTOGRAPHY - RECONSTRUCTING THE PICTURE
ems
rs s~{ 5{
t \e
Q t o\ec
Ut erC`e5
{c arse
?os\{
\o 9s
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Cya n
Magenta
50 50 50
N
z
Q 400 500 6 0 700 400 500 600 700 400
V
U, o
U Cyan combined with magenta Yellow combined with cyan
z transmits blue light transmits green light
~- 100 100
a 50 - 50
Q!
J
Q
~ 0
V
WAVELENGTH (nanometers)
Blue
Yellow
Magenta combined with
yellow transmits red light
FIGURE 3.9 SPECTRAL TRANSMITTANCE CURVES FOR IDEALIZED CYAN, MAGENTA, and YELLOW DYES
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The center of Figure 3.9 indicates how various colors can be
reproduced or matched by using various combinations of dyes. For example,
blue will be seen when a white light is viewed through a filter containing
a dispersion of both a cyan and magenta dye. The cyan filter transmits
blue and green, and the magenta transmits blue and red. The color not
blocked out by either filter is blue. The same blue color is seen when
a white light is viewed through a filter formed by combining separate cyan
and magenta filters.
The principle of subtractive color reproduction is used in most
color positive films. The configuration of a typical color-positive or
color-reversal" film is illustrated at the top of Figure 3.10. The film
comprises at least four separate layers of photographic materials. The
yellow layer (i.e., a minus blue filter) located below the blue-sensitive
top prevents the blue light that exposes the top layer from also exposing
the two bottom layers. These two bottom layers of photographic material
in a typical color positive film are sensitive to green and red light,
respectively. Although the drawing in Figure 3.10 shows these layers as
being sensitive to only one particular color of light, they do have some
sensitivity at all wavelengths. When a conventional color-positive film
is exposed to a multicolored target like the one at the top of Figure 3.10,
the response of each of the separate Layers represents the red, blue, and
green records of that particular scene. The exposed film is processed in
a series of chemical baths. During the processing, the silver particles
of the images, which are the records of the reds, blues, and greens in
original scene, are replaced with images of cyan, yellow, and magenta dyes,
respectively and the color of the original scene is reproduced by the
combined effects of the dye deposits. For example, the image of a red
stop sign is composed of both yellow and magenta dye images (see
Figure 3.9), located in different layers of film. For whites, no dyes are
deposited and for blacks, all three dyes are deposited so that every color
is absorbed. Although the processing chemistry and construction of
positive color materials is simplified here, most systems work by this
same basic principle.
The order of dye layers in S0-242 is inverted from that described above.
In S0-242, the top layer contains 1--he magenta dye deposits, the middle
layer contains the cyan dye deposits, and the bottom layer contains the
yellow dye deposits. The dye layer arrangement in S0-242 is an optimal
arrangement because the magenta image creates the greatest visual effect
on the viewer (see 4.4.1) and film resolution is, to the first approxima-
tion, a linearly decreasing function with increasing emulsion thickness.
Thus, by using the S0-242 type dye layer arrangement, i.e., magneta,
cyan, and yellow, and highly selective spectral sensitizers, it is
possible to produce a high-resolution color film. Also, see Section 4.1
for a detailed discussion of color films.
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White
Black
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Exposure
Silver development
layer
Dye development and bleach
Spectral
sensitivity
Blue
Green
Red
Dye color
White
Block
FIGURE 3.10 A COLOR REVERSAL PHOTOGRAPHIC PROCESS
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Magenta
Cyan
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Although methods for identifying, specifying, and describing
colors have been of scientific and artistic interest for many years, only
in the past fifty years has there been much progress in meeting these
objectives. Much of the impetus behind the development of these color
systems came from an ever-increasing consumer demand for more colors and
better color control. For example, it is important to the automobile
industry that the color of various body parts match, even if they were
made in different locations. Some color systems developed to satisfy
these demands are quite specialized and others are general and can be
applied to a wide variety of color matching, controlling, and specifying
problems. Knowing the various applications and limitations of color
systems is important to the photoint:erpreter and other Center personnel,
because it provides them with a basic understanding of the common terms
used by most people working on the technical aspects of color photography.
The Munsell color system is an orderly arrangement of colored
plaques or chips for use in color matching and identification. The
colors are selected so that there are nearly equal perceptual intervals
between adjacent chips. To correspond to the three-dimensional concept
of color, the Munsell chips are often arranged in the cylindrical pattern
shown in Figure 3.11. In this color-order system, HUE is used to denote
that attribute of color described by words like red, blue, and green, and
is specified in the Munsell system by the capital letters R, B, and G,
respectively. Each major color sector in the Munsell system is subdivided
into smaller parts which are labeled with a numerical designation. For
example, 6Y would be used to label the sixth division of the yellow sector
of the Munsell space. The lightness or darkness of different colors in
this system are designated by the term VALUE. A Munsell value of 0 on
the vertical axis in Figure 3.11 represents black whereas a Munsell
value of 10 at the top of the same axis represents white. Various
shades of gray, the lightness or darkness of a neutral color, are
designated by the Munsell values between these two extremes. For
example, a Munsell value of 7 is used to specify a light gray color.
The term CHROMA in the Munsell color system is used to specify the
saturation or purity of the color, that is, how much that particular
color differs from a neutral gray of the same lightness. For example,
the chroma range of a color, with a hue of 2 YR and value 6, varies from
a light brownish gray (a chroma of 1) to a vivid orange (a chroma of 14).
The Munsell designation of the color of an opaque object is determined by
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S r ~
Light Blue
9B 6/8
Hue Value/Chrome
T 10 (White)
2`4 6 8 10
Chrome
B = Blue
Y = Yellow
R = Red
G = Green
yG = Yellow-green
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visually selecting that Munsell chip which is the nearest visual match
to the color of the object. For example, the Munsell chip that appears
to be the nearest color match to the color of a light-blue car might
have the designation of 9B 6/8, i.e., HUE VALUE/CHROMA.
The CIE (Commission Internationale de 1'Eclairage) color system
is based on the physical aspects of light and color perception; it is
used primarily in the scientific and technical community. Early color
scientists recognized that most colors projected onto a white screen
could be visually matched by projecting varying amounts of red, blue, and
green light from three other projectors onto a common area of the same
screen. As experimentation progressed, it was discovered that individual
observers with normal color vision required approximately the same amounts
of the lights to achieve a match. To standardize color-matching and
-designating procedures and to help communication about color, scientists,
on behalf of the CIE, examined existing color-matching data. These color-
matching data were statistically adjusted and then used to define a new
set of color-matching functions for a STANDARD OBSERVER. These COLOR-
MATCHING FUNCTIONS (x, y, z) are shown in Figure 3.12
In addition to specifying the color-matching functions for the
standard observer, the scientists also specified a set of standard light
sources** known as CIE standard sources A, B, and C. Their spectral
energy distributions are listed in most texts on color science. These
standard distributions are important because the apparent color of a
sample changes as the spectral energy distribution of the light illumina-
ting the sample changes. The other factor that determines the color of
an object is its spectral transmittance or reflectance (see 3.1 THE
PHYSICAL ASPECTS OF COLOR). The CIE designation for a color can be
calculated by combining the color-matching properties of the standard
* Although not specified in the definition of the standard observer,
these color-matching functions are based on color-matching data that
were collected for observers having a 2 degree field of view.
** In this report the terms SOURCE and ILLUMINANT are used as follows:
A SOURCE is a physically realizable light, whose spectral energy
distribution can be experimentally determined. When the determina-
tion is made and specified, the source becomes a standard source
An ILLUMINANT is a light defined by a spectral energy distribution,
which may or may not be physically realizable as a source. If it
is made available in physical form, it becomes a standard source.
(Billmeyer and Saltzman; 1966).
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700 400
Xf-
Z=J ETz dX/f Eyda Y = f TI7 dX/f Fyda X= f ETx dX/( :yds.
X
X= X+Y -Z
T-spectral transmission of sample
E-spectral distribution of light
source
x, V. z-CIE color matching
functions
X,Y.Z-CIE tristimulus values
x y z-CIE chromaticity coordinates
Excitation purity = a
a+b
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observer, the spectral distribution of the standard source, and either the
spectral transmittance or reflectance of the object.
In determining the CIE designation of an object, the first
calculation is to form the product of T, the spectral transmittance (or R,
the spectral reflectance) of the object and E, the spectral energy dis-
tribution of the standard source being used. This operation is demonstrated
for a transparent object at the top of Figure 3.12. A new product is then
formed by multiplying the initial result TE (or RE) times x, y, and z,
the color-matching functions. The curves representing these three products
(TEx, TEy, TEz) are shown at the end of the dashed line in Figure 3.12.
The area under the curves, being the quantity of interest, it is calculated
by standard numerical integration techniques. The CIE TRISTIMULUS VALUES
(X, Y, Z) are the ratios of the areas under each the curves to the area
under the spectral-distribution curve found by the product of spectral
energy distribution of the CIE standard source being used and the y color-
matching function. These tristimulus values are used in the equations of
Figure 3.12 to calculate the CIE CHROMATICITY COORDINATES, x, y, and z.
The CIE color system is designed so that the sum of the values for x, y,
and z is always equal to 1; therefore, it is only necessary to plot two
of the chromaticity coordinates--by convention, x and y--on the CIE diagram
(bottom right of Figure 3.12). The third dimension of the CIE color space,
represented by the tristimulus value Y, is called the LIGHTNESS value of
the color. The CIE tristimulus value Y corresponds to the lightness of the
perceived color, because y is the visual sensitivity or photoptic curve for
the average observer.
Two other terms are used in the CIE system. The DOMINANT WAVE-
LENGTH of a color is represented by that point at which the locus of
spectrum colors or the outer boundary of the CIE diagram is intersected
by the line connecting the points on the CIE diagram representing the color
of the object and the color of the CIE illuminant being used. The CIE
EXCITATION PURITY of a color is a measure of how far the point representing
a color is from the point representing the color of the CIE source and the
locus of spectrum colors. The CIE color system is based on the char-
acteristics of the standard observer, a given light source, and the
reflectance or transmittance of objects being measured. Nevertheless,
some numerical CIE designations can be related to the visually perceived
aspects of color (hue, saturation, and lightness) through terms such as
dominant wavelength, excitation purity, and lightness.
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3.3.3 Lovibond System
The Lovibond color system is a color-specification system based
on a set of glass filters. The various Lovibond glasses are made with a
thin layer of color ' glass flashed onto a clear glass substrate. The
red (R), blue (B), and yellow (Y) glasses* are made by adding gold, cobalt,
and chromium, respectively, during manufacturing. Although calibrated in
arbitrary units, there is a definite relationship between Lovibond glasses
of the same or different colors. For example, a 6Y designation indicates
a glass that has the same spectral transmittance as six 1Y glasses arranged
in series. (This might designate a yellow-appearing filter with a chromium-
enriched glass flashed on the clear supporting layer.) Similarly, a
Lovibond glass designated 1R + 7B would have the same spectral trans-
mittance as a series comprising one 1R and seven 1B glasses. The spectral
transmittance of each Lovibond glass is adjusted so a combination of
glasses with equal red, blue, and yellow designations would approximate a
NEUTRAL DENSITY FILTER.
Typically, Lovibond glasses are used in determining the color of
transparent objects. A LOVIBOND COLORIMETER is usually configured so
that one-half of a back-lighted field of view is filled with the s-^:ple,
and the other with Lovibond glasses. The observer tries various combina-
tions of glasses until he determines a combination that provides the
closest visual match to the sample's color. For example, 20B + .30Y might
be the Lovibond designation for the color of a field of grass recorded in
an aerial photograph.
3.3.4 Ostwald System
Ostwald's color system, which is very useful to artists r.:.d
decorators, is based on the philosophical concept that colors could be
characterized by their FULL-COLOR CONTENT (C), BLACK CONTENT (B), and WHITE
CONTENT (W). His application of these concepts is shown in Figure 3.13.
The spectral reflectance curve in Figure 3.13 is for an idealized colorant
because such step-like changes in spectral reflectance can not be realized
by an actual dye or pigment. The C, B, and W contents of such idealized
colors were defined so that their sum would equal unity, i:e.,
B + W + C = 1 . For a color defined in this manner, the standard Ostwald
notation is a number that specifies one of the twenty-four hues used and
* The spectral transmittance curves for the red, blue, and yellow glasses
indicate they are really magenta, cyan, and yellow glasses. Neverthe-
less, the conventional red, blue, and yellow notations are used.
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White
Content
The color series with
the same white content.
black
FIGURE 3.13 THE OSTWALD COLOR SYSTEM.
66
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two lower-case letters whose combination denotes the white and black
contents of the color, respectively. Although the lower-case letters in
Figure 3.13 are standard Ostwald notation, the numerical values for the
white, black, and full-color content of the various colors have been
included. For example, the Ostwald notation "ne" denotes an Ostwald hue
that has a white content of 5.6 percent, and the black content of 44.0
percent.
The idealized colors in Ostwald system have some very interesting
colorimetric properties. For example, the series of colors in any one of
the diagonal columns have the same dominant wavelength, but their excitation
purity increases toward the outer boundary of the diagram. Those colors in
any vertical column have the same chromaticity coordinates, or constant
excitation purities, but their lightnesses increases from the bottom to the
top of the diagram. The Ostwald hues, arranged in a circular pattern as
shown in the diagram at the lower right of Figure 3.12, represent:
approximately equal intervals of visual perception. Thus, the Ostwald
color system is a possible basis for a psychophysical color system like
the CIE.
The Ostwald color of an opaque object is determined by visually
selecting that Ostwald color sample or chip that is the closest color
match to the color of the object.
3.3.5 DIN System
The DIN (Deutsche Industrie Norm) color system is the official
German color system. The three DIN color coordinates are called
FARBTON (T)*, SATTIGUNG (S), and DUNKELSTUFE (D). In the DIN system, D
is defined as a logarithmic function of the relative lightness* expressed
as the ratio of the luminous reflectance of the color sample to the
luminous reflectance of an optimal color. An optimal color has the
maximum luminous reflectance of all those colors that have the same
chromaticity coordinates as the sample. The D scale in the DIN color
system is equally spaced for both chromatic and achromatic colors. The
dominant wavelengths of the twenty-four different "T's" used in the
system were selected so that different hues would be spaced in nearly
equal perceptual steps. The lines radiating from the point representing
the CIE standard source C in Figure 3.14 are lines of constant DIN-
Farbton or constant T. The curves enclosing the point representing the
* F has also been used.
** A more literal translation of Dunkelstufe would be "darkness degree".
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Line of constant DIN -- Farbton, T= 22
Line of constant DIN - Sattigung, S = 12
Lines of constant T and S are
valid for all values of
DIN- Dunkelstufe, D
FIGURE 3.14 THE LINES OF CONSTANT DIN-FARBTON AND DIN-SATTIGUNG
PLOTTED ON A 1931 CIE DIAGRAM
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C source on the CIE diagram in Figure 3.14 represent levels of equal visual
saturation or constant S.
The color designation of an opaque object is determined by
visually selecting the DIN chip that most nearly matches the color of the
object. This color designation is written as T:S:D. For example, a
yellow rose might be designated as 2:6:1 in the DIN color system.
3.3.6 Densitometric Munsell System
The densitometric Munsell color-measurement system, based on the
Munsell color-order system, is designed for use in extracting colorimetric
information from prints and transparencies. However, the Munsell hue,
value, and chroma of the color of an image is determined by measuring with
densitometers and doing calculating (using nomographs) rather than
visually matching the colors of a target and a Munsell chip. The nomo-
graphs were constructed by measuring the red, blue, green, and visual
reflection densities of a set of selected Munsell chips. Although the
Munsell chips are opaque, the Munsell designation for the color of a
target on a transparency may be determined by using the same nomograph
provided that the transmission densitometer has the same optical char-
acteristics, e.g., acceptance angle, transmittance of filters, etc., as
the reflection densitometer used in constructing the nomographs.
To determine the Munsell color designation of a target in an
aerial photograph, the red, blue, green, and visual reflection or
transmission densities of that target are measured. The differences
between the highest and lowest density reading and between the intermediate
density reading and the lowest density reading are calculated. The ratio
of these differences is also calculated. The Munsell hue, value, and chroma
of the image are determined by using the calculated values and the nomo-
graphs described above.
3.3.7 ISCC-NBS System
The ISCC-NBS (Inter-Society Color Council - National Bureau of
Standards) color system was designed to aid in determining and specifying
the colors of drugs and chemicals; however, it has found a much wider
application in industry and science. The ISCC-NBS color system is
essentially the result of applying a color-naming system to the Munsell
color system. As previously discussed, hue, value, and chroma are the
three dimensions of the Munsell color space, and they are arranged so that
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they form a cylindrically shaped color solid in which all colors having
similar hue, value, and chroma are contained in a small cell or volume of
the solid. The concept of the ISCC-NBS color system is that all colors
whose Munsell coordinates fall within this cell are labeled with and
called by the same name. To conform with the existing color-naming
conventions, the Munsell color volume was arbitrarily divided into 267
individual color cells or color volumes. The hue circle of the Munsell
system was divided into 28 parts and given the names listed in Figure 3.15.
The modifiers to be used with these hue names were selected to denote the
relative chroma and value of the colors contained with a given color cell.
Examples of these hue modifiers are shown in Figure 3.16 for a purple hue.
3.3.8 NuHue, Plochere, Ridgway, Maerz and Paul, Villalobos,
Textile Color Card Association, and Methuin.
Each of these color-naming systems, based on an orderly arrange-
ment of colored plaques or chips, was designed for use by a specific
industry or profession, e.g., the Ridgway system is used by biologists for
labeling specimens and the NuHue system is used by the paint industry to
specify the color of various paints. These systems are adequate for the
specialized purposes for which they were designed; however, it is difficult
to tell anything about a color from the name given to it by these various
color systems. A color designated as Light Blue by the ISCC-NBS color-
naming convention is called Diana, Good Omen, King's Blue, and Forget-me-
not by Maerz and Paul, Polchere, Ridgway, and the Textile Color Card
Association, respectively. Unfortunately, the color chips or samples for
many of these systems were made by using paints whose composition was
unknown or cannot be duplicated.
Colorimetry is the art of measuring the color of an object in
terms of words or numbers that uniquely specify the color of the object
with respect to some specified color system. The purpose of such measure-
ments may be the grading of agricultural commodities such as linseed oil,
or determining the acidity of a solution of known chemical composition.
In all instances, the objective of these measurements is to determine and
specify the color of the object in terms that can be related to some
known and standardized color system. Either visual or instrumental
methods may be used for such measurements of color. Such methods should
be of interest to the Center because a color vocabulary may involve some
aspect of color measurement. Therefore, it is important to have an
understanding of the basic concepts of colorimetry.
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Red
Purple
P
Reddish orange
Reddish purple
rP
Orange
Purplish red
pR
Orange-yellow
Purplish pink
pPk
Yellow
Pink
Pk
Greenish yellow
Yellowish pink
yPk
Yellow-green
Brownish pink
brPk
Yellowish green
Brownish orange
brO
Green
Reddish brown
rBr
Bluish green
Brown
Sr
Greenish blue
Yellowish brown
yBr
Blue
Olive-brown
0)Br
Purplish blue
Olive
01
Violet
Olive-green
01G
FIGURE 3.15 THE ISCC-NBS HUE NAMES AND ABBREVIATIONS FOR
A CONSTANT MUNSELL VALUE OF SIX (Judd and
Wyszecki, 1963; Judd and Kelly, 1955)
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FIGURE 3.16 THE ISCC-NBS MODIFIERS FOR A PURPLE HUE
(Judd and Wyszecki, 1963)
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3.4.1 Instrumental Colorimetry
The primary objective of instrumental colorimetry is to determine
the CIE tristimulus values X, Y, and Z (see 3.3.2 CIE COLOR SYSTEM) for a
given transparent or opaque sample. These CIE tristimulus values are used
to calculate the CIE chromaticity coordinates x and y for the color of the
sample. Two of the instruments frequently used in colorimetry are the
RECORDING SPECTROPHOTOMETER and the TRISTIMULUS COLORIMETER. The. spectro-
photometer is used to measure the spectral reflectance of opaque samples
or the spectral transmittance of transparent samples. These measured
values for the spectral transmittance or the spectral reflectance of the
sample are used in calculating the CIE tristimulus values for the color
of that sample. Colorimeters, on the other hand, are designed to measure
directly the approximate CIE tristimulus values for the color of a sample.
