A REVIEW OF COLOR SCIENCE AND COLOR AERIAL RECONNAISSANCE

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04560A007300010030-5
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 186
• Document Creation Date: December 28, 2016
• Document Release Date: March 25, 2003
• Sequence Number: 30
• Publication Date: January 1, 1972
• Content Type: REPORT

Approved For Release 2003/05/14: CIA-RDP78BO456OA00730001003egNFIDENTIAL
TECHNICAL
PUBLICATION
NATIONAL PHOTOGRAPHIC
INTERPRETATION CENTER
A REVIEW OF COLOR SCIENCE AND
COLOR AERIAL RECONNAISSANCE
CONFIDENTIAL
Declass Review by NIMA / DoD
NPIC/R-03/72
JANUARY 1972
GROUP Ii EXCLUDED FROM
AUTOMATIC DOWNGRADING
AND DECLASSIFICATION
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This document contains information affecting
the national defense of the United States,
within the meaning of Title 18, 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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A REVIEW OF COLOR SCIENCE AND
COLOR AERIAL RECONNAISSANCE
January 1972
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1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . .
1
1.1 PURPOSE AND SCOPE . . . . . . . . . . . . . . . . . . . . .
1
1.2 FORMAT . . . . . . . . . . . . . . . . . . . . . . . . . .
2
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 . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
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
2.3.1 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
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)
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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 Colorimetric 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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4.4.1 Effects of Granularity . . . . . . . . . . . . . . . . 114
4.4.2 Effects of Film Variance . . . . . . . . . . . . . . . 115
4