3.4.1.1 Recording Spectrophotometer
The functional design of a recording SPECTROPHOTOMETER is
diagrammed in Figure 3.17. The light sources used in these instruments
emit electromagnetic radiation in the visible, near-ultraviolet, and
near-infrared portion of the spectrum. Most instruments, have a wave-
length range from 300 to 800 nanometers. The light emitted by the lamp
is collected and directed into the entrance port of the wavelength
selection device by the COLLIMATION OPTICS. The wavelength-selection
device is a prism or a diffraction grating* that rotates and sweeps light
of various wavelengths across the narrow slits in front of the sample.
The width of this opening is adjusted to pass a 5 to 10-nanometer band
of light, thus, illuminating the sample with a collimated beam of nearly
monochromatic light. A transducer connected to the prism or grating
generates an electrical signal proportional to the rotation of the prism
or grating, hence proportional to the wavelength of the entering light.
This electrical signal is used to control the horizontal motion of the
pen or an x-y recorder. The light that passes through the sample is
collected and focused onto the surface of the light detector whose
electrical signal is proportional to the amount of light that is being
transmitted by the sample. When the signal from the light detector is
used to control the vertical motion of the pen of an x-y recorder, the
pen trace in x is wavelength and that in y is intensity. Thus, the
spectral transmission of the sample is recorded. If an opaque sample
* Both prisms and diffraction gratings are devices for separating or
dispersing light into its components.
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Light source
Light dispersing
Collimation element (prism or
optics grating)
Red light
Wavelength, nanometers
FIGURE 3.17 A SCHEMATIC DIAGRAM OF A SPECTROPHOTOMETER BEING USED
TO MEASURE THE SPECTRAL TRANSMITTANCE OF A SAMPLE
yep F~ o 41
ok, ~/9h Go Cj a
Signal to Y-axis: intensity
X-Y chart
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were being measured, the collection optics would be replaced by an
INTEGRATING SPHERE that would collect most of the light reflected from
the sample. Here, the trace produced on the x-y recorder would be a
record of the reflectance of the sample at each wavelength from 300 to
800 nanometers. The CIE tristimulus values X, Y, and Z would be calculated
from this data. (see:3.3.2).
The functional design of a TRISTIMULUS COLORIMETER is diagrammed
in Figure 3.18. The light emitted by the lamp is collected by the
COLLIMATION OPTICS and projected onto the colored sample. Below the
collimating optics is a set of three filters that can be individually
placed in the beam of light that is being projected onto the sample. The
SPECTRAL ENERGY DISTRIBUTION of the light reaching the sample is the
combination of the spectral properties of the light source and the spectral
transmittance of the particular filter that is in the beam of light. The
light that is reflected from the sample is collected and focused onto the
light detector. The spectral energy distribution of the light reaching
the light detector is a combination of the spectral energy distribution
reaching the sample and the spectral reflectance of the sample. Like the
human eye, the light detector in the tristimulus colorimeter does not
respond equally to all wavelengths; it too has a characteristic spectral
response. The strength of the electrical signal generated by the. light
detector is proportional to the sum or integral of the combined product
(wavelength by wavelength) of the spectral energy distribution reaching
the light detector and the spectral response of the light detector.
In a tristimulus colorimeter the spectral properties of the
filters, the light source, and the light detector are selected so that on
a wavelength-by-wavelength basis their combined spectral properties are
equal or nearly equal to some linear combination of the products formed
separately by the three color-matching functions and one of the CIE
standard sources. Thus, these colorimeters are designed so that the CIE
tristimulus values X, Y, and Z are related to the strength of the signals
that are received when each of the three filters are in the projected
beam of light.
3.4.2 Visual Colorimetry
VISUAL COLORIMETRY includes all those color-measuring procedures
or methods that require an observer who has normal color vision to use his
judgment as to whether or not two colors are identical under a given set of
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viewing conditions. To increase the accuracy and precision of such visual
color-matching techniques, viewing conditions for the observer are specified
and carefully controlled. In a typical visual colorimeter, the observer's
viewing conditions are controlled by restricting not only the elements in
his field of view, but also its size. The observer's field of view is
usually divided into two symmetrically shaped sections, one-half is filled
with light of an unknown color designation and the other half (the
comparison field) is filled with a series of known colors. The observer
adjusts the color of the comparison field until it visually matches the
unknown color. The unknown color then identified as the known color in
the comparison field. VISUAL TRISTIMULUS COLORIMETERS are designed so
that the CIE tristimulus values X, Y, Z, for the color of comparison field
can be readily determined by knowing the amount of light or combination of
filters that the subject used to match the unknown color. The CIE
chromaticity coordinates for the unknown color can be readily calculated
once these tristimulus values are determined.
In some visual colorimeters, the color of the comparison field
can be adjusted to produce a continuous range of colors. That is, the
dominant wavelength, purity, and lightness (see Section 3.3.2) of the
comparison field can be varied independently over a wide range of values.
Other visual colorimeters are designed so that color, i.e., dominant wave-
length, purity, lightness, can be varied only in small but discrete steps.
In such a device, the color of the comparison field is controlled by a set
of filters whose colorimetric characteristics vary in a desired manner.
3.4.3. Treatment of Colorimetric Data and Error Analysis
In colorimetry, the treatment of experimental data and error
analysis is a critical aspect of a research project. The problem is
compounded both by the extreme sensitivity of the eye to slight differences
in color and by the difficulty in doing very accurate and precise
PHOTOMETRY. In too many cases, the eye can detect a difference between
two colors that are measured as being identical. The eye can detect the
difference between two colors that differ by 0.2 of the CIE COLOR-
DIFFERENCE UNIT. By using this value as a measure of the color sensitivity
of the eye to color differences and standard error-analysis and error-
propagation techniques, the effect of experimental errors on the color
measurement process is determined.
A colorimeter or spectrophotometer should have the following
properties if its performance is to equal or exceed the human eye. The
range of wavelengths used at any one time to illuminate the sample should
be less than 7.0 nanometers. For the instrument to equal the performance
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of the eye, its systematic wavelength errors should be less than 0.2
nanometer and its random wavelength errors should be less than 0.3
nanometer. Experimental errors in measuring reflectance or transmittance
of a sample should be less than 0.4 percent if the errors are independent
of both the wavelength and the optical properties of the sample. If the
spectrophotometric errors are not independent of these factors, then the
specified tolerances should be considerably less. For such precision and
accuracy to be maintained, the CIE tristimulus values should be calculated
by using a summation interval of not more than 10'nanometers. In general,
these are very stringent requirements and they are fulfilled only by very
careful experimenters using the very best equipment.
An understanding and appreciation of the nature and magnitude of
colorimetric errors is important to the Center and the interpretation of
aerial color photography. For example, if the colors of two images were
measured to be identical and several of the photointerpreters could detect
a difference between them, there could be considerable time and effort
wasted in debating whether the instrument or the interpreters were correct.
(Both of them could be correct if the nature and the magnitude of the
colorimetric errors were taken into consideration and properly interpreted.)
One of the most confusing and difficult problems in work with
colors is that a given pair of colors will match under one set of viewing
or measuring conditions, but may not match under another slightly different
set of viewing or measuring conditions. This phenomenon of color matching
is called METAMERISM and the colors that behave in this manner are called
METAMERIC PAIRS. Metameric pairs occur when two samples with different
spectral reflectance curves have the same chromaticity coordinates (see
3.3.2 CIE Color System). The spectral reflectance curves (hypothetical in
this example) for the two samples in Figure 3.19 are quite different, but
their CIE tristimulus values are the same. Thus, they form a metameric
pair when illuminated by light from the CIE standard source C but appear
to be quite different when illuminated by light from the CIE standard
source A. The spectral energy distribution for CIE light sources A and C
are shown in Figure 3.20. The magnitude and direction of this color shift
is plotted on the CIE diagram in Figure 3.21. Metamerism is caused by the
summation or integration process that occurs in the human visual mechanism
and colorimetric calculations. A met:americ pair is formed when the sums
or integrals of the products used in the CIE calculations are equal but the
individual terms in the summation or integration are different. By analogy,
2 plus 3 equals 4 plus 1, but neither 2 nor 3 is equal to either 4 or 1.
Thus sets [2,3] and [4,1] form a metameric pair of numbers under addition.
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4-
a)
X-X-X Sample I
~--~-~ Sample 2
I I 1 1
500 600 700 800
Wavelength,nanometers
FIGURE 3.19 THE SPECTRAL REFLECTANCE CURVES
FOR A METAMERIC PAIR OF COLORS
I I I I
500 600 700 800
Wavelength,nanometers
FIGURE 3.20 THE SPECTRAL ENERGY DISTRIBUTIONS FOR
THE CIE STANDARD SOURCES A AND C
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2 .3 .4
x
FIGURE 3.21 THE SHIFT IN THE CIE CHROMATICITY COORDINATES
OF A PAIR OF METAMERIC COLORS PRODUCED BY
CHANGING FROM CIE STANDARD SOURCE C TO CIE
STANDARD SOURCE A
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INSTRUMENTAL METAMERISM is caused by an instrument measuring two different
colors as the same. GEOMETRIC METAMERISM occurs when the colors of two
samples match at one viewing angle, but not at another viewing angle.
Geometric metamerism is usually caused by differences in the surface
texture or internal structure of the colorant layer.
Metamerism is not expected to be a problem for photointerpreters
who are viewing color imagery on a light table illuminated by a white light
that is composed of all the different wavelengths in the visible spectrum.
However, if the illumination source used for the light table creates white
light by combining only a few nearly monochromatic colors, then metamerism
may occur.
In general, all members of a group of color-matching experts will
not agree that a color match exists between two identical samples. Further-
more R. M. Evans (Evans, 1948) estimates that a perfect match between two
colors by an average color-normal observer would probably be unsatisfactory
for 90 percent of all other observers.
Because of the obvious commercial importance of specifying the
tolerance of variance from an items standard color before it is
unacceptable to the customer, many methods have been developed for
specifying and calculating the perceptual differences between colors. In
principle, all methods determine the perceptual difference between the
two colors in a manner similar to the way the geometrical distance between
two points is determined. Similarly, the various color-difference formulas
can be used to calculate the "perceptual distance" between two points, i.e.,
two colors, in a color space. For example, the conspicuousness of two
colors (color conspicuity) may be defined as the magnitude of this
perceptual distance between two colors. The size of the units that are
used to express the "perceptual distance" between any two colors is
usually selected so that one unit of perceptual distance in a color space
represents a just-perceptible or half-the-time observance difference
between two colors. On the 1931 CIE chromaticity diagram an elliptically
shaped figure is formed by the locus of the points that represent those
colors that differ from a given color by a given number of these color-
difference units. For example, the ellipses in Figure 3.22 represent some
of the color-discrimination ellipses that have been published. (MacAdam,
1942; MacAdam, 1971).
Color-difference formulas used to calculate the perceptual
difference between two colors can be applied to interpreting aerial color
photography. The various color-difference formulas could be used to set
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Note: The ellipses are for a
luminance level of l5 foot-
lamberts
FIGURE 3.22 THE STANDARD DEVIATIONS OF COLOR MATCHES BY OBSERVER PGN,
ENLARGED TEN TIMES ON THE 1931 CIE x, y CHROMATICITY
DIAGRAM (Mac Adam, 1942)
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the permissible working tolerances for each step of the acquisition,
processing, and viewing cycle used in aerial color photography. For
example, the various color-difference formulas could be used to determine
both the magnitude and direction in which the color of an image would shift
if there were a change in the spectral distribution of the lamp used in
the viewing table. Thus the standards for lamps that were acceptable for
light table use might be specified as plus or minus so many color-difference
units (see also: Section 3.4.6). The second and perhaps the most important
application of the concept of color differences to aerial color photography
might be in the area of color contrast or target conspicuity. The
conspicuity of a target increases with the color difference that exists
between the target and its background, and the color contrast of a target
could be given as so many perceptual steps or so many color-difference
units.
3.4.6 Color Rendering and Color-Rendering Indices
The term color rendering is used here as a general expression
for the effect on the color appearances of objects in conscious or sub-
conscious comparison with their color appearance under a reference light
source versus another light source. In this context the color-rendering
properties of a given light source are specified by a COLOR RENDERING INDEX
which is a measure of the degree to which, under specified conditions, the
perceived colors of objects illuminated by a light source conform to the
same objects illuminated by the reference source. (Wyszecki and Stiles,
1967). Thus, the color-rendering indices are intended to be an aggregate
measure of the overall color shifts that may occur when imagery is illumi-
nated by light from a nonreference light source.
The color densitometer is the basic measuring instrument used for
collecting data for studying the various relationships between image colors
and factors that control them. The red, blue, and green optical densities
that are measured are related to the combined optical effect produced by
the cyan, magenta, and yellow dyes deposited to form the image. These
optical densities can be used to determine the overall color balance of
imagery or to determine if any color shifts have occurred in the processing.
The construction of a typical color densitometer is illustrated in Figure
3.23.
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Light source
Heat absorbing filters
Spectrum shaping filters
Filter wheel containing red,
blue, and green filters
Illuminating aperture
Film sample
Collection aperture
Light detector
Density indicator
FIGURE 3.23 A SCHEMATIC DIAGRAM OF A TYPICAL
COLOR DENSITOMETER
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3.5.1 Specular and Diffuse Density
A color densitometer may be designed to measure either SPECULAR
or DIFFUSE DENSITY. The particular density measured by a densitometer is
determined by both the degree of collimation of the light used to illuminate
the sample and by the size of the SOLID ANGLE for which the collection
aperture accepts light that has either passed through the sample or has
been reflected from the sample.
If the incident light is highly collimated and the collection
angle is small, then the densitometer will measure SPECULAR density. If
the incident light is not highly collimated and the sampling aperture
subtends a large solid angle, the instrument will measure DIFFUSE density.
Most standard color densitometers, such as the Macbeth RD-102 and RD-100
measure diffuse density, whereas microdensitometers, such as the Joyce-
Lobel, measure specular density. The values for the specular and diffuse
densities of the same image can be quite different. This difference is
determined by optical properties, i.e., scattering and absorption, of the
image-forming materials. For example, the difference between specular and
diffuse density is much greater for images composed of clumps of silver
particles than it is for DIAZO images that are composed of dye molecules.
3.5.2 Analytical and Integral Densitometry
Color densitometry may be ANALYTICAL or INTEGRAL. Analytical
densitometry is done to determine the properties of the individual colorants
that are used to form the image, and integral densitometry measures
integrated spectral properties of the image without reference to the
individual colorants that compose the image. For example, integral densi-
tometry would be used to determine how much the density of a red image
changes when the processing temperature is increased by a half of a degree.
For this same experiment, analytical color densitometry would be used to
determine the change in relative quantities of the yellow and magenta dyes
deposited to form a red image. The particular subdivisions of both integral
and analytical densitometry are discussed below.
Five types of densities are measured in integral color densi-
(1)
INTEGRAL PRINTING DENSITIES are measured with a color
densitometer whose response approximates the photographic
response of the printing or duplicating material onto which
the original image will be copied. Often, the response of
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the densitometer can not be adjusted to approximate the
photographic response of the printing or duplicating
material. In this event, the integral printing densities
are calculated by substituting the measured values for
the red, green, and blue densities of the image into a
set of linear equations. The coefficients for these
equations are determined by combining information on the
sensitometric properties of the duplication material and
the spectral characteristics of the filters in the
densitometer.
(2) COLORIMETRIC DENSITIES are measured for final images
rather than intermediates in a photographic duplication
process. For example, the densities of images on a
direct-reversal amateur motion picture film should be
expressed as colorimet:ric densities. In measuring the
colorimetric density of an image, the response of the
densitometer should duplicate the colorimetric response
of the CIE standard observer (See also 3.4.1.2).
(3)
VISUAL or LUMINOUS DENSITIES can be used to compare the
density of images even though their colors may be
different. For example, the difference between the
measured values for the visual densities of two images
indicates which of these two images would appear to
be lighter to the CIE standard observer. In measuring
the visual density of an image, the response of the
densitometer should approximate the photopic, i.e., y
response of the CIE standard observer.
(4) ARBITRARY THREE-FILTER DENSITIES are measured by using
a densitometer whose response is not related to any
color or density-measuring convention. Any combination
of filters and phototubes may be selected on the basis
of cost and stability rather than any particular optical
properties they might have. Arbitrary three-filter
densitometers are usually used for production testing
and quality-control work in which the only interest is
in detecting day-to-day changes in the density of the
product and not in relating the density measurements
to some other density measuring convention.
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(5) INTEGRAL SPECTRAL DENSITIES are measured at specific
wavelengths by using a series of nearly monochromatic
light sources in the densitometers. For example, the
435.8-nanometers (blue) and 546.1-nanometers (green)
lines of the mercury spectrum are often used in
conjunction with the 643.8-nanometers (red) line of
the cadmium spectrum. These measured values for the
optical density of an image at well-defined wavelengths
are a set of data that can be related to the fundamental
photographic characteristics of that particular film.
The object of ANALYTICAL COLOR DENSITOMETRY is to provide data
that can aid the photoscientist in determining the behavior of the
individual colorants used to form the images in color films and papers.
Three types of analytical densities from which this type of data can be
extracted are the following:
(1) SPECTRAL ANALYTICAL DENSITIES are used to denote the
optical density of an individual colorant at a
particular wavelength. Spectral analytical densities
cannot be measured directly because each of the
colorants used in color photography has some optical
absorption throughout the visible spectrum. Neverthe-
less, the spectral analytical density of an image can
be calculated by using the values for the integral
spectral densities of the image. This calculation
of the spectral analytical densities assumes that
optical densities of the different colorants are
additive and that the colorants are present in the
same ratio for all density levels. If both these
conditions hold, then the spectral analytical
densities for the colorants forming an image can be
calculated from a set of linear equations and the
measured values for integral spectral densities of
that image.
(2) EQUIVALENT NEUTRAL DENSITIES of a colorant used in a
subtractive color process are defined as the visual
or luminance density it would have if it were
converted to a neutral gray by adding to it the just-
required amounts of the other colorants used in the
process. For example, an image composed of only a
magenta dye deposit would have an equivalent neutral
density of 1.0 if it could be converted to a 1.0
neutral density absorber by adding to it the appropriate
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quantities of the cyan and yellow dye used in that
particular color process. The concept of equivalent
neutral densities is quite useful in indicating how
well the color balance of a particular photographic
material is maintained over a wide range of exposure
levels.
(3) EQUIVALENT NEUTRAL PRINTING DENSITIES of colorants are
defined as the printing densities of neutral colorants
that would be matched by adding to colorants the proper
amount of the other colorants so that their combina-
tion will form three equal red, blue, and green printing
densities. Equivalent: neutral printing densities are
used to specify the density of color negative films or
separation negatives that are to be duplicated by
printing them on another photographic material.
Although the subject of color densitometry may appear to be both
difficult and confusing, it has been thoroughly studied and well reported.
Today's solid-state electronics and other optical equipment provides the
photoscientist with equipment that is more than adequate for most of his
needs. Nevertheless, much of the confusion surrounding color densitometry
is usually caused by not understanding what is being measured and by
improper use of the instruments. The Center's effort in this area should
be to educate the personnel who might: use color densitometers or similar
equipment to understand the limitations of these instruments and to know
what pitfalls might hamper their proper operation.
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Beresford, J., "Instrumental Measurement of Colour", Journal of Oil
Colour Chemistry Association, 53(9), pp. 800-820 (1970).
Berger, A. and Biockes, A., "The Accuracy of Tristimulus Colorimeters
When Measuring Metameric Pairs of Dyings", Color Engineering, 5(3),
pp. 34-39 (1967).
Billmeyer, F. W., Jr., "Comparative Performance of Color-Measuring
Instruments", Applied Optics, 8(4), pp. 775-783 (1969).
Billmeyer, F. W., Jr., "Current American Practice in Color Measure-
ment", Applied Optics, 8(4), pp. 737-750 (1969).
Billmeyer, F. W., Jr. "Metamerism - An Introduction", Color
Engineering, 5(3), pp. 26-27 (1967).
Billmeyer, F. W., Jr. and Saltzman, M., Principles of Color
Technology, 1st ed., Interscience Publishers, New York (1966).
Billmeyer, F. W., Jr., "Precision of Color Measurement With the GE
Spectrophotometer", Journal of the Optical Society of America, 55(6),
pp. 707-717 (1965).
Burnham, R. W., Hanes, R. M., and Bartleson, C. J., Color: A Guide
to Basic Facts and Concepts, Wiley, New York, New York (1963).
Davidson, H. R. and Friede, E., "The Size of Acceptable Color
Difference", Journal of the Optical Society of America, 43(7),
pp. 581-589 (1953).
Dekerf, J.L.F., "Accuracy of Tristimulus Computations", Journal of
the Optical Society of America, 48(5), pp. 334-338 (1958).
Evans, R. M., Hanson, W. T., and Brewer, W. L., Principles of Color
Photography, John Wiley and Sons, New York (1953 .
Evans, R. M., An Introduction to Color, 1st ed., John Wiley and Sons,
New York (1948).
Erhart, F. H., ed., Principles of Color Sensitometry, 2nd ed., Society
of Motion Picture and Television Engineers, New York (1963).
Garra, A. A. and Briggs, S. J., "Image Interpretation State-of-the-
Art Review", The Boeing Company, Aerospace Group, Seattle, Washington
(1970).
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Gourley, J., Rib, H. T., and Miler, R. D., "Automatic Technique for
Abstracting Color Description From Aerial Photography", Photographic
Science and Engineering, 12(1), pp. 27-35 (1968).
Granville, W. C., "Metamerism - A Historical Essay", Color Engineering,
5(3), pp. 28-33 (1967).
Hunt, R.W.G., "Objectives in Colour Reproduction", Journal of
Photographic Science, 18(6), pp.205-215 (1970).
Hunt, R.W.G., The Reproduction of Colour, 2nd ed., Fountain Press,
London (1967).
Ingle, G. W., Stockton, F. D., and Hemmendinger, H., "Analytic
Comparison of Color Difference Equations", Journal of the Optical
Society of America, 52(9), pp. 1075-1077 (1962).
James, T. H., ed., Theory of the Photographic Process, 3rd ed.,
MacMillan Company, New York (1966), "The Sensitometry of Color Films
and Papers", (J. L. Simonds) pp. 450-463.
Johnston, R., "Geometric Metamerism", Color Engineering, 5(3), pp. 42-
47 (1967).
Judd, D. B., "Ideal Color Space", Color Engineering, 8(2), pp. 37-52
(1970).
Judd, D. B. and Wyszecki, G., Color in Business, Science, and
Industry, 2nd ed., John Wiley and Sons, New York (1963).
Judd, D. B., Chamberlin, G. J., and Haupt, G. W., "Ideal Lovibond
Color System", Journal of the Optical Society of America, 52(7),
pp. 813-819 (1962).
Judd, D. B. and Kelly, K. L., The ISCC-NBS Method of Designating
Colors and a Dictionary of Color Names, National Bureau of Standards
Circular 553 (1955).
Judd, D. B., "Reduction of Data on Mixture of Color Stimuli", Bureau
of Standards Journal of Research, 4, pp. 515-548 (1929).
Little, A. C., "Evaluation of Single - Number Expressions of Color
Difference", Journal of the Optical Society of America, 53(2),
pp. 293-296 (1963).
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MacAdam, D. L., "Geodesic Chromaticity Diagram Based on Variances of
Color Matching by 14 Normal Observers", Applied Optics, 10(1),
pp. 1-7 (1971).
MacAdam, D. L., "Color Science and Color photography", Physics Today,
20(1), pp 27-39 (1967).
MacAdam, D. L., "Visual Sensitivities to Color Differences in Day-
light", Journal of the Optical Society of America, 32(5), pp. 247-274
(1942).
MacAdam, D. L., "Subtractive Color Mixture and Color Reproduction",
Journal of the Optical Society of America, 28(12), pp. 466-480
(1938).
MacAdam, D. L., "Photographic Aspects of the Theory of Three-Color
Reproduction", Journal of the Optical Society of America, 28(11),
pp. 399-418 (1938).
McCarley, J. E., Green, C. E., and Horowitz, K. H., "Digital System
for Converting Spectrophotometric Data to CIE Coordinates, Dominant
Wavelength, and Excitation Purity", Journal of the Optical Society
of America, 55(4), pp. 355-360 (1965).
Miller, C. W., "The Matrix Algebra and Color Reproduction", Journal
of the Optical Society of America, 31(7), pp. 477-482 (1941).
Mudd, J. S. and Woods, M., "Colour and Difference Measurement",
Journal of the Oil Colour Chemistry Association, 53(10), pp. 852-875
(1970).
Newhall, S. M., Nickerson, D., and Judd, D. B., "Final Report of the
O.S.A. Subcommittee on the Spacing of the Munsell Colors", Journal
of the Optical Society of America, 33(7), pp 385-418 (1943).
Nickerson, D. and Jerome, C. W., "Color Rendering of Light Sources:
CIE Method of Specification and its Applications", Illuminating
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(1968).
Nimeroff, I., "Comparison of Uncertainty Ellipses Calculated From Two
Spectrophometric Colorimetry Methods by an Automatic-Computer
Program", Journal of the Optical Society of America, 56(2), pp. 230-
237 (1966).
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Nimeroff, I. and Yurow, J. A., "Degree of Metamerism", Journal of
the Optical Society of America, 55(2), pp. 185-190 (1965).
Nimeroff, I., Rosenblatt, J. R., and Danneniller, M. C., "Variability
of Spectral Tristimulus Values", Journal of the Optical Society of
America, 52(6), pp. 685-691 (1962).
Nimeroff, I., "Propagation of Errors in Tristimulus Colorimetry",
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Nimeroff, I., "Propagation of Errors in Spectrophotometric Colorimetry",
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Onley, J. W., "Analytical Densitometry for Color Print Evaluation",
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Powers, S. A. and Miller, I. E., "Pitfalls of Color Densitometry",
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Rheinboldt, W. C. and Menard, J. P., "Mechanical Conversion of
Colorimetric Data to Munsell Rentations", Journal of the Optical
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Richter, M., "The Official German Standard Color Chart", Journal of
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Robertson, A. R., "Colorimetric Significance of Spectrophotometric
Errors", Journal of the Optical Society of America, 57(5), pp. 691-
698 (1967).
Robertson, A. R. and Wright, W. D., "International Comparison of
Working Standards for Colorimetry", Journal of the Optical Society
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Sant, A. J., "Procedures for Equivalent-Neutral-Density (END)
Calibration of Color Densitometers Using a Digital Computer",
Photographic Science and Engineering, 14(5), pp. 356-362 (1970).
Stiles, W. A. and Wyszecki, G., "Counting Metameric Object Colors",
Journal of the Optical Society of America, 52(3), pp. 313-328 (1962).
Yule, J.A.C., "The Theory of Subtractive Color Photography, I. The
Conditions for Perfect Color Rendering", Journal of the Optical
Society of America, 28(11), pp. 419-430 (1938).
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Yule, J.A.C., "The Theory of Subtractive Color Photography, II.
Prediction of Errors in Color Rendering Under Given Conditions",
Journal of the Optical Society of America, 28(12), pp. 481-492
(1938).
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Diagram", Journal of the Optical Society of America, 46(11), pp. 982-
986 (1956).
Wyszecki, G., "Propagation of Errors in Colorimetric Transforms",
Journal of the Optical Society of America, 49(4), pp. 389-393 (1959).
Wyszecki, G., "Recent Agreements Reached by the Colorimetry Committee
of the Commission Internationale de 1'Eclairage", Journal of the
Optical Society of America, 58(2), pp. 290-292 (1968).
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of the Optical Society of America, 59(2), pp. 123-125 (1969).
Wyszecki, G. and Stiles, W. S., Color Science, 1st ed., John Wiley
and Sons, New York (1967).
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A knowledge of the principles and concepts of color photography
will be more useful to the image interpreter as a communication tool than
as an aid in helping him find and identify more targets in a shorter period
of time. The basic theory of color photography is not of great interest
to the image interpreter, because he is concerned primarily with imagery and
not with all the other aspects of small-scale, high-resolution color photo-
graphs. Therefore, the physical properties and photographic characteristics
of color films and how these properties and characteristics are related and
manipulated are of little use to the interpreter. Nevertheless, a signifi-
cant portion of an image interpreter's time is spent communicating with
those individuals and organizations that levy requirements on him and that
supply support services to him. If an interpreter can clearly communicate
his film-related needs and problems to these individuals and organizations,
they can probably perform their jobs more efficiently and productively.
Although the following discussion of the construction of color
films and the physical properties used in the design of these films is
limited to high-resolution, color-reversal acquisition films, such_ as
Eastman Kodak's SO-255, the general principles that are discussed are
applicable to a great variety of color films. It is assumed in the follow-
ing discussion of color-film theory t'aat the reader is familiar with the
subtractive process of color reproduction as explained in Section 3.2.2 of
this report. Thus, the main emphasis is placed on the formation of cyan,
magenta, and yellow dyes in proper proportion and location in the film,
rather than why the dyes are used for a color film.
The general configuration of a color film is shown in Figure
4.1. A typical color film consists of a "tripack" or three-layer emulsion
coated on a chemically suitable and dimensionally stable base such as glass
or mylar. Each layer of the tripack contains both light-sensitive, image-
forming SILVER HALIDE materials and nonlight-sensitive, color-forming
materials dispersed in a gelatin-based carrier. This dispersion of
materials in the gelatin carrier is indicated by the small squares and
circles in the figure. The light-sensitive, image-forming silver halide
materials in each layer of the tripack are chemically sensitized so that
they respond only to light from a desired part of the visible spectrum.
Similarly, the color-forming materials or DYE COUPLERS in each layer of
the tripack emulsion produce only a dye of a single color when they are
Color-reversal films produce a positive color image of the scene to
which they were initially exposed.
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Spectral
Sensitivity Curves
Light-Sensitive
Image-Forming
Silver Halide Materials
A Piece of
Color Film
0000000000
q
. 0 00^ c~^0 _E1 c
~ r'r^c^c c c w
Nonlight Sensitive
Color-Forming Materials
(i.e., dye couplers)
Spectral Transmittance Curves
for the Dyes Formed by the
Dye Couplers
UL
500 600 700 0
400
400 500 600 700 400 500 600 700
Wavelength, nanometers Wavelength, nanometers
000 0C3 0
00000^0110^
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activated during development. The spectral-sensitivity curves for the
light-sensitive, image-forming silver halide materials and the spectral
transmittance curves for the colors resulting from a given concentration
of dye are shown on the right side of: the figure. Note that the color
formed by a dye coupler in a given layer is the complementary color" of
that to which the image-forming material is sensitive. When an exposure
is made, the image-forming silver halide materials in each of the layers
respond to their appropriate components in the scene. In this way, the
invisible LATENT IMAGE formed in the three layers is a record of the
spatial distribution of the various color components in the scene. When
the exposed film is developed, these latent images become visible and
some of the chemical by-products of this development reaction combine with
the dye couplers to form the cyan, magenta, and yellow globules of dye.
The amount of dye formed in an area is proportional to the concentration of
the developer by-products in that particular region. Before the processing
is completed, the silver images that represent the red, blue, and green
records of the scene are removed from the tripack emulsion by a chemical
bleach that forms a soluble silver compound. A positive dye image of the
original scene remains. Thus, this type of color photography consists of
using the chemical by-products formed in a development reaction to control
the formation of the cyan, magenta, and yellow dyes.
Although the basic concept can be applied to either negative-
working or positive-working films, the following discussion is limited to
the color-reversal films. The image colors produced by a negative-working
film are the COMPLEMENTARY colors of those in the original scene. For
example, green marking on the tail of an aircraft will appear as green on
a color-reversal film, and as magenta (the complement of green) on a
negative-working film.
The physical configuration of a color-reversal film is illus-
trated at the top of Figure 4.2. The small squares indicate the light-
sensitive image-forming silver halide materials and the small circles
indicate the nonlight-sensitive color-forming materials which are dispersed
in each layer of the tripack emulsion. The spectral-sensitivity region of
each emulsion layer is shown at the trop right of the drawing and the colors
of the dye formed when the dye couplers are activated is shown at the top
left of the drawing. The following discussion of the formation of the
colored image in a color-reversal material begins with the exposure of the
film in an image-forming optical system, e.g., a camera, and concludes
with the formation of the dye image that is ready for use by the image
interpreter.
Complementary colors are pairs of colors, which when mixed in suitable
proportions, match some agreed upon achromatic color.
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White
Dye color
Magenta
Cya n
Yellow
Exposure and latent image formation-Step 1
Black
^O^O^
00000
O^o^o
00000
000oo
00000
0ooao
00000
ooooo
00000
o^O^O
00000
o0o0a
00000
00000
00000
00000
00000
0o0o0
a0o0o
00o0o
00000
00000
00000
^0^0^
00000
00000
E0HI0E
^0^0^
00000
0^0^0
00000
00000
000O0
0^0^0
00000
Black and White development - Step 2
^0^0^
O^O^O
0^0^0
^O^O^
^0^0^
O^O^O
0^0^0
^O^O^
^0^0^
O0000
0^0^0
00000
^0^0^
00000
0^0^0
00000
^0^0^
00000
0^0^0
00000
^0^0^
00000
0^0^0
00000
^O^0^
O^O^O
0^0^0
^O^O^
^0^0^
O^O^O
0^0^0
^O^O^
^0^0^
O0000
0^0^0
00000
Color development - Step 3
^?^?^
00000
?^?^?
00000
^0^00
00000
0000O
000?0
^0^O^
0^O^O
?^?^?
^0000
00000
00000
00000
00000
00000
00000
00000
00000
00000
00000
00000
00000
^0^0^
0^0^0
0^0^0
^0^O^
^0^0^
0^0^0
0^0^0
^O^00
^0^0^
0^0^0
0^0^0
^0^0^
Bleach and stabilization - Step 4
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Reproduction of original scene
White
Block
Spectral
sensitivity
Green
FIGURE 4.2 THE FORMATION AND DEVELOPMENT OF A COLORED IMAGE IN A
COLOR-REVERSAL PHOTOGRAPHIC PROCESS.
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It is assumed that the film is exposed in a camera that is
focused on the colored target shown at the top center of Figure 4.2. The
latent images that are formed as a result of this exposure to ACTINIC LIGHT
are indicated by the small black dots inside the small squares. These
images are formed as a result of a photochemical reaction between the
incident light and the image-forming silver halide materials. The number
of metallic silver nuclei contained in each of the latent images is pro-
portional to the effective exposure received by that particular area of
the emulsion. The latent images formed in the three layers of the emulsion
record the spatial distribution of the red, blue, and green colors of the
objects in the scene. For example, the latent images that were formed in
the red-sensitive middle layer of the tripack emulsion is the record of the
spatial distribution of the red component of the red, orange, and white
colored areas of the target. Similarly, the latent images that were formed
in the blue- and green-sensitive layers are the records of the blue and
green colors of the various target areas. A latent image is formed in each
layer of the tripack emulsion which corresponds to the red, blue, and green
components of the light coming from the white target. For example, the
latent images of the orange target shown in Figure 4.2 appear in both the
red- and green-sensitive layers of the tripack emulsion; this composite
latent image of the orange-colored target contains many more silver
particles in the red-sensitive layer than it does in the green sensitive
layer. In a similar manner, the spatial distribution of all the colors in
the scene are recorded as latent images in the three layers of the tripack
emulsion. In order for these latent images to be useful to the inter-
preter, they must be rendered visible by processing them in the appropriate
chemical solutions.
The exposed film is processed in a conventional black and white
developer. When the exposed film is immersed in the developer, each of the
metallic silver nuclei that composed the latent image acts as a catalyst
for the development reaction. One of the reaction products is a large
cloud of easily visible clumps of metallic silver located at or near the
nuclei that initially catalyzed the reaction. The formation of these
large clumps of metallic silver is indicated by the black squares shown
as following Step 2 (Figure 4.2). If the film is viewed at this stage of
development, a negative black and white image of the original scene is
seen. The area of the image that corresponds to the black target, being
devoid of clumps of silver, appears as a light area when viewing the film
in white light. Conversely, the area on the film that corresponds to the
white target, being completely filled with clumps of silver, appears as a
dark area on the film when viewed in white light. Note that the
unblackened squares in the drawing indicate image-forming material not
consumed by the development reaction. Also, the uncolored circles indicate
that the dye couplers have not reacted in this development step with the
chemical by-products of the development reaction to form blobs of cyan,
magenta, and yellow dyes.
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The color-development step (Step 3 in Figure 4.2) is used to
create a correctly colored positive dye image from the black and white,
negative, silver-based image. After it is rinsed to remove black and
white processing chemicals from the emulsion, the partially developed film
is placed in a solution of color developer. Some of the chemicals in the
color-developer solution react with the image-forming silver halide mate-
rials that were not developed by the "black and white" or the first
developer. Such a development process is usually called a REVERSAL
DEVELOPMENT process because large clumps of metallic silver are now formed
in those areas that did not receive actinic light.
The chemical by-products of this reversal development step react
with the other chemicals in the color-developer solution and with the dye
couplers in the emulsion to form blobs of the appropriate subtractive dyes
at or near those areas at which the reversal development produced clumps
of metallic silver. The color, concentration, and location of the silver
and dye images are shown in the drawing that follows Step 3 (Figure 4.2).
The concentration levels of the dye blobs, which are shown as cyan,
magenta, and yellow circles in Figure 4.2, are proportional to the con-
centration levels of the chemical by-product produced by the reversal
development.
At this point in the overall development process, the image-
forming silver halide material is converted to clumps of metallic silver.
This uniformly dense silver image would completely obscure the color-
positive dye image in the tripack emulsion. The final steps in developing
color-reversal film are to chemically remove all the clumps of silver and
unused dye coupler from the emulsion and to chemically stabilize the dyes.
The final dye image is shown at the bottom of Figure 4.2. When this image
is viewed over white light, the effects of the various dye layers combine
to reproduce the proper target colors.
Table 4.1 is a listing of selected photographic properties of
some aerial color films that might be of interest. The basic photographic
theory of these types of materials is discussed in Section 4.1 COLOR-FILM
THEORY. (Smith, 1968; and Eastman Kodak Publication M-70).
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Manufactur
Aerial
Resolving Power, lines/mm
er
Film N
mb
Exposure
RNS
u
er
Index
1000:1
1.6:1
Granularity
Processi
Aerocolor
Negative
Eastman Kodak;
2445
High-speed color negative film for mapping and
reconnaissance
32
80
40
14
ng
Aero-Neg Color
Process
Ektachrome
MS Aero-
graphic
Eastman Kodak;
2448
Color-reversal film for low to medium altitude
aerial mapping and reconnaissance
Aerial Color
Eastman Kodak;
SO-242
Slow-speed, high-resolution film for high-altitude
reconnaissance
2
200
100
11
Kodak Process
ME-4 (modified)
Aerial Color
Eastman Kodak;
S0-255
Similar to S0-242; ultra-thin base for maximum spool
capacity; high-resolution film for high-altitude
reconnaissance
2
200
100
11
Kodak Process
ME-4 (modified)
Ekachrome EF
Aerographic
Eastman Kodak;
S0-397
High-speed, color-reversal film for aerial mapping
and reconnaissance
12
63
32
i5
EA-4; EA-5
Acrochrome EF Eastman Kodak; Similar to S0-397
SO-154
Anscochrome General Aniline High-speed, high-contrast color reversal film for
and Film aerial photography
Corporation;
D 200
Anscochrome General Aniline Very high-speed, high-contrast color reversal film
and Film and aerial photographs
Corporation;
D 500
Aerial Eastman Kodak; Low-contrast, color-reversal film for making dupli-
Ektachrome R SO-118 cate transparencies from aerial Ektachrome and
Print Acrochromc film originals
Aerial Color Eastman Kodak; High-contrast, color reversal film for making
Duplicating SO-271 duplicate transparencies from aerial Ekachrome
and Aerochrome film originals
Aerographic S0-360 duplicate transparencies from Ektachrome and applicable
Duplicating Aerochrome film originals; high dimensional
stability
Anscochrome General Aniline A duplicating film for duplicating Anscochrome Not
Duplicating and Film D 200 and D 500 color aerial film applicable
Film Corporation;
T-6470
wpucacnng and Film material
Film Corporation;
T-7470
Not 100 50 9
applicable
Not 80 50 8.5 EA-5; EA-4
applicable
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FALSE COLOR or CAMOUFLAGE DETECTION color film is another type of
color aerial film that may be of interest to the image interpreter because
of its possible future use for solving very special and unique detection
and identification problems (see 5.1.3.2 Color Infrared Film). The concept
of false-color aerial film is quite similar to that for color-reversal or
"true color" aerial films because for both films,'the chemical by-products
of a development reaction are used to control the formation of various
colored dyes. The difference between false-color films and the true-color
films is the spectral response characteristics of each of the individual
layers of the tripack emulsion. The true-color films respond to the red,
blue, and green portions of the spectrum whereas the false-color films
respond to the green, red, and INFRARED* portions of the spectrum**. The
spectral sensitivity of each of the false-color films are as follows: the
yellow dye-forming layer responds to green light, the magenta dye-forming
layer to red light, and the cyan dye-forming layer to "infrared light"** .
The colors of objects in imagery that was acquired with false-color film
are quite different from their natural color because of the altered
spectral response of the dye-forming layers:
? Reds, or combination of colors containing red, turn yellow
or predominantly yellowish.
? Greens, or combinations of color predominantly green, turn
violet.
The infrared portion of the spectrum to which false-color film is
sensitive extends from approximately 700 to 900 nanometers.
** False-color or camouflage detection film also is sensitive to blue
light because the infrared sensitizing dye that is used to sensitize
the cyan dye-forming layer also produces a significant amount of blue-
light sensitivity in the same layer. A yellow-colored or minus-blue
filter used during acquisition absorbs most of the blue light in the
image. Thus, the effective sensitivity of the false-color fi:Lm is in
the green, red, and infrared portions of the spectrum.
*** Strictly speaking, infrared radiation is not light, because such long
wavelengths fall outside of what is usually considered to be the visual
response range of the eye. By common usage those electromagnetic radia-
tions only slightly longer than the longest visible wavelengths are
referred to as infrared light.
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? Yellows, or combinations of colors which are predominantly
yellow, turn to a near white, often with a faint green cast.
? Blues, or combinations of colors where blue is the predominant
color, remain blue, but of a darker shade.
? Browns (burnt umber and sienna brown) turn dark green and
light green, respectively.
? Violet and violet-blue-violet turn orange and dark brown,
respectively.
? Gray scales appear in varied shades of blue since not all
the blue light is filtered out by the yellow filter.
For example, natural vegetation appears as red in imagery that was acquired
with a false-color film, because natural vegetation reflects "infrared
light" as well as green light. However, objects painted with a green paint
that does not reflect a significant amount of infrared wavelengths will
appear to be violet on a false-color film. Similarly, a natural brown
color, which is a desaturated orange, appears as green. The overall result
of false-color imagery is to shift the colors of objects so that manmade
targets can be readily distinguished from their natural surroundings.
(Smith, 1968).
4.2.3 Spectrazonal or Multispectral Film and Techniques
Spectrazonal or multispectral photography is intended to exploit
the unique spectral reflectance properties or color signatures of a given
class of targets (see 5.1.3.4 Spectrazonal or Multispectral Techniques).
The basic concept is to optically remove all wavelengths except those that
are related to a specific type of target. Thus, in theory, spectrazonal
photography is a way to increase the color contrast between a target and
its background. Spectrazonal or multispectral imagery is acquired by
having multiple cameras on the same acquisition platform or multiple
lenses on one camera. All lenses are identical as nearly as possible and
each is fitted with a filter with a different color (broad band pass or a
very narrow band pass depending on target being photographed). For
example, of two cameras in use, one might be equipped with a red filter,
and the other with a blue filter. Conventional panchromatic, black and
white, or silver halide film can be used in both cameras. The multi-
spectral imagery is acquired by simultaneously exposing the film in both
cameras to the same scene. Thus, both red and blue records of the scene
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are obtained. Spectrazonal photography has demonstrated that the targets
of interest may be more evident on the film used for one color than on the
other colors.
4.2.4 Additive Color Separations
The additive method of aerial color photography has seen very
limited use because of the cost and the optical complexity of the 3-camera
system, and the 3-projector replay system. The principal features of the
additive color reproduction process are discussed in Section 3.2.1 and its
problems in Section 5.1.3.3.
4.3 EFFECTS OF TARGET AND ACQUISITION PARAMETERS ON COLOR AERIAL
PHOTOGRAPHY AND COLOR PERCEPTION
4.3.1 Colorimetric Properties of Selected Natural and
Man-Made Targets
Color coordinates of various targets are tabled so that the
Center's personnel can gain some appreciation of where various targets are
located in both the CIE and Munsell color space. CIE and Munsell designa-
tions for the colors of some selected natural and man-made objects are
given in Tables 4.2 and 4.3, respectively, and CIE chromaticity coordinates
are plotted in Figure 4.3. Although exceptions exist, the following
generalization about these colors can be very helpful in considering the
effects of the atmosphere on color imagery. The colors of these selected
natural and man-made targets have CIE dominant wavelengths in the 560 to 590
manometers region of the spectrum and Munsell hues in the green-yellow to
yellow-red sector of the Munsell hue circuit. The CIE lightness of many
of these colors is less than 30 percent and their corresponding Munsell
values are less than 6. The colors of these targets are usually low in
saturation, typical CIE excitation purity is less than 50 percent and
typical Munsell chroma is less than 3. Thus, the majority of the targets
that might appear in color imagery are usually a dull, greenish-brown
color. Obviously, there are exceptions to these generalizations. The
manner in which the atmosphere distorts both the geometrical shape and
color of these targets is discussed in the following section of the report.
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FIGURE 4.3 CIE CHROMATICITY COORDINATES FOR SELECTED NATURAL
AND MAN-MADE TARGETS
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TABLE 4.2 THE CIE CHROMATICITY COORDINATES, LIGHTNESSES, DOMINANT WAVELENGTHS AND
EXCITATION PURITIES FOR THE COLORS OF SELECTED NATURAL AND CULTURAL TARGETS
Type of
Chromaticity
Coordinates
Lightness
Value
Dominant
Wavelength
Excitation
Purity
CIE Standard
Sample
x
y
Y, %
X d nm
Pe, %
1.
Inland water
0.269
0.289
5,0
481.0
31.0
B
2.
Snow, fresh fallen
0.340
0.346
77.0
481.0
3.0
B
3.
Snow, covered with ice
0.351
0.354
75.0
579.5
2.0
B
4.
Limestone, clay
0.377
0.376
63.0
579.0
18.0
B
5.
Mountain tops, bare
0.399
0.387
24.0
581.6
29.0
B
6.
Sand, dry
0.399
0.387
24.0
581.6
29.0
B
7.
Clay, soil, wet
0.382
0.373
9.0
582.8
18.0
B
8.
Ground, bare, rich soil, dry
0.382
0.373
9.0
582.8
18.0
B
9.
Ground, black earth, sand, loam
0.377
0.369
3.0
583.2
15.0
B
10.
Coniferous forest, winter
0.381
0.396
3.0
574.4
25.0
B
11.
Coniferous forest, summer
0.397
0.410
8.0
575.8
36.0
B
12.
Meadow, dry; grass
0.397
0.410
8.0
575.8
36.0
B
13.
Deciduous forest, summer
0.394
0.432
10.0
571.9
43.0
B
14.
Grass, lush
0.394
0.432
10.0
571.9
43.0
B
15.
Deciduous forest, fall
0.451
0.399
15.0
585.8
50.0
B
16.
Field crops, ripe
0.451
0.399
15.0
585.8
50.0
B
17.
Earth roads
0.377
0.369
3.0
583.2
15.0
B
18.
Black top roads
0.382
0.373
9.0
582.8
18.0
B
19.
Buildings
0.382
0.373
9.0
582.8
18.0
B
20.
Wet White Sand, Rodger's Quarry
0.359
0.356
21.8
580.4
23.7
C
21.
Wet Yellowish Quartz Sand, Rodger's
0.392
0.373
21.0
582.7
37.2
C
Quarry
22. Wet Commercial (Zonalite)
0.354
0.348
16.5
582.0
20.3
C
"Vermiculite"
23. Dry White Sand, Rodger's Quarry
0.350
0.349
37.7
580.3
19.5
C
24. Dry Yellowish Quartz Sand, Rodger's
0.373
0.363
36.9
581.6
29.4
C
Quarry
25. Dry Commercial (Zonalite)
0.337
0.337
27.7
580.0
13.0
C
"Vermiculite"
26. Damp Collington Sandy Loam
0.349
0.345
14.9
582.0
18.0
C
27. Outer Bark, Scrub Pine (Pinus
0.358
0.346
11.9
584.2
20.8
C
virginiana, Mill.)
28. Inner Bark, Scrub Pine (Pinus
virginiana, Mill.)
O..siz
0.349
14.7
586.4
25.4
C
29. Outer Bark, White Oak (Quercus alba,
0.326
0.342
27.7
571.1
11.1
C
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TABLE 4.2 THE CIE CHROMATICITY COORDINATES, LIGHTNESSES, DOMINANT WAVELENGTHS AND
EXCITATION PURITIES FOR THE COLORS OF SELECTED NATURAL AND CULTURAL
TARGETS (Continued)
Type of
Chromaticity
Coordinates
Lightness
Value
Dominant
Wavelength
Excitation
Purity
Sample
x
y
Y, 2
>1 d nm
Pe, %
30.
Inner Bark, White Oak (Quercus alba,
0.357
0.350
7.5
580.2
23.1
31.
L.)
Chinese Red #6335 Chi-namel Paint,
0.556
0.330
16.5
609.4
69.5
Chi-namel Paint and Varnish Co.
32. Colony Yellow #317 House Paint,
0.379
0.391
68.5
576.5
38.4
Lowe Brothers
33. Green #173 Tractor Paint, Lowe
0.268
0.339
6.8
497.6
14.2
Brothers
34. Red #139 Tractor Paint, Lowe
0.514
0.321
10.7
613.2
55.8
Brothers
35. Royal Blue Permanent Trim Paint,
0.221
0.234
10.0
478.8
41.6
John W. Masury & Son
36. Sea! Brown Supreme House Paint, 0.378
0.343
8.2
590.3
25.4
John W. Masury & Son
37. Verdi Green #6830 Super House Paint,
0.256
0.400
30.7
511.1
18.6
Chi-namel Paint and Varnish Co.
38. Khaki #1 (cotton) 0.368
0.366
24.7
579.7
28.9
39. Olive Drab #52 (wool) 0.378
0.379
10.3
578.6
35.1
40. US Marine Corps Necktie 0.371
0.362
19.9
581.6
28.5
41. US Marine Corps Overseas Cap (summer) 0.377
0.371
19.0
580.4
32.7
42. US Marine Corps Pants (summer) 0.368
0.364
21.6
580.3
28.3
43. US Marine Corps Shirt (summer) 0.368
0.372
23.2
578.2
30.4
44. US Marine Corps Overseas Cap (winter) 0.329
0.345
5.4
572.0
12.8
45. US Marine Corps Blouse (winter) 0.327
0.347
5.3
569.7
12.8
46. US Marine Corps Pants (winter) 0.329
0.344
6.0
572.3
12.5
CIE Standard
Source
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TABLE 4.3 THE MUNSELL AND ISCC-NBC DESIGNATIONS FOR THE COLORS OF
SELECTED NATURAL AND CULTURAL TARGETS
Type of
ISCC-NBS Color
Sample
Designations
20.
Wet White Sand, Rodger's Quarry
0.2Y
5.2/2.3
Grayish yellowish brown
21.
Wet Yellowish Quartz Sand, Rodger's Quarry
8.6YR
5.1/3.7
Moderate yellowish brown
22.
Wet Commercial (Zonalite) "Vermiculite"
9.2YR
4.6/1.8
Grayish yellowish brown
23.
Dry White Sand, Rodger's Quarry
9.8YR
6.6/2.2
Light grayish yellowish brown
24.
Dry Yellowish Quartz Sand, Rodger's Quarry
8.9YR
6.6/3.6
Light yellowish brown
25.
Dry Commercial (Zonalite) "Vermiculite"
9.OYR
5.8/1.3
Light grayish yellowish brown
26.
Damp Collington Sandy Loam
9.6YR
4.4/1.5
Grayish yellowish brown
27.
Outer Bark, Scrub Pine (Pinus virginiana,
Mill.)
8.OYR
4.0/1.7
Grayish yellowish brown
28
Inner Bark
Scrub Pine (Pinus vir
iniana
.
g
,
,
Mill.)
29.
Outer Bark, White Oak (Quercus alba, L.)
O.9GY
5.8/1.1
Light olive gray
30.
Inner Bark, White Oak (Quercus alba, L.)
9.7YR
3.2/1.5
Dark grayish yellowish brown
31.
Chinese Red il6335 Chi-namel Paint,
Chi-namel Paint and Varnish Co.
7.2R
4.6/13.3
Vivid Reddish orange
32
Y
P
C
l
ll
#317 H
i
t
.
o
ony
e
ow
ouse
a
n
,
Lowe Brothers
33.
Green #173 Tractor Paint, Lowe Brothers
0.8BG
3.1/2.9
Dark bluish green
34.
Red #139 Tractor Paint, Lowe Brothers
5.9R
3.8/9.8
Moderate red
35.
Royal Blue Permanent Trim Paint,
John W. Masury & Son
2.1PB
3.7/5.6
Moderate blue
36.
Seal Brown Supreme House Paint,
S
John W. Masury &
on
37.
Verdi Green #6830 Super House Paint,
Chi-namel Paint and Varnish Co.
38.
Khaki #1 (cotton)
1.2Y
5.5/2.8
Light olive brown
39.
Olive Drab ';52 (wool)
3.OY
3.7/2.8
Moderate olive brown
40.
US Marine Corps Necktie
9.5YR
5.0/2.7
Grayish yellowish
brown
41.
US Marine Corps Overseas Cap (summer)
0.8Y
4.9/3.0
Grayish yellowish
brown
42.
US Marine Corps Pants (summer)
0.6Y
5.2/2.7
Grayish yellowish
brown
43.
US Marine Corps Shirt (summer)
3.OY
5.4/2.8
Light olive brown
44.
ITS Marine Corps Overseas Cap (winter)
0.1GY
2.7/0.8
Olive gray
45.
US Marine Corps Blouse (winter)
1.8CY
2.7/1.0
Olive gray
40.
US Marine Corps Pants (winter)
10.OY
2.9/0.9
Olive gray
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4.3.2 Effects of the Atmosphere and Sun Angle
Two variables that significantly influence the detail and color
fidelity of the imagery are the position of the sun with respect to both
the camera and the target and the optical state or condition of the atmos-
phere when the picture is taken. Understanding these variables is impor-
tant because they are directly related to problems the interpreter may have
with interpreting high-quality, small-scale, color imagery. For example,
an interpreter working on imagery acquired very late in the afternoon must
compensate for the predominately red color of the sunlight reaching the
target. The understanding of the color changes or color shifts caused by
atmospheric and solar effects is important because such knowledge may help
in distinguishing between color changes related to target activity and
color changes related to atmospheric and solar effects. In the following
discussion, atmospheric and solar effects are treated as independent
variables. However, in any given situation, these effects may not be
independent. ATMOSPHERIC TURBULENCE and SCATTERING are the two effects
that ultimately limit the quality of the imagery acquired by camera systems
of excellent overall optical design and performance. This means that
beyond a certain limit, a further increase in the size of the optical
aperture and the focal length of a lens does not produce an increase in the
amount of ground detail that can be resolved. Although a degraded image
results from both atmospheric effects, the physical mechanisms that cause
the image are quite different.
Atmospheric turbulence is caused by random variations of the air
density, i.e., mass per unit volume, caused by random variation in the
temperature and atmospheric pressure along the optical path between the
target and camera. The INDEX OF REFRACTION, being proportional to density
of an optically transparent material like air, is a measure of how much
the direction of a ray of light is deviated on passing through the material.
Collectively, these random variations in the density of the atmosphere,
i.e., index of refraction, cause the atmosphere to appear as through it
were composed of a very large number of transparent glass globes of
different refractive power. These globe-like cells vary from a minimum
size of slightly larger than a golf ball to a maximum size slightly less
than a softball. Because the refractive power and size of these turbu-
lence cells varies randomly, the shape of the wavefront is distorted as it
passes through the turbulent atmosphere on its way from the target to the
camera. Figure 4.4 indicates the image distortion caused by a turbulent
atmosphere. This distortion of the wavefront means that the image of the
target formed by the optical system will be distorted even if the acquisi-
tion system were perfect. Compounding this problem is the variation in
time of the size and refractive power of these turbulence cells. Thus,
during an exposure a "series" of distorted images are recorded on the
film. This distortion of the wavefronts by the atmosphere is more
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Wavefronts
arriving at
camera
0000 c o
'
0 0Oa o
00
Qo0 ~Oaoo ~?,
OpoO~ ~ ~ O
O
Wavefronts of
the light rays
leaving the
target
FIGURE 4.4 IMAGE DISTORTION CAUSED BY A
TURBULENT ATMOSPHERE
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?oo ~So 0 oQ?ov Turbulent
~oooop O be, _ O
` -
c
- -QVV
o O
re
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disruptive to the high spatial frequencies than to the low frequencies.
Consequently, small details in imagery are more easily obscured than large
area targets. Since optical turbulence limits the amount of detail that
can be recorded by a perfect system, photography above approximately 40,000
feet is limited by the atmosphere to a ground resolution of between 2 and 8
inches. Below 40,000 feet, the maximum ground resolution is determined by
a combination of the optical properties of the camera and the atmosphere.
Further degradation of overall detail rendition and color fidelity
of color imagery is caused by matter (both gaseous and particulate) in the
atmosphere. Light that is traveling from the target to the camera is
scattered and absorbed. The absorption or attenuation is caused by
the dissipation of some of the light rays' energy. Optical scattering is
the absorption and re-emission of light by the gaseous and particulate
matter. The way the two phenomenon affect the light and, thus, the
contrast and color fidelity of color imagery is shown in Figure 4.5.
Optical scattering redistributes part: of the light forming the image so
that the scattered light acts as a veil which reduces the overall contrast
of the scene. Furthermore, scattering reduces the contrast of large and
small targets, equally.
The amounts of both optical, scattering and absorption are related
both to the wavelength of the incident light and to the size and structure
of the gaseous and particulate matter in the atmosphere. If the wavelength
of the incident light is much larger than the effective cross-sectional
diameter of the scattering material, then much more blue light than red
light will be scattered. Scattering increases rapidly as wavelength
decreases. The situation is much more complicated when the wavelength of
the incident light is about the same as the diameter of the scattering
material.
In a clear atmosphere and below 10,000 feet, optical scattering
and absorption causes little degradation of image detail or color fidelity.
The degradation increases from 10,000 to 35,000 feet, but beyond that
height, no further increase in image degradation is caused by optical
scattering and absorption. In general, atmospheric scattering gives an
overall blue cast to a properly exposed frame of color imagery.
Another acquisition variable that contributes to the overall
color fidelity of aerial color imagery is the position of the sun with
respect to the position of the camera and target. The terms SUN ANGLE
or SOLAR ALTITUDE, which are diagrammatically defined in Figure 4.6,
define the position of the sun with respect to the camera and the target.
The amount of light illuminating the target varies with the sun angle.
The relationship between sun angle and target illuminance is.shown in
Figure 4.7.
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FIGURE 4.5. LIGHT LOSSES CAUSED BY BOTH ABSORPTION AND SCATTERING
IN THE ATMOSPHERE
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FIGURE 4.6 DIAGRAM OF THE SUN ANGLE OR SOLAR ALTITUDE AND THE RELATIVE
POSITIONS OF THE EARTH, CAMERA PLATFORM, AND THE SUN
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0 30
Sun Angle, degrees
FIGURE 4.7 VARIATION OF TARGET ILLUMINANCE AS A FUNCTION
OF SUN ANGLE
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Color imagery should not be acquired at sun angles of less than
15 to.20 degrees because there is an insufficient amount of light for a
reasonably short exposure time. Also, when the sun angle is low, i.e.,
less than 15 to 20 degrees, the sunlight illuminating the target has a
predominately reddish cast, because most of the blue light has been
scattered before it reaches the target. Because the concentration and
characteristics of the dyes in the color film are selected to achieve a
natural color rendition they are balanced for white sunlight; any color
imagery acquired at these low sun angles would have an overall reddish
cast.
In general the optical systems used are highly corrected for
aberrations and produce a minimum amount of image-quality degradation.
The resolution of a DIFFRACTION LIMITED optical system is as high as can
be achieved without increasing the optical aperture or using shorter wave-
lengths. To achieve this near-diffraction-limited performance the
"optical defects" or aberrations in these optical systems are minimized by
properly balancing the aberrations against each other over a wide range of
wavelengths or different colors.
Platform motion and camera vibration degrade the quality of
aerial imagery by decreasing the resolution and the overall sharpness of
the imagery. However, no information is available to indicate that
platform motion and camera vibration would degrade color imagery any more
than it degrades black-and-white imagery of comparable film-resolution
capabilities.
4.4 EFFECTS OF FILM AND PROCESSING PARAMETERS ON COLOR
AERIAL PHOTOGRAPHY AND COLOR PERCEPTION
4.4.1 Effects of Granularity
The granular structure of the images formed in a dye-based
photographic process is quite different from the granular structure of
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the images formed in a conventional black-and-white silver halide photo-
graphic process. The grains in a conventional black-and-white image are
very small opaque particles of metallic silver. Colored images are formed
by chemically removing, i.e., bleaching, these small metal particles and
then using the remaining reaction products to form cyan, magenta, and yellow
dyes upon subsequent chemical processing. Thus, each of the small, opaque,
silver grains is replaced by one or more translucent blobs of dye of
indeterminant size and shape. The OPTICAL DENSITY of these concentrations
of dye may increase from approximately zero at their edge to 0.75 at their
.center. Both the shape of the optical-density profile for these dye con-
centrations and the optical densities of the images they form are quite
sensitive to the hue or wavelength of light used in a densitometer. On the
other hand, the optical density of an image formed by particles of metallic
silver is nearly independent of color. Not only is the color, shape, size,
and texture of the grains that composed the dye-formed colored image
different, but they are contained in three separate layers of emulsion
rather than in a single layer as in black-and-white silver halide photo-
graphic film.
The VISUAL or LUMINOUS DENSITY of these dye masses appears to be
the major factor in determining the GRAININESS of dye-formed images;
however, this conclusion is based on neither a consensus nor on conclusive
experimental evidence. Nevertheless, when uniformly exposed-and-processed
yellow, cyan, and magenta images are viewed under identical conditions,
the graininess of the yellow image is considerably less than the graininess
of the magenta image, and the graininess of the cyan image is somewhere
between these two. If the GRANULARITY of these images were measured with
a scanning microdensitometer equipped with the proper filters, the
differences between the measured values for the granularities of the
various images would not be as great as one would be led to believe by
the visual appearance. However, the visual or luminous densities of the
dye images can quite possibly account for the marked difference in the
graininess of these images. The effect of this difference between the
granularity or the graininess of dye-formed images on the interpretation
of high-resolution color photography is not known.
The colorimetric properties of color aerial films such as SO-242,
SO-255, and SO-360 are known to vary from roll to roll and from coating to
coating. Although such variations in the colorimetric properties of these
materials can be expected, these variations may not be visually apparent.
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4.4.3 Effects of Processing Variance
Processing color films is a very complicated and difficult task.
Many film factors are controlled during processing, including color balance
and dye density. Any variation from prescribed procedures will affect
these factors.
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Anson, A., "Status of Aerial Color Photography in Government
Agencies", U. S. Army Engineer Topographic Laboratories, Technical
Briefing Report No. 1 (1968), AD 674 189.
Avery, T. E., Interpretation of Aerial Photographs, 2nd ed.,
Burger Publishing Company, Minneapolis, Minnesota (1968).
Bogachkow, N. I., "The Effect of Haze on Aerial Color Photography",
Zhurnal Nauchnoy i Pirklechnoy Fotografii i Kinematografii, 7(2),
pp.112-120 (1962), AD 425 405.
Born, M. and Wolf, E., Principles of Optics, 3rd ed., Pergamon
Press, Oxford (1965).
Chernov, L. A., Wave Propagation in a Random Medium, Dover Publi-
cation, New York (1967).
Colwell, R. N., "Some Practical Applications of Multiband Spectral
Reconnaissance", American Scientist, 49(1), pp. 9-36 (1963).
Dukin, D. R., Bartky, C. D., McManigal, P. G., and Piper, D. G.,
"Aerial Photographic Energy Model", Air Force Avionics Laboratory,
Final Report-68-136 (1968).
Duntley, S. Q., et al., "Visibility", Applied Optics, 3(5),
pp. 549-598 (1964).
Egan, W. G., "Practical Calibration and Control Techniques for
Type 8443 and Ektachrome Films", Grumman Research Department
Memorandum, RM-443J (1969), AD 852 804.
Erb, K. R., Zimmerman, R. R., and Scanlon, T. M., "Atmospheric
Effects of Color Aerial Photography", Air Force Avionics Laboratory,
Final Report-69-280 (1969), AD 859 961.
Farrow, J. B., and Gibson, A. F., "Influence of the Atmosphere on
Optical Systems", Optica Acta, 17(5), pp. 317-386 (1970).
Forst, D. J., Hughes, J. B., Pittman, G. A., and Wallace, R. L.,
"Color Tone Reproduction - Practice Manual", Air Force Avionics
Laboratory, Final Report-67-164 (1969), AD 848 115.
Fried, P. L., "Limiting Resolution Looking Down Through the
Atmosphere", Journal of the Optical Society of America, 56(10),
pp. 1380-1384 (1966).
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Hendeberg, L. 0. and Welander, E., "Experimental Transfer Character-
istics of Image Motion and Air Conditions in Aerial Photography",
Applied Optics, 3(4), pp. 379-386 (1963).
Hufnagel, R. E. and Stanley, N. R., "Modulation Transfer Function
Associated With Image Transmissions Through Turbulent Media",
Journal of the Optical Society of America, 54(1), pp. 52-61 (1964).
Hughes, J. G, Jourdjian, A., Forst, D., Bourque, P., and
LoVetere, K., "Color Tone Reproduction - Theory Manual", Air Force
Avionics Laboratory, Technical Report-67-164 (1968), AD 829 679.
Jensen, N., Optical and Photographic Reconnaissance System,
John Wiley and Sons, New York (1968).
Judd, D. B., MacAdam, D. L., Wyszecki, G., "Spectral Distribution
of Typical Daylight as a Function of Correlated Color Temperature",
Journal of the Optical Society of America, 54(8), pp.1031-1041
(1964).
Keegan, H. J., Schleter, J. C., Baas, G. M., and Hall, W. A., Jr.,
"Spectrophotometric and Colorimetric Study of Color Transparencies
of Some Natural Objects", U. S. National Bureau of Standards,
Technical Report 4794 (1957), AD 132 065.
Keegan, H. J., Schleter, J. C., Haas, G. M., and Hall, W. A., Jr.,
"Spectrometric and Colorimetric Study of Color Transparencies of
Some Man-Made Objects", U. S. National Bureau of Standards,
Technical Report 4953 (1957), AD 156 751.
Lohse, K. H., "Investigation of Multiband Photographic Techniques -
Volume 1", U. S. Army Corps of Engineers, Final Report,
DA-44-009-AMC-1218CD (1965), AD 479 300.
MacAdam, D. L., "Small-Field Chromaticity Discrimination", Journal
of the Optical Society of America, 49(12), pp. 1143-1146 (1959).
Mazurowski, M. J. and Sink, D. R,, "Attenuation of Photographic
Contrast by the Atmosphere", Journal of the Optical Society of
America, 55(1), pp. 26-30 (1965).
Meier, H. K., "Color-Correct Aerial Photography", translated from
Bildnessung and Luftbildwesen (5), pp. 206-214 (1967).
Molineaux, C. E., "Multiband Spectral System for Reconnaissance",
Photogrammetric Engineering, 3(1), pp. 131-143 (1965).
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Myzsko, R., "Effect of Vibration on the Photographic Image",
Journal of the Optical Society of America, 53(8), pp. 935-940
(1963).
Paris, D. P., "Influence of Image Motion on the Resolution of a
Photographic System", Photographic Science and Engineering, 6(1),
pp. 55-59 (1962).
Rao, C.R.N., "Colorimetric Description of Radiation Emerging From
the Top of a Rayleigh Atmosphere", Air Force Cambridge Research
Laboratories, Final Report-68-0090 (1968), AD 672 308.
Reed, H. B., Stiller, J., and Erb, K., "Aerial Color Photographic
Research and Flight Tests", Air Force Avionics Laboratory, Final
Report-68-187 (1968), AD 843 917.
Reed, H. B., "Spectral Filtration Research", Air Force Avionics
Laboratory, Final Report-67-272 (1967), AD 826 978.
Rosenau, M. D., "Image Motion Transfer Functions", Photographic
Science and Engineering, 9(4), pp. 252-255 (1965).
Shack, R. V., "The Influence of Image Motion and Shutter Operation
on the Photographic Transfer Functions", Applied Optics, 3(10),
pp. 1171-1181 (1964).
Smith, J. T., Manual of Color Aerial Photography, 1st ed., American
Society of Photogrammetry, Falls Church, Virginia (1968).
Specht, M. R., Fritz, M. L., and Soren, A. L., "The Change of
Aerial Camera Exposure With Solar Altitude", Photographic Science
and Engineering, 10(3), pp. 150-155 (1966).
Stultz, K. F. and Kock, D. A., "Role of Chromaticity Difference in
Color Graininess Judgments", Journal of the Optical Society of
America, 46(10), pp. 832-837 (1956).
Tatarski, V. I., Wave Propagation in a Turbulent Medium, Dover
Publication, New York (1967).
Winterberg, R. P. and Wulfeck, J. W., "Additive Color Photography
and Projection for Military Photo Interpretation", Photogrammetric
Engineering, 27(2), pp. 450-459 (1961).
Yates, H. W., "A General Discussion of Remote Sensing of the
Atmosphere", Applied Optics, 9(9), pp. 1971-1975 (1970).
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Yereance, R. A., Easterday, J. L., and Stephan, J. G., "Aerial
Photography-Photosensors", Unpublished Battelle Report, October,
1967.
Yost, E. F. and Wenderoth, S., "Multispectral Color Aerial
Photography", Photogrammetric Engineering, 33(9), pp. 1020-1033
(1967).
Yost, E. F. and Wenderoth, S., "Additive Color Aerial Photography",
in Manual of Color Aerial Photography, American Society of
Photogrammetry, Falls Church, Virginia, pp. 541-471 (1968).
Zwick, D., "Colour Granularity and Graininess", Journal of Photo-
graphic Science, 11(5), pp. 269-275 (1963).
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5.0 APPLIED ASPECTS OF COLOR AND COLOR
PERCEPTION IN IMAGE INTERPRETATION
The literature was surveyed to determine the research findings
and experiences of investigators with the interpretation and use of color
aerial photography; included were books, journals, trade journals, and
Government reports. These sources covered many fields of endeavor, _
including military image interpretation, agriculture, archeology, biology,
forestry, geology, geography, hydrology, highway research, mapping, marine
studies, and oceanology. The information sought from these sources
included the advantages and disadvantages of color films; the detection,
identification, and interpretaiton of targets on color films; the optimum
film/filter for particular classes of targets; the use of PI equipment
(stereoscope, magnifier, rear projection, mensuration equipment, etc.)
with color films; and the optimal illumination requirements.
The results of the literature search are discussed below.* Most
findings and experiences reported are opinions and judgments rather than
conclusions drawn from experimental data. In addition, the majority of the
studies used low-altitude, large-scale imagery. Further, the vast: majority
of findings were drawn from studies in areas other than military
interpretation, since the use of color films has been limited in tactical
and strategic interpretation.
The interpretation of color films includes the detection,
identification, and analysis of targets and their backgrounds. Numerous
studies have investigated the use of color films for the interpretation of
many different types of targets and backgrounds. A few of these studies
were experimental and, thus, the findings were conclusions drawn from
experimental data. The majority of studies were operational, and the
findings were based on expert judgment of what was shown and seen on the
imagery.
Since these two types of studies resulted in somewhat different
conclusions, their findings are discussed in two separate sections (5.1.2
and 5.1.4). Many investigators have discussed the theoretical advantages
* The classified information in this topic area is included in the report
entitled "A Review of Color Science and Color Aerial Reconnaissance:
An Addendum".
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of using color films and these discussions are presented first. Another
section discusses the advantages and disadvantages of specific color films
and color techniques as found by users (5.1.3).
5.1.1 Theoretical Advantages of Color Films
Theoretically color films should be superior to panchromatic for
intelligence extraction given comparable resolutions. It is important to
understand the reasons for this theoretical superiority, because these
reasons may help explain the operational success of color films.
(1) The human visual system can differentiate more
color differences than gray-scale differences,
thus on color films (natural or false) greater
detail should be detected (See 2.2.2 Spectral
Range).
(2) If a target's color or false-color is its only
identification clue, then the target can be
identified only on color films.
(3) If a target and its background image are the same
shade (or near shade) of gray on black-and-white
films, but image in different colors on color
films, then the target can best be detected and
identified on color films.
(4) Differences between colors are more discernible
or conspicuous than gray-scale (achromatic)
differences; consequently, a target whose color
differs from its background should be detected
and identified faster on color films.
(5) If a target's spectral distribution is different
from its background, then a film/filter
combination (color, false color, or panchromatic
films with appropriate filters) can be found which
will improve the target" s contrast with its
background. This consideration is the basis for
spectrazonal or multispectral photography (see
4.2.3 Spectrazonal or Multispectral Film and
Techniques) and the use of enhancement filters
(see 5.4 Enhancing the Interpretation of Color
Films).
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5.1.2 Experimental Comparisons of Color Films
With Black and White Films
Several studies have experimentally investigated the inter-
pretation of color films (natural and false) and black and white films.
These investigations compared natural color and/or color infrared (IR)
with black and white imagery of the same scene (at the same scale) using
interpreter performance measures, e.g., detection completeness and
accuracy, identification completeness and accuracy, and time measures.
In general, the targets (tactical, strategic, and COIN) chosen for
interpretation were those found on the available imagery, and those targets
imaged on color films were also imaged on black and white films.
Experimental evidence has not conclusively shown that more targets
can be detected or identified on color or false color films, than on
panchromatic film (Foley and Smith, 1967; MacLeod et al., 1969; Anson,
1966a, 1966b; 1969; Self and Myers, 1970; Levine, 1969). In some
experiments, the interpreters detected and identified significantly
(statistically) more targets on color and color infrared than on black and
white film, but in other experiments, interpreter performance was not
significantly different from film to film. It is very difficult to explain
precisely why this inconsistency has occurred. It is most likely due to
differences between experiments, i.e., different imagery, instructions,
interpreters, tasks, time allotments, targets, etc. However, due to the
complexity and interactions of the differences, it is doubtful that a
satisfactory explanation is possible.
There is evidence that target detection and identification time
is significantly faster on natural color and color infrared films than on
panchromatic (Foley and Smith, 1967; Anson, 1970; Welch R., 1969; NRTSC,
1970; Hostrop and Kawaguchi, 1971).
The use of all three individual spectrazonal (see 4.2.3
Spectrazonal or Multispectral Films and Techniques) transparencies (each
filtered by a red, blue, or green filter on panchromatic) improved detection
and identification performance over that for full-color or black and white
displays generated from the same three filtered transparencies (W:Lnterberg
and Wulfeck, 1961).
5.1.3 Operational Findings on Color Film
and Color-Imaging Techniques
Those investigators who have worked with color films and color
imaging techniques (see 4.2 Photographic Properties of Selected Aerial
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Films, for technical descriptions) have reported advantages and disadvantages
with these, irrespective of target type. The advantages and disadvantages
are listed below by film and/or technique. It should be noted that these
findings are judgments and opinions of users and not conclusions drawn from
experimental data.
5.1.3.1 Natural Color Films (see 4.2.1 Color Films)
5.1.3.1.1 Advantages
(1) Natural color films often permit better identification
of the surface (target or background) details
(Letourneaux, 1969; Parry et al., 1969a; Welch,
1967) if the details are of different colors.
(2) Although natural color films have poorer resolution
than panchromatic films, investigators have reported
subjective impressions of better resolution on color
films due to the greater amounts of target or surface
detail. However, it is not known if this subjective
impression has any relationship to performance.
(3) Targets with distinctive colors greatly different
from their background may be identifiable even though
the targets are beneath the actual resolution of the
color film (Yereance, et al., 1967). Here, target
shape is not resolved, but a distinctively colored
area reveals the target.
(4) Target and ground details in shadows are best
detected and identified on natural color films
(McDaniel and Arntz, 1959; Reed, 1967; Welch, 1967).
Shadow detail reflects skylight which is predominantly
blue. Thus, a film sensitive to the blue region is
necessary for shadow detail. Although panchromatic
films are sensitive in the blue regions, minus-blue
haze filters are often used, thus reducing shadow
detail. A similar result will occur if minus-blue
filters are used with color films. In addition, if
a color film has inherently poor blue sensitivity,
the shadow detail may not be as detectable as on
other color films.
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5.1.3.1.2 Disadvantages
(1) The primary limitation of color films is its lower
resolution compared to black and white. In
intelligence extraction from film, resolution is the
most important film parameter for the identification
and description of targets of concern.
(2) The second primary limitation of natural color film
is its degradation by atmospheric attenuation (see
4.3.2 Effects of Atmosphere and Sun Angle). The
result of this degradation is an overall bluish
cast on the imagery and a reduced color fidelity.
High-altitude and satellite imagery over humid
regions are particularly vulnerable to atmospheric
attenuation, but the problem is reduced when
acquisition is over arid regions (Blackband, 1968;
Anson, 1968b). It has been reported that below
12,000 feet, haze is not a significant problem
(Mott, 1966). However, degradation is dependent
on the amount of particles in the air (this can vary
at any altitude).
Although haze filters (Wratten Filters,
Nos. HF-1 to HF-5 are generally recommended, NRTSC,
1970; or the filter may be an integral layer in the
emulsion) are available to reduce haze degradation,
the blue sensitivity of the film is reduced
(reducing shadow detail and the imaging of blue
colors), and a yellowish cast over the image that can
occur may hinder interpreter performance.
(3) The small exposure latitude of color films also
has implications for interpretation. Many
investigators have reported degraded imagery due to
improper exposure. Generally an overexposure of
one stop can cause a greenish cast on the imagery.
(4) The colors on successive overlapping (stereo) frames
change due to a change in acquisition angle or
VIGNETTING. For example, a blue-green truck on
one frame may be blue on the next frame.
(5) Highly reflective surfaces tend to bloom on color
films and reduce surface detail.
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(6) As acquisition altitude increases, surface colors
tend to blend such that a grouping of targets
(e.g., trees) may have a color that is different
from individual targets (Carneggie, 1968a).
(7) The processing of color films requires more
precision than black and white films. Any deviation
from prescribed procedures can significantly affect
the color fidelity, color balance, and color
contrasts on the image, and thereby affecting
interpretation.
(8) The reproduction of color transparencies for reports,
transparent copies, etc., is difficult and costly.
The most successful reproduction technique (in terms
of color fidelity, balance and contrast) is through
the use of COLOR SEPARATION NEGATIVES where the
film is copied onto three transparent negatives,
through three different: filters; red, blue, and
green. These negatives are then copied, in
register, onto color photographic paper or film.
This technique is time consuming and costly; but
alternative techniques result in copies of reduced
color fidelity and balance.
5.1.3.2 Color Infrared Film (Ektachrome Infrared
8443, See 4.2.2 False-Color Films)
5.1.3.2.1 Advantages
(1) Color IR penetrates haze and smoke better than any
other acquisition materials, because it is used
with a minus-blue filter (Ciesla et al., 1967;
Chaves and Schuster, 1968; Specht, 1970; Anderson,
1969; Pease and Bowden). Many have reported that
it should be preferred to natural color films
for high-altitude photography (TARC, 1965; Reed,
1967).
(2) Color IR images healthy and near-healthy
vegetation as a deep-red or magenta color (Marechal,
1966; Fritz, 1967). Thus, vegetation can be
differentiated from most all other targets and
backgrounds.
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5.1.3.2.2 Disadvantages
(1) The false colors require interpreters to learn a
new set of color/object associations (Leibowitz,
1967).
(2) The range of color produced on Color IR is limited
compared to that for natural color, thus, less
surface detail is imaged (Chaves and Schuster,
1968).
(3) Cloud shadows are very dark because the clouds
filter out infrared radiation (Chaves and
Schuster, 1968).
(4) Details within shadows are illuminated mostly by
blue scattered light from the sky. Hence, the
shadow details are less than on natural color,
because of the film's reduced blue sensitivity and
the use of a Wratten 12 (minus-blue) filter (Chaves
and Schuster, 1968; Reed, 1967; Fritz, 1967;
NRTSC, 1970).
(5) Hardcopy prints of color IR reduce the number of
red and magenta tones and; thus, information may
be lost (Marechal, 1966).
(6) Color balancing during processing is more difficult
than with natural color, because there are no true
colors with which to judge (Reed, 1967; Fritz,
1967).
(7) Exposure latitude is small (normally within 1/2
stop of the correct setting, Fritz, 1967; Welch,
1967).
5.1.3.3 Additive Color Separation (See 4.2.4
Additive Color Separations)
5.1.3.3.1 Advantages
(1) Because the separate transparencies are produced
using panchromatic film, the exposure latitude,
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resolution, and film speed are better than on
color film. Thus, the. advantages of color can
be obtained along with. the advantages of
panchromatic film (Win.terberg and Wulfeck,
1961; Reed, 1967; Welch, 1967).
(2) The intensity and filtering of the light transmitted
through each transparency can be controlled, thus
providing flexibility and control over color
contrasts and colors (Winterberg and Wulfeck, 1961;
Yost and Wenderoth, 1967). This control enables
making of colors that closely match true ground
colors (Yost and Wenderoth, 1971).
(3) Two-color (bi-color) renditions can be displayed;
this may enhance the contrasts of some targets with
their backgrounds (Win.terberg and Wulfeck, 1969;
Yost and Wenderoth, 1967).
(1) The primary disadvantages of separate transparencies
is that during acquisition the scene must be imaged
the same on each transparency (Winterberg and Wulfeck,
1961; Reed, 1967). If differences occur between the
transparencies, they cannot be accurately registered,
and the overall composite may become very poor to
useless. Also, during display, nonregistration may
result in edges showing a "rainbow effect", i.e.,
there will be red, blue, and green fringes along each
edge. This edge degradation may also interfere with
interpretation.
(2) Special equipment is required to display the trans-
parencies for full or partial color.
(3) Processing for each film must be adjusted to
compensate for differences in contrast (Reed, 1967).
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5.1.3.4 Spectrazonal or Multispectral Techniques
(See 4.2.3 Spectrazonal or Multispectral
Film and Techniques)
5.1.3.4.1 Advantages
(1) If exact SPECTROPHOTOMETRIC data are available
for a specific search problem, then a single
film/filter condition should produce optimal
results (Winterberg and Wulfeck, 1961;
Molineaux, 1965).
(2) The film generally used is panchromatic which
has excellent exposure latitude, film speed,
and resolution.
5.1.3.4.2 Disadvantages
(1)
The amount of spectral information for most
tactical, COIN, strategic, cultural and natural
targets and backgrounds is very limited (Winterberg
and Wulfeck, 1961; Yost and Wenderoth, 1971).
(2) For full-scene interpretation, a large number of
film/filter combinations would be required,
since each target/background may require a different
film/filter combination for optimal results
(Winterberg and Wulfeck, 1961).
(3) The spectral distribution of a target may change
when viewed from a different angle, illumination
condition, or altitude (Winterberg and Wulfeck,
1961). Thus, unless acquisition conditions are
known, choosing optimal film/filter combinations
for a target is difficult.
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5.1.3.5 Black and White Infrared (Kodak
Infrared Aerographic Film, free
4.2.4 False-Color Films)
5.1.3.5.1 Advantages
No interpretation advantages over color infrared films (Marechal,
1966) are apparent. However, processing, reproducing, and hard-copy
printing are easier and less costly.
5.1.3.5.2 Disadvantages
Resolution is poor, particularly when lenses used are not
designed to be used with black and white infrared (Marechal, 1966).
5.1.4 Operational Findings on the Interpretation
of Targets and Backgrounds on Color Films
Investigators who have used color films for specific tasks or
targets, generally judge them to be superior to panchromatic films. This
superiority appears to stem from (1) color contrasts, (2) greater surface
details (due to color differences) apparent on color film, and (3) the use
of color as an identification clue. Primarily, however, it appears that
color contrast is the prime factor in the judgments of the investigators.
Consequently, in the following discussion (unless otherwise noted) statements
such as "target A is best detected on film B" mean that the contrast of
target A with its background is highest on film B.
This discussion is divided into three target classes (tactical,
strategic, and cultural) and four backgrounds (vegetation, soils, water,
and geologic features). Available information on the use of color films
for the target types is very limited at this time, since the organizations
interested in these types of targets have not used color extensively. On
the other hand, there is a significant amount of information on the
backgrounds, since color films are used more extensively in agriculture,
forestry, geology, oceanology, etc.
Note that the backgrounds discussed are important in reconnaissance.
It is important to understand how backgrounds appear on color films so
that targets can be distinguished from them. Also, it is important to be
able to identify the type of background present. For example, swamps appear
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as forests on panchromatic, but as swamps on Color IR. Most important,
however, the interpreter should know how to use backgrounds on color films
as clues to intelligence, such as activities, bomb damage, and capability
(crops, minerals, etc.). The purpose of this section is not to inform
interpreters of all the ways the information included can be used in
interpretation, but rather to simply provide what information is available.
5.1.4.1 Tactical Targets
(1) Tactical vehicles within or on vegetation may be
best detected and identified on Color IR. On
Color IR, olive-drab vehicles appear violet,
dark-brown vehicles appear dark-green, and red
vehicles appear yellow (Marechal, 1966). These
false colors have high contrast with surrounding
vegetation which appears as tones of red and
magenta. On natural color films the green, brown,
and blue-green vehicles do not have high contrast
and can blend with the green vegetation.
(2) Camouflaging material, e.g., cut vegetation, green
paint, etc., is best detected and identified on
Color IR. The dead or drying vegetation appears
yellow to brown, and the surrounding live vegetation,
being red or magenta, provides good color contrast.
Green paint for camouflaging generally images
violet on Color IR. Thus, dead vegetation can be
distinguished from green paint, and both, from live
vegetation. On natural color films, camouflaging
may not be detectable because colors are chosen
to blend with the background.
(3) Boats partially hidden by shore canopy are best
detected and identified on Color IR (Foley and
Smith, 1967). Boats generally show as bluish-gray
and provide high contrast against the red and
magenta vegetation. On natural color films their
colors often blend with the water, because of their
similar colors. However, partially submerged boats
(submarines) are best detected on natural color,
because of its excellent water penetrability (see
5.1.4.6 Water).
(4) Trails, fresh vehicular tracks, fresh emplacements,
and other activity that disturbes the soil are best
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detected and identified on natural color
films (McDaniel and Arntz, 1959; Yereance, et al.,
1967; Fischer, 1962). These targets are
primarily disturbed earth where subsurface soils
are visible or shadows are cast. Subsurface
soil may be a different color because of its
type or dampness.
(5) The age, condition, and operability of military
equipment may be better identified on color
films, e.g., from rust spots, paint chips, and
scarring, (NRTSC, 1970).
(6) Color coding (for identification purposes) of
various military equipment, i.e., missiles, rail
equipment, and shipping crates, is best detected
and identified on natural color films.
(7) Disruptive camouflage on airport runways and
taxiways are more effective on natural-color
films because the colors of the camouflage are
designed to confuse the viewer.
5.1.4.2 Strategic Targets
(1) Strategic targets within or on vegetation may be
best detected on Color IR, because the false colors
of the targets contrast sharply with the red or
magenta tones of the vegetation. However, their
large size and often unique shapes and configurations
make them detectable and identifiable on natural
color and panchromatic films.
(2) Industrial or power complexes and mining operations
may be identified by type, products, and processes
used by (a) the color of their waste piles, stock
piles, and products, ground stains, and effluents
(smoke or waste into water), and (b) the effects
of fumes and smoke on the surrounding area
(McDaniel and Arntz, 1959; Yereance, et al., 1967).
For this type of identification, natural color
films would be an aid (there may be other clues
to their identification.
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(3) Road-surface composition is best identified by its
color on natural color films, e.g., dirt or gravel,
asphalt, and concrete (Yereance, et al., 1967).
5.1.4.3 Cultural Objects
(1) Cultural objects within or on vegetation are best
detected and identified on Color IR (Chaves and
Schuster, 1968; Anson, 1970; Anson, 1966) because
their false colors are dissimilar to the red and
magenta tones of the vegetation.
(2) Cultural details, i.e., building types, structural
materials, and the details of tight clusters of
buildings and their condition are best identified
on natural color films (Halliday, 1969;
Letourneaux, 1969; Mintzer, 1968a; Umback, 1968;
NRTSC, 1970).
5.1.4.4 Vegetation Types
(1)
For assessing the vigor of vegetation, Color IR
has been shown to be the best (National Research
Council, 1970; Wert and Roettgering, 1968; Meyer
and Calpouzos, 1968; Norman, 1968; Anson, 1968b;
Colwell, 1968; Wallen and Philpotts, 1971). On
Color IR, healthy vegetation images red and magenta
tones. Unhealthy vegetation (due to nutritional,
disease, nuclear or chemical/biological factors)
images yellow, golden-brown, or silver gray
(Cochrane, 1968; Meyer and Calpouzos, 1968). It
has been reported (Heller, 1968) that as vegetation
progressively dies, its color on natural color
films changes from green to yellow, to brown;
whereas on Color IR, the colors change from magenta
to red, to light pink, to white, to yellow.
(2) The existence of vegetation is best detected on
Color IR (Anson, 1970; Mintzer, 1968a; Welch, 1967).
In areas where vegetation is scant, the sparse color
tone of the vegetation may blend with surrounding
rocks and soils on natural color and black and white
films. However, their existence is immediately
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apparent as tones of red and magenta on Color IR.
Small, low growing shrubs are often misidentified
as rocks or large stories on black and white film;
whereas on Color IR they are readily identified
as vegetation (Chaves and Schuster, 1964; Carneggie,
1968a).
(3) On Color IR, coniferous (pine) trees image magenta,
but deciduous (hardwood) trees image red. This
color difference allows the two classes of trees
to be readily identified (Ciesla, et al., 1967;
Chaves and Schuster, 1968; Eastman Kodak, 1968;
Lauer, 1967; Anson, 1968a). However, the
identification of tree species by their color on
Color IR or natural color films has not been
consistently successful (Parry, et al., 1969b;
Lauer, 1967).
(4) On natural color and Color IR, individual trees are
generally easy to detect and delineate from their
background shadows and surrounding trees and
vegetation; thus, the identification of tree species
by crown shape, texture, and size is enhanced (Anson,
1968b; Haack, 1962).
(5)
For crop identification, the use of natural color
and Color IR films has been the most successful
(Anson, 1970; National Research Council, 1970;
Colwell, 1968; Peastrong, 1968). As seen in
Table 5.1, the use of color for identification of
crops increased identification scores over those for
black and white ("Brightness alone" column). However,
color alone is insufficient for crop identification
(National Research Council, 1970).
(1) Freshly moved earth and disturbed terrain (important
indications of new activity) are best detected and
identified on natural color films, (NRTSC, 1970).
(2) The colors of various soils and sands are a basic
characteristic for the=ir identification, thus
optimal identification would occur with natural color
films (Condit, 1969). But, studies have not
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TABLE 5.1. ACCURACY OF CROP IDENTIFICATION
ON TRUE COLOR FILM (National
Research Council, 1970)
Correct Classification in %
(Sample Sizes in Parentheses) by Using
2. Stereo
4. Color and
1.
Brightness Height
3. Color Stereo Height
Crop Type
Alone
Alone
Alone
Combined
Winter Wheat
5
(78)
6
(54)
17
(78)
49
(35)
Spring Wheat
0
(16)
12
(8)
56
(16)
86
(7)
Spring Barley
6
(16)
45
(11)
56
(16)
71
(7)
Oats
0
(12)
14
(7)
25
(12)
17
(6)
Potatoes
7
(56)
21
(48)
30
(56)
67
(27)
Beets
10
(20)
53
(15)
35
(20)
71
(7)
Corn
20
(5)
40
(5)
40
(5)
100
(4)
Rape
20
(3)
67
(3)
40
(5)
100
(2)
Hop
77
(13)
100
(9)
77
(13)
100
(8)
Tobacco
11
(9)
20
(5)
56
(9)
100
(4)
Hay
11
(54)
69
(67)
9
(54)
29
(34)
Overall Accuracy
11
(284)
38
(232)
29
(284)
57
(141)
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(3)
consistently shown that all soils can be
identified on color films (Parry, et al.,
1969a; Mintzer, 1968). It has, however, been
reported that more soil types can be identified
on color than on panchromatic, with greater speed
and confidence (Parry, et al., 1969a; Chaves and
Schuster, 1968; Anson, 1970).
The differentiation of soil types, in a given
scene, is best detected and identified on
natural color films (Anson, 1969; Mintzer,
1968a; Hostrop and Kawaguchi, 1971).
(4) For predicting slopes in the land, natural color
film (plus the use of a stereoscope) was found
best (Mintzer, 1969; Kuhl, 1970).
(5) For determining drainage patterns and moist
versus dry soils, Color IR was found best (Chaves
and Schuster, 1968; Mintzer, 1969; Mintzer, 1968a;
Peastrong, 1968).
(6) For delineating bare soils from vegetation-covered
soil, Color IR is best (Anson, 1970) since vegetation
images shades of red and soils do not.
(1)
For the detection and identification of the
presence of water or moisture, small streams, and
for delineating the edges of water bodies or moist
soils, Color IR has been found extremely effective
and better than other film types (Witmer, 1968;
Chaves and Schuster, :1968; Anson, 1970; Anson,
1968b; Welch, 1967; Peastrong, 1968; Swanson, 1960;
NRTSC, 1970). On Color IR, the water generally
images dark blue to black, whereas land is red/
magenta from the vegetation, or gray/green from
the soils. These color differences between land
and water provide very sharp contrasts.
(2) For detecting and identifying vegetation floating
on the water or suspended just below the surface,
Color IR has been found most effective (Anderson,
1969; Welch, 1969; Strandberg, 1966).
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(3) For the greatest depth penetration, natural
color films (Schneider, 1968; Helgeson, 1970;
Whitten, 1968; LaViolette and Seim, 1960;
Anson, 1968b) or film/filters maximally sensitive
to the 460 to 500 nanometer region and the 500
to 560 nanometers region of the visual spectrum
are best (Helgeson and Ross, 1970). These films
show subsurface details (down to 200 feet in
imagery of the ocean) such as bottom configurations,
shoals, ridges, deposits, and vegetation (McDaniel
and Arntz, 1969; Anson, 1968a; Swanson, 1960).
Estimates of water depth from its color are not
accurate, although work is continuing on this
aspect (LaViolette and Seim, 1969). In general,
for a particular body of water, the darker the
color the deeper the water.
(4) Natural color films (except where noted) have also
been shown best for the following:
? Locating and tracing water currents (Schneider
and Kolipinski, 1969; LaViolette and Seim, 1969).
? Detecting water pollution and its sources;
identification of pollutants is possible
(Cooper, 1969; Bay, 1968; Strandberg, 1966)
if the pollution has or leaves a unique color
signature such as the yellow-orange stain
from acid mine drainage (Schneider and
Kolipinski, 1969; Bay, 1968; Strandberg, 1966).
?
Detecting phytoplankton distribution and
movement (Schneider and Kolipinski, 1969).
?
Detecting turbidity (Schneider and Kolipinski,
1969; Welch, 1967); if turbidity is
Color IR is best (Anderson, 1969).
due to algae,
?
Detecting fresh water outflows into
(Schneider and Kolipinski, 1969).
seawater
?
Detecting low dissolved oxygen levels is best
on Color IR where water appears milky (Strandberg,
1966).
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5.1.4.7 Geologic Features
DEIITIAL
(1) For identification of rock and mineral types,
natural color film has been found most effective
(Chaves and Schuster, 1964; Chaves and Schuster,
1968; Carter, 1968; Eastman Kodak, 1968; Fischer,
1962; Hostrop and Kawaguchi, 1971). This is due
to the unique colors imaged by various rock and
mineral types which often are indistinguishable
on panchromatic. For example, natural color
shows:
Granite - light-reddish-brown
Rhyolite - greenish-brown
Basalt - black
Limestone - light-brown
Shale - dark-gray to black
Sandstone - yellowish-brown.
(2) Natural color films have also been found best for
detecting and tracing geologic faults and strata
of shale and sandstone (Mott, 1966). Color film
was not found superior to panchromatic film for
limestone strata, however.
(3)
Interruptions in established color sequences
suggest high-angle faulting (Anson, 1968b).
(4) Natural color film has proven superior for land-
form interpretation due to the color contrast of
water, soils, vegetation, and geologic features
(Welch, 1967).
Research had led to the conclusion that, for conventional
mensuration tasks and tolerances, color aerial photography is virtually
equal and indistinguishable from its panchromatic counterpart (Reeves, 1970;
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Harris, et al., 1968; Schallock, 1968; Woodrow, 1967). Conventional color
films have been shown to be vertically stable, and for conventional
tolerances, as accurate as panchromatic for evaluation measurement. (Umback,
1968; Reeves, 1969; Harris, et al., 1968). It should be remembered,
however, that color films have more than one layer and determining an edge
may be more difficult. Thus, when using color films less mensuration
accuracy and greater variability between photogrammetrists would be
expected. The inaccuracies and variability may not be important unless
very close tolerances are required and image scale is extremely small.
5.3 INTERPRETATION TECHNIQUES AND COLOR FILMS
5.3.1 Stereoscopic Viewing
The advantages of using a stereoscope with color films is the
same as for use with panchromatic. As summarized below, stereoscopic viewing
may present problems, but their significance is not presently known. (See
also 2.4 DEPTH PERCEPTION AND COLOR.)
The color of a target on one frame of a stereo pair may be
different from its color on the other frame; thus, when the target is fused
with the aid of a stereoscope, its fused color may be different from the
target's color on either frame (or fusion may not occur at all). The color
differences of a target between frames generally occurs when, on at least
one frame, the target falls on the VIGNETTING affected region. Within this
affected region, the color of targets has a lower brightness value
(2-3 Munsell value steps have been reported, Parry, et al., 1969a). A hue
shift toward the blue may also be noted.
Several investigators (Silvestro and Hammill, 1967; MacLeod, et al.,
1969) have placed a color image under the one side of a stereoscope, and
a black and white image of the same scene under the other side, in hopes
that the visual system would fuse the colors of one side and the better
resolution of the other. All combinations of color, Color IR, and black and
white film have been tried, however, interpreter performance was never
improved. In fact, some interpreters were unable to obtain binocular
fusion.
5.3.2 Magnification
Due to the graininess (or "globiness") of conventional color films,
the usable power of magnification is less than with panchromatic.
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Generally, 10 to 15X has been reported to be maximum for good viewing of
conventional color films. Higher magnifications can be used with films
that have a greater resolving power than these conventional color films.
As the magnification is increased, however, the colors on color
films tend to lose saturation and become diffused (Mott, 1966; Welch,
1967). Pastel shades (unsaturated colors) are particularly affected.
This problem would affect color matching, particularly if the target was
being magnified, and the reference color, e.g., a Munsell chip, was not.
Also, it may affect color naming, in that the color under high magnifica-
tion may be named a "lighter" color than is shown on the film.
5.3.3 Scanning Strategies
An interpreter's scanning strategy should not be different for
color films, unless specific colors are being searched for or specific
colors are being ignored. For example, an interpreter may be searching for
color codes on military equipments. In time, the interpreter may
automatically search for particular colors (which may have intelligence
value) just as he searches for shapes, patterns, and textures. It has
been shown that when color, shape, and size are given as identification
clues, color is used predominantly during search (Williams, 1967).
5.3.4 Multisensor Viewing
Certain target-background contrasts are enhanced by natural color
films, still others are enhanced by Color IR, and target detail may best
be registered on panchromatic. The interpretation of all three films (plus
other sensors) for a given scene would improve the probability that all
targets on the image would be detected, identified, and analyzed.
5.3.5 Change Detection
The color change of a target and/or its background can be
important to intelligence and interpretation (NRTSC, 1970). For optimal
detection of color changes, natural color films would be needed, although
Color IR may be required at times, e.g., for a change in vegetation vigor
as a part of bomb, chemical, or biological damage assessment.
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The interpreter, however, must be aware that a color change on
the film may not be due to the target or background. Rather an apparent
color change can also be due to various factors, i.e., sun angle, altitude,
time-of-day, camera lenses, processing parameters, position of the target
on the frame, etc. (see 4.3 EFFECTS OF TARGET AND ACQUISITION PARAMETERS
ON COLOR AERIAL PHOTOGRAPHY AND COLOR PERCEPTION, and 4.4 EFFECTS OF FILM
AND PROCESSING PARAMETERS ON COLOR AERIAL PHOTOGRAPHY AND COLOR PERCEPTION.
5.3.6 Reporting Strategies
The most common strategy for reporting the color names of targets
has been the use of everyday language. The colors reported have been based
on the judgment of the interpreter, e.g., green vegetation, blue water,
etc.. Although this method provides a general impression of the color
(which may be sufficient for most reporting), color terms usage and
perception vary with people.
Munsell chips (see 3.3.1 Munsell Color System) have been used for
reporting the colors of trees (Parry, et al., 1969a) and soils (Parry, et al.,
1969b) on color films. For these targets the Munsell color chip which was
the closest match to the target's predominant color (see Table 5.2) was
reported e.g., 5YR 3/1. This method is preferred when precise color
reporting is required or when a color sample is needed for communication.
When using Munsell chips four very relevant problems were noted
by Parry, et al. The first problem arose when matching the paint chip with
the transparency. The texture difference between the two, initially caused
perceptual confusion, but the authors apparently were able to adapt to this
situation. Second, the source of illumination for the transparency was
different from that of the chips. However, according to the authors who
used this technique, the sources of illumination could be varied in intensity
and position to achieve reliable color matching. The third problem was
how to report the color of a multicolored target. The authors using this
technique solved the problem by reporting the predominant range of colors
and included other frequently occurring colors (see Table 5.2). The fourth
problem resulted when a particular target fell on successive frames
(stereo-pairs). On at least one frame the target would fall near the edge
and be darkened by the VIGNETTING effect. The frame in which the target
fell closest to the center was used for color matching.
A similar method to the Munsell has also been used at the
State of Ohio Aerial Engineering Office. This method Crafttint colored matte
papers (numbering 250) that are used like Munsell chips. These papers are
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TABLE 5.2 SOILS OF THE LAC BEVIN BASIN AND THEIR MUNSELL
VALUES (Parry, et al., 1969a)
Soil Soil
(.roue Series
Gray Brandon
gleiwl
Brown lirrbeoi
,odzolic
Podzol St. Gabriel
Podzol Ivry
Brown Lesage
podcolic
Pod rot I Must
Rolland
organic
Podzol Piedmont
dark gray Brandon
gleinol
fGoind-
Str..Agathe
.Soil T
ype
Organic
Soil Colo
r in Field
Soil co
lors and neutral values
from air photos
---
Nos. of
Total
carbon
'
Iron
Content
Color
Photos
Pan
photos
exposures
acreage
(
ontent,
,
.
USDA
USCS
percent
percent
Air dry
Al field
Predominant color
Other colors
Predominant
Tonal ra
capacity
or range
present
lone
nge
present
Clay
M11
3
24
3.7
5.0
5Y7'2
2.5Y4/2
5B7/0-1:4/0-I
7.5VR6/4:5/4
No
N7-5.5
IOVR4/l
10YR3/ 1
5BG7/0-1:6/0-1
10YR8/0-1 :6/0-1
Silt loam
ML
I
37
3.0
4.1
10YR3/1
5YR2/l
IOYR8/I-4:5/1-4
5YR4/3-6:5/3-O
N7.5
N7.5-3.5
- -
--
-
--
5YR6/I:7/1
Gravelly
SM
8
66
3.2
7.0
IOVR5/4
IOYR3/2
10YR8/0-4:3/0-4
N5
5
N7-3
5
andy loam
.
.
Fine
SM
1
8
3.9
.3.5
10YR6/3
10YR5/3
IOVR6/1-2:4/l-2
IOYR8/0-4:7/0-4
NO
N8-5
loamy sand
IOVR i/t
Sandy loam
SM
3
1I
2.7
3.5
10YR7/3
I0YR4/3
IOVR8/1-4:4/0 4
568/1:4/I
N5.5
N8-3.5
5Y7/3
5V7/3
588/1:7/2
7.5YR6/2-4:5/2-4
-
.SBG6/1 :7/1
IOYR8/1-4:4/I-4
Gravelly
SM
1
10
4.5
7.4
IOYR6/3
,5YR4/4
It1YR8/0--3:4/0 3
7..5YR7/6:6/6 -
- -
- -
andy Ioam
-
-__-
Mnek
Pt
2
8
47.7
1003'2.5
N3
N4-3
andy loam
SM
3.6
5.0
MRS '2
10VR3/2
5YR6/4-6:5/4-6
N6
3
26
2.5Y6/2
10VR4/2
5BG8/I :5/1
588/1:4/1
No
N7-4
Clay
ML
3.7
5.0
5Y6/l
5V5/I
1)304 '0-2:3/0 2
5139/[-2:7/0-2
N4
.fight ""' I ,
Dam
( SM
6.7
4.8
IOYRS.'4
I0YR3/3
7.5YR6/I-3:4/1-3
7.SVR8/l - -
- No
N6-5
4
II
IOVRS'4.
I0VR3/2
tony s:uul)
Data
SM
3..5
5.0
IOVR4/3
10 \'R3 '3
"
?'
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numbered such that reference can be made to the numbers instead of a color
name. However, the papers are limited in colors and shades, and they do
not relate to a logical system of color naming.
5.4 ENHANCING THE INTERPRETATION OF COLOR FILMS
Image enhancement techniques can be used to increase the contrast
of a target with its background, improve the edge definition of the targets,
or separate certain targets from all other.targets on an image. Such
enhancement can improve interpretation. The use of enhancement techniques
for color films have not been used extensively, because the primary effort
has been to obtain good-quality, color images, rather than enhancement
techniques. Thus very few techniques are presented.
5.4.1 Enhancement During Acquisition
5.4.1.1 Haze Filters
These filters (yellow in color, but usually called minus--blue
filters) are used in conventional cameras (not required with color films
whose first emulsion layer acts as a haze filter) to correct for the effect
of atmospheric haze on the color imagery (see 4.3.2 Effects of Atmosphere
and Sun Angle). Haze (smoke, moisture, dust, etc.) tends to scatter the
blue wavelengths more than those for reds and greens. These scattered
wavelengths, mixing with other wavelengths at the image plane, result in an
image of bluish cast. To avoid this situation a minus-blue filter is used
to selectively reduce the intensity of blue wavelengths, color balance is
thereby improved. The primary problem is that the filter also reduces
information in the blue layer of the film. How this reduced information
affects intelligence extraction is not entirely known, although shadow detail
is reduced.
5.4.1.2 Antivignetting Filters
These filters are used (in conventional color systems) to reduce
the variation in illumination at the focal plane (on the film). On color
film, the edges and corners of the frame appears less bright and often bluish.
To correct for this variance in illumination, filters that are darker at the
center than at the edges provide a more uniform field of illumination at the
focal plane. The primary problem with using these filters is the reduced
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amount of illumination at the focal plane. Color film requires high levels
of illumination for proper color balance and fidelity. Any reduction or
filtering of light may degrade image quality.
These filters can be used over the lens to remove unwanted
wavelengths, leaving optimal wavelengths for particular target/background
contrasts. For example, if interest resides only in red objects in a
particular area, a narrow-band, red filter over the lens will allow only
the red targets to be imaged, and the transmissions of other wavelengths
will be reduced. However, interest in targets of a single color is rare.
5.4.2 Enhancement During Processing
Although the following "enhancements" are feasible, their success
in improving interpretation remains to be shown.
5.4.2.1 Color Separation Negatives
During processing, the multilayered color films can be printed into
individual dye layers called Color Separation Negatives. Each single-colored
layer will emphasize particular color contrasts. In addition, a single dye
layer may have better edge definition than the normal multilayer
transparency. This is important for photogrammetrists since they must use
edges for mensuration.
The overall color balance of color film is under control during
processing. A shift in the color balance could improve certain color
contrasts.
5.4.3 Enhancement During Interpretation
The use of colored filters and colored lights by the interpreter to
enhance certain colors while reducing others on color film are possible
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enhancing techniques. Although these techniques have been discussed in the
literature, they have proven neither practical nor helpful in the overall
interpretation of color film.
The use of a colored filter over an image, or preferably between
the image and light table (Judd, 1954) to enhance a particular color while
reducing others, has often been mentioned. This technique, however, reduces
the amount of light transmitted through the image and requires the filter
to be nearly the same color as the color of interest.
The use of these filters may exaggerate small differences in color,
but otherwise are not considered practical (Judd, 1954).
5.4.3.2 Colored Lights
Colored light as a rear illuminant may also be used to enhance
certain colors. Although this technique may exaggerate small differences
in color, it is not considered practical.
5.5 ILLUMINATION CONDITIONS AFFECTING THE
PERCEPTION OF COLOR IMAGERY
The illumination conditions during the interpretation or judging
of color imagery, color prints, color maps, etc., are important. Both the
intensity level of the illuminant and its SPECTRAL DISTRIBUTION directly
affect the perception of colors. For example, if the intensity of the
illumination is too low, then colors will be too dim and detail in the image
will be difficult to detect. If the illuminant's spectral distribution is
not approximately equal in intensity at each wavelength, it will have a
predominant color of its own, and thereby tint the colors it is illuminating.
5.5.1 Illuminant Specifications for Light Tables
5.5.1.1 Intensity
The intensity of the illuminant should be variable from below
75 footlamberts (without visible flicker) to a preferred maximum of
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2500 footlamberts or to, at least, 1500 footlamberts (Boeing, 1969; NRTSC,
1970). For best viewing of color transparencies a level of approximately
900 footlamberts has been recommended with an illuminant COLOR TEMPERATURE
of 5000 K (Bartleson and Witzel, 1967). Ideally, the intensity level should
neither shift during viewing nor vary across the viewing surface.
5.5.1.2 Spectral Distribution
The spectral distribution of the illuminant should have equal
intensity at all visible wavelengths, but minimized below 380 nanometers and
above 750 nanometers (Boeing, 1969; Welch, 1967). For color transparencies
an illuminant with a spectral distribution matching a color temperature of
5000 K has been recommended (Bartleson and Witzel, 1967). Ideally the
spectral distribution should not change during viewing, change when the
intensity is varied, or vary across the viewing surface.
Sorens (1967) states that the color of the rear illuminant is not
critical because the eye adjusts or adapts to the color of the illuminant.
However, for critical color naming, color matching, detecting color
differences, or searching for a particular color, the color of the illuminant
may indeed affect color judgments.
5.5.2 Illuminant Specifications for Ambient Lighting
The intensity of the ambient illuminant should be variable up to
30 to 35 footcandles (Boeing, 1969) with its SPECTRAL DISTRIBUTION near
that of a light source with a COLOR TEMPERATURE of 5000 K.
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Boeing Company, "Human Engineering Design Guide for Image Inter-
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Dalke, G. W., "Multi-Image Correlation Systems for MGI, Phase I",
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Helegson, G. A. and Ross, D. S., "Remote Sensor Imaging for Ocean-
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Lauer, D. T., "The Feasibility of Identifying Forest Species and
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LaViolette, P. E. and Seim, S. E., "Satellites Capable of Ocean-
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Leibowitz, H. W., "The Human Visual System and Image Interpre-
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Letourneaux, P. J., "Improving Quality of Aerial Color Prints",
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Llewellyn, W. E., "Project Compass Haste (Phases I, V. VII)",
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Lohse, K. H., "Investigation of Multiband Photographic Techniques,
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Marechal, A., "Camouflage Detection and Black and White Infrared
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Meyer, M. P. and Calpouzos, L., "Detection of Crop Diseases",
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Meyer, M. P. and French, D. W., "Detection of Diseased Trees",
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Mott, P. G., "Some Aspects of Color Aerial Photography in Practice
and Its Application", The Photogrammetric Record, 5(28),
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Myers, L. B. and Ory, T. R., "The Evaluation of Color Imagery and
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Reeves, F. B., "Mensuration: Color Versus Pan", Photogrammetric
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Stoeckelar, E. G., "Use of Color Aerial Photography for Pavement
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Wert, S. L. and Roettgering, B., "Douglas-Fir Beetle Survey With
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A part of the spectrum (usually infrared, visible, and ultraviolet
wavelengths) that causes chemical changes to take place in light-
sensitive photographic emulsions. The light that creates images on
light-sensitive material. The blue or violet portion of the
spectrum would be the actinic band of light for blue- or violet-
sensitive photographic materials.
The formation of a color by mixing light of two or more other colors.
Most colors may be formed by mixing light of three conveniently
selected primary colors (blue, green, and red) in the proper pro-
portions. Some colors may be formed by mixing light of two colors.
For example, a mixture of blue and green lights produce cyan, a
mixture of blue and red lights produce magenta, and a mixture of
green and red lights produce yellow.
A lens or optics that makes convergent or divergent rays parallel.
A unit used to numerically express the perceptual difference between
two colors.
A measure of the degree to which perceived colors illuminated by a
source compared to the perceived colors when illuminated by a
standard source under specified condition. The index ranges from
0 to 100. An index of 100 means that the source affects the appear-
ance of color the same as the standard. An index of 50 is an example
of the shift from fluorescent light to incandescent light. The basic
problem with this index is understanding what the numbers mean in
terms of perceived colors. For examples, how the colors are per-
ceived when illuminated by a source with an index of 83 is difficult
to determine.
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The temperature (in Kelvin) of a "blackbody" radiator whose
SPECTRAL DISTRIBUTION matches that of the color being designated.
COMPLEMENTARY COLORS (COMPLEMENTS)
Colors that when combined with another color produce a mixture
which color-matches some agreed upon achromatic color. Colors
which appear gray when mixed are called complementary.
A photosensitive material with high resolution, and low scattering
and sensitivity, which is primarily sensitive to the ultraviolet
and blue portions of the spectrum.
A concept that the ultimate limiting factor in the resolving power
of an optical system is determined by the ratio of focal length to
diameter of the aperture.
Traveling in many different directions.
Chemicals that form dyes in the emulsion by reacting with the
oxidized developer products formed during development. The amount
of dye in any one place is proportional to the exposure in that
layer of the color film.
The mealy appearance of the image caused by the clumping together
of the silver grains or, in color transparencies, clumping together
of the globules.
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A term referring to the granular structure of the sensitive emulsion
as represented by the measured variation in the distribution of an
apparently uniform silver- or dye-globule deposit. It is a scien-
tific concept, whereas graininess is a subjective visual impression
created by the granular structure of a photographed material.
A measure of the power of a substance to refract (to bend a ray of
light or change its direction) light. It is the ratio:
sine of incidence angle
sine of refraction angle
when ray is incident from the air side of a glass-air boundary.
The greater the directional change, the higher the refractive
index, e.g., for air the index is 1.00029 and for glass, from 1.5
to 1.8.
A sphere whose inside is coated with highly reflective white
material used to diffuse collected light and thereby reducing
directional effects.
Certain wavelengths produce hues which do not change as far out on
the retina as saturation is elicited. These wavelengths are 464,
489, and 571 nanometers.
The optical density of a medium as it appears visually to the
standard observer. To measure the visual density of a medium a
densitometer is used which duplicates the human photopic curve (y
of the standard observer).
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A yellow filter that will not transmit blue wavelengths, thus
called a minus-blue filter.
NEUTRAL DENSITY FILTER
A filter which absorbs and transmits wavelengths of light equally
and gray in color. These filters can be combined (stacked) to
provide a wide range of densities.
The logarithm of the reciprocal of the transmittance of a medium.
1
D = log10 (TRANSMITTANCE) = log10 (opacity)
A film that is nearly equal in sensitivity to all wavelengths of
the visual spectrum.
Vision as it occurs when the eye is light-adapted and can fully
discriminate all colors.
Vision experienced by the normal eye when adapted to very low levels
of illumination. The maximum of the relative spectral visual
sensitivity is shifted to 510 nm, and the spectrum is seen un-
colored. The rod receptors in the retina are considered to be the
active elements under these conditions.
A silver compound, sensitive to light, and used in film emulsions
to form a latent image.
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The angle measured by the ratio of the surface of the portion of a
sphere enclosed by the conical surface forming the angle, to the
square of the radius of the sphere.
Referring to the measurement of the amount of light at each wave-
length or within narrow bands of wavelengths.
The amounts of a radiant quantity for the various wavelengths of
the spectrum. See Figures 3.5 and 3.6 for examples.
The relative energy (amount of light) emitted from a source at
each wavelength.
In sensitometry, applied to a measurement made by collimated or
essentially parallel light rays;, referring to reflection, or
transmission without scattering or diffusion.
A binocular ability to see depth due to a disparity of the two
retinal images of a scene.
The density of a medium as it appears visually to the standard
observer. To measure the visual. density of a medium a densitometer
is used which duplicates the human photopic curve (y of the standard
observer).
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A gradual reduction in density of parts (generally at the edges and
corners) of a photographic image caused by stopping some of the rays
entering the lens. Thus, a lens mounting may interfere with the
extreme oblique rays.
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The following listing represents suggested reading by selected
topic. Within a topic, references are listed in order of increasing
technical difficulty.
Smith, J. T., Manual of Color Aerial Photography, 1st ed.,
American Society of Photogrammetry, Falls Church, Virginia (1968).
Burnham, R. W., Hanes, R. M., and Bartleson, C. J., Color:
A Guide to Basic Facts and Concepts, John Wiley and Sons, New York,
New York (1963).
Evans, R. M., An Introduction to Color, 1st ed., John Wiley and
Sons, New York (1948).
Billmeyer, F. W., Jr. and Saltzman, M., Principles of Color
Technology, 1st ed., Interscience Publishers, New York (1966).
Evans, R. M., Hanson, W. T., and Brewer, W. L., Principles of
Color Photography, John Wiley and Sons, New York (1953).
Judd, D. B. and Wyszecki, G., Color in Business, Science and
Industry, 2nd ed., John Wiley and Sons, New York (1963).
Committee on Colorimetry - Optical Society of America, The Science
of Color, Thomas Y. Crowell Company, New York (1953).
Wyszecki, G. and Stiles, W. S., Color Science: Concepts and Methods,
Quantitative Data and Formulas, John Wiley and Sons, New York (1967).
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7.2 ANATOMY AND PHYSIOLOGY OF COLOR VISION
Mueller, C. G. and Rudolf, M., Light and Color, Life Sciences
Library, New York (1966).
Burnham, R. W., Hanes, R. M., and Bartleson, C. J., Color: A.
Guide to Basic Facts and Concepts, John Wiley and Sons, New York
New York (1963).
Gregory, R. L., Eye and Brain, World University Library, McGraw-
Hill, New York (1966).
Graham, C. H., Vision and Visual Perception, John Wiley and Sons,
New York, New York (1965).
LeGrande, Y., Light, Color, and Vision, Chapman and Hall Ltd.,
London, England (1968).
Kronfeld, P. C., McHugh, G., and Polyak, S. L., The Human Eye in
Anatomical Transparencies, Baush and Lomb Press, Rochester,
New York (1943).
Southall, J.R.C., Physiological Optics, Dover Publications, Inc.,
New York (1937).
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Mueller, C. G. and Rudolf, M., Light and Color, Life Science
Library, New York (1966).
Burnham, R. W., Hanes, R. M., and Bartleson, C. J., Color: A Guide
to Basic Facts and Concepts, John Wiley and Sons, New York, New York
(1963).
Evans, R. M., An Introduction to Color, 1st ed., John Wiley and
Sons, New York (1948).
Gregory, R. L., Eye and Brain, World University Library, McGraw-
Hill, New York (1966).
Graham, C. H., Vision and Visual Perception, John Wiley and Sons,
New York, New York (1965).
Committee on Colorimetry - Optical Society of America, The Science
of Color, Thomas Y. Crowell Company, New York (1953).
Wysezecki, G., and Stiles, W. S., Color Science: Concepts and Methods,
Methods, Quantitative Data and Formulas, John Wiley and Sons, New York
New York (1967).
LeGrande, Y., Light, Color, and Vision, Chapman and Hall, Ltd.,
London, England (1968).
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Burnham, R. W., Hanes, R. M., and Bartleson, C. J., Color: A
Guide to Basic Facts and Concepts, John Wiley and Sons, New York,
New York (1963).
Lewis, M. F. and Ashby, F. K., "Diagnostic Tests of Color Defect-
ive Vision Annotated Bibliography, 1956-66", AM 67-8, Federal
Aviation Administration, Office of Aviation Medicine, Washington,
D. C. (1967).
Garra, A. A. and Briggs, S. J., Image Interpretation - State
of the Art Review, The Boeing Company, Aerospace Group, Seattle,
Washington (1970).
Lakowski, R., "Psychological Variables in Colour Vision Testing",
Paper #52, read at the First Institute Congress on Colour, June
1969, Stockholm, Sweden, AD 695 343.
Farnsworth, D., The Farnsworth-Munsell 100-Hue Test for the Exami-
nation of Color Discrimination Manual., Munsell Color Company,
Baltimore, Maryland, Rev. Ed. (1957).
Judd, D. B., "Color Blindness and the Detection of Camouflage",
Science, 97, pp. 544-546 (1943).
Judd, D. B., "Facts of Color Blindness", Journal of the Optical
Society of America, 33(6), pp. 294-307 (1943).
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Mueller, C. G. and Rudolf, M., Light and Color, Life Science
Library, New York (1966).
Burnham, R. W., Hanes, R. M., and Bartleson, C. J., Color:
A Guide to Basic Facts and Concepts, John Wiley and Sons, New York
(1963).
Evans, R. M., An Introduction to Color, 1st ed., John Wiley and
Sons, New York (1948).
Billmeyer, F. W., Jr. and Saltzman, M., Principles of Color
Technology, 1st ed., Interscience Publishers, New York (1966).
"Light", Scientific American, 219(3), September (1968).
Judd, D. B. and Wyszecki, G., Color in Business, Science
and Industry, 2nd ed., John Wiley and Sons, New York (1963).
Committee on Colorimetry - Optical Society of America, The
Science of Color, Thomas Y. Crowell Company, New York (1953).
Wyszecki, G. and Stiles, W. S., Color Science: Concepts and
Methods, Quantitative Data and Formulas, John Wiley and Sons,
New York (1967).
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7.6 COLOR SYSTEMS
Smith, J. T., Manual of Color Aerial Photography, 1st ed.,
American Society of Photogrammetry, Falls Church, Virginia (1968).
Burnham, R. W., Hanes, R. M., and Bartleson, C. J., Color:
A Guide to Basic Facts and Concepts, John Wiley and Sons, New York,
New York (1963).
Kelly, K. L., "A Universal Color Language", Color Engineering,
3(2), pp. 16-21 (1965).
Evans, R. M., An Introduction to Color, 1st ed., John Wiley and
Sons, New York (1948).
Billmeyer, F. W., Jr. and Saltzman, M., Principles of Color
Technology, 1st ed., Interscience Publishers, New York (1966).
Newhall, S. M., Nickerson, D., and Judd, D. B., "Final Report of
the O.S.A. Subcommittee on the Spacing of the Munsell Colors",
Journal of the Optical Society of America, 33(7), pp. 385-418
(1943).
Judd, D. B. and Kelly, K. L., The ISCC-NBS Method of Designating
Colors and A Dictionary of Color Names, National Bureau of
Standards Circular 553 (1955).
Richter, M., "The Official German Standard Color Chart", Journal
of the Optical Society of America, 45(3), pp. 223-226 (1955).
Judd, D. B., Chamberlin, G. J., and Haupt, G. W., "Ideal Lovibond
Color System", Journal of the Optical Society of America, 52(7),
pp. 813-819 (1962).
Gourley, J., Rib, H. T., and Miler, R. D., "Automatic Technique
for Abstracting Color Description from Aerial Photography",
Photographic Science and Engineering, 12(1), pp 27-35 (1968).
Committee on Colorimetry - Optical Society of America, The Science
of Color, Thomas Y. Crowell Company, New York (1953).
Wyszecki, G. and Stiles, W. S., Color Science: Concepts and
Methods, Quantitative Data and Formulas, John Wiley and Sons,
New York (1967).
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Billmeyer, F. W., Jr. and Saltzman, M., Principles of Color
Technology, 1st ed., Interscience Publishers, New York (1966).
Billmeyer, F. W., Jr., "Current American Practice in Color Measure-
ment", Applied Optics, 8(4), pp. 737-750 (1969).
Erhart, F. H., ed., Principles of Color Sensitometry, 2nd ed.,
Society of Motion Picture and Television Engineers, New York
(1963).
Onley, J. W., "Analytical Densitometry for Color Print Evaluation",
Journal of the Optical Society of America, 50(2), pp. 177-182
(1960).
Powers, S. A. and Miller, I. E., "Pitfalls of Color Densitometry",
Photographic Science and Engineering, 7(1), pp. 59-67 (1963).
James, T. H., ed., Theory of the Photographic Process, 3rd ed.,
MacMillan Company, New York (1966), "The Sensitometry of Color
Films and Papers" (J. L. Simonds), pp. 450-463.
Wyszecki, G. and Stiles, W. S., Color Science: Concepts and
Methods, Quantitative Data and Formulas, John Wiley and Sons,
New York (1967).
Nimeroff, I., Colorimetry, National Bureau of Standards Monograph
104 (1968).
Nimeroff, I., "Propagation of Errors in Tristimulus Colorimetry",
Journal of the Optical Society of America, 50(2), pp. 177-182
(1960).
Nimeroff, I., "Propagation of Errors in Spectrophotometric Colori-
metry", Journal of the Optical Society of America, 43(6),
pp. 531-533 (1953).
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7.8 COLOR AERIAL RECONNAISSANCE
Smith, J. T., Manual of Color Aerial Photography, 1st ed.,
American Society of Photogrammetry, Falls Church, Virginia (1968).
New Horizons in Color Aerial Photography, American Society of
Photogrammetry, Falls Church, Virginia (1969).
Anson, A., "Status of Aerial Color Photography in Government
Agencies", U. S. Army Engineer Topographic Laboratories, Technical
Brief Report No. 1 (1968), AD 674 189.
Avery, T. E., Interpretation of Aerial Photographs, 2nd ed.,
Burger Publishing Company, Minneapolis, Minnesota (1968).
Llewellyn, W. E., "Project Compass Haste (Phases I, V, VII)",
Wright-Patterson Air Force Base, Final Report, ASD TR-69-101
(1969), AD 504 715L.
Garra, A. A., and Briggs, S. J., "Image Interpretation State-of-
the-Art Review", The Boeing Company, Aerospace Group, Seattle,
Washington (1970).
National Research Council, Remote Sensing With Special Reference
to Agriculture and Forestry, National Academy of Sciences (1970).
Evans, R. M., Hanson, W. T., and Brewer, W. L., Principles of
Color Photography, John Wiley and Sons, New York (1953).
Jensen, N., Optical and Photographic Reconnaissance System,
John Wiley and Sons, New York (1968).
Jones, T. H., ed., Theory of the Photographic Process, 3rd ed.,
MacMillan Company, New York (1966).
Mac Adam, D. L., "Color Science and Color Photography", Physics
Today, 20(1), pp. 27-39 (1967).
Zwick, D., "Colour Granularity and Graininess", Journal of Photo-
graphic Science, 11(5), pp. 269-275 (1963).
Forst, D. J., Hughes, J. G., Pittman, G. A., and Wallace, R. L.,
"Color Tone Reproduction - Practice Manual", Air Force Avionics
Laboratory, Final Report-67-164(1969), AD 848 115.
Forst, D. J., Hughes, J. G., Pittman, G. A., and Wallace, R. L.,
"Color Tone Reproduction - Theory Manual, Air Force Avionics
Laboratory, Final Report-67-164(1968), AD 829 676.
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Page
Absorption, of light 50
Accommodation 4
Acquired color defects 36
Adaptation 24
Additive 54
Additive color separations 103
Additive color separations, advantages 127
Additive color separations, disadvantages 128
Aerial films 100
Aerial perspective 26
After images (positive and negative 19
Analytical densitometry 87
Anatomy of the eye 3
Anomalous trichromats 35
Antivignetting filters 143
Aqueous humor 4
Area effect 16
Arbitrary three-filter densities 86
Atmospheric attenuation 110, 125
Atmospheric turbulence 108
B
Bezold-Brucke effect 10
Binocular cues of depth 26
Black and white infrared 130
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Black and white infrared, advantages
130
Black and white infrared, disadvantages
130
Black content
65
Blind spot
5, 6
Bloom
125
Brightness
9, 17
Burnham-Clark-Munsell color-memory test
39
Campimeter test
40
Camouflage detection film
101, 126
Change detection
140
Choroid
4
Chroma
60
Chromatic aberration
21
Chromatic adaptation
24
Chromastereopsis
28
Chromaticity coordinates
64
CIE
62
CIE color difference unit
77
Ciliary body
4
Collimation optics
75
Color adaptation
24
Color aerial photography
94
Color constancy
20
Color capabilities and skills
29
Color changes due to altitude increases
110
Color and color photography, reproduction
53
Color densitometer
83
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Colormetric densities 86
Color differences and tolerances 81
Color, effect on cues of depth 28
Color fidelity 108
Color fields 13
Color films 99
Color films, advantages 124
Color films, disadvantages 125
Color film and color imagery techniques,
operational findings 124
Color film mensuration 138
Color film processing, tolerance in 116
Color film, theoretical advantage of 122
Color film theory 94
Color zones 13
Colorimeter 75
Colorimeter, Lovibond 65
Colorimeters, visual tristimulus 75
Colorimetric data and error analysis,
treatment of 77
Colorimetry 70
Colorimetry, visual 75
Color infrared film 101, 126
Color infrared film, advantages of 126
Color infrared film, disadvantages of 127
Color matching functions 64
Color, measurement of 70
Colors, metameric 78
Color normals 9
Color perception, effects of age on 36
Color perceptual phenomena 16
Color, physics of 46
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Color, psychophysical aspects of 46
Color rendering 83
Color rendering index 83
Color reversal film 94
Color reproduction, additive method of 54
Color reproduction, subtractive method of 54
Color systems 60
Color versus black and white film,
experimental comparisons of 123
Color vision defects, congenital versus
acquired 36
Color vision defects, types of 35
Color vision tests 37
Complements 19, 96
Cones 6
Congenital color defects 36
Constant hues 10
Convergence 26
Cornea 4
Cyan 54
Dark adaptation 24
Defective color vision 34
Densitometer, color 83
Densitometry, analytical 85
Densitometry, integral 85
Densitometric Munsell 69
Density, specular and diffuse 85
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Density, visual or luminous
86
Depth perception and color
25
Depth, perceptual uses of
25
Deuteranomals
35
Deuteranopes
35
Diagram, CIE
63
Dichromatism
35
Dichromats
35
Diffuse density
85
DIN
67
Dominant wavelength
64
Dunkelstufe
67
Dyes
54
Dye coupler
94
Dye globules, optical density of
115
E
Edge effect
17
Effects of atmosphere and sun angle
108
Effects of lens and lens aberrations
114
Effects of platform and camera vibration
114
Effects of target and acquisition parameters
on color aerial photography and color per-
ception
103
Enhancement of color film during processing
144
Enhancement of color film during acquisition
143
Enhancement during interpretation
143
Electromagnetic waves
46
Equivalent neutral density
86
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Equivalent neutral printing density 88
Eye muscles 3
Eye structure 3
F
False color films 101, 126
Farbton 67
Farnsworth-Munsell 100-Hue Test 38
Field (geometric) of color 13
Films/processing parameters and color film
variance, effects of 116
Filters, antivignetting 143
Fovea centralis 4
Full color content 65
G
Ganglion fiber layer 6
Geologic features 138
Geometric metamerism 81
Granularity 114
Granularity, effects of 114
Ground resolution 108
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11, 12, 13,
29, 53
I
Identification, color 32
Illusions 16
Illuminant, specifications 46, 145
Illuminants 62
Illumination conditions affecting the
perception of color imagery 145
Index of refraction (of air) 108
Infrared, color 101
Instrumental metamerism 81
Integral densitometry 85
Integral printing densities 85
Integral spectral densities 87
Integrating sphere 75
Interposition of colors 25
Interpretation, enhancement during 144
Interpretation techniques and color films 139
Inter-Society Color-Council Color Aptitude
Test (ISCC-CAT) 38
Invariable hues 10, 16
Invariant hues 10
Iris 4
Irradiation 21
ISCC-NBS color system 69
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Latent image
Lateral geniculate body
Lens and lens aberrations
Lens (of the eye)
Light
Light adaptation
Lightness
Light tables, illuminant specification for
Linear perspective
Lovibond
Luminous density
96
9
114
4
46
24
53
145
26
65
86
Mach bands
21
Macular area
4
Maerz and Paul
70
Magenta
54
Magnification, of color film
139
Matching, color
32
Memory, color
30
Mensuration of color films
138'
Metameric pairs
78
Metamerism
78
Metamerism, geometric
81
Metamerism, instrumental
81
Methuin
70
Minus-blue filter
143
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Monochromats 35
Monocular cues of depth 25
Multisensor viewing 140
Multispectral film 102
Multispectral techniques, advantages 129
Multispectral techniques, disadvantages 129
Munsell, densitometric 69
Munsell system 60
N
Naming, color 32
Natural color films 99, 124
Natural color film, advantages of 124
Natural color film, disadvantages of 125
Narrow band (wavelength) filters 144
Nerve pathway from eye to brain 3
Normal color vision 9
NuHue 70
0
Operational findings on interpretation 130
Optic disc 6
Optic nerve 6
Optic radiations 9
Optic tracts 6
Optical scattering 108
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65
125
P
Panchromatic 54
Perceptual phemomena 16
Peripheral retina 6
Peripheral vision, importance of 13
Photographic properties of selected
aerial films 100
Photopic curve 14
Photoreceptors - see rods and cones
Physics of color 46
Physiology of color vision 3
Plochere 70
Primary hues 11, 12
Processing, enhancement of color film
during 144
Processing variance, effects of 116
Protanomals 35
Protanopes 35
Pseudoisochromatic chart tests 37
Pulfrich phenomenon 29
Pupil 4
Purity, CIE 64
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Reflection of light
Reflectance, spectral
Reporting strategies
Resolution, ground
Retina
Reversal development
Ridgeway
Rods and cones
Sattigung
Saturation
Scanning strategies
Scattering
Sclera
Scotopic curve
Sensitivity of the retina
Simultaneous contrast
Soils
Solar altitude
Spectral analytical density
Spectral distribution
Spectral distribution curve
Spectrophotometers
Spectrazonal film
Spectrazonal techniques, advantages
Spectrazonal techniques, disadvantages
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50
50
141
108
3
99
70
6
67
30, 53, 60
140
108
4
14
13
17
134
110
87
46
46
73
102
129
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Spectrazonal transparencies
123
Specular density
85
Spreading effects
21
Standard observer
14,
62
Stereoscopic viewing
139
Stereopsis
25
Subtractive color reproduction
54
Sun angle
110
Superior colliculus
9
Targets, cultural
105,
106,
133
Target detection and identification
123
Targets, strategic (as seen in color)
132
Targets, tactical (as seen in color)
131
Test battery usage, explanation of
40
Tests, color vision
37
Textile Card Association
70
Three-layer emulsion
94
Threshold for detecting color
9
Threshold for identifying color
9
Transmittance, spectral
50
Tripack
94
Tristimulus colorimeter
76
Tristimulus values, CIE
64
Tritanope
36
True color films
99,
124
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Unique hues
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11
V
Value, Munsell 60
Vegetation types 133
Vibration 114
Vignetting 125, 139
Visual colorimetry 75
Visual cortex 9
Visual densities 86
Visual spectrum 14, 46
Visual tristimulus colorimeters 75
Vitreous humor 4
Villalobos 70
W
Water 136
Wavelength 46
Wavelength discrimination 30
White content 65
Yellow dye 54
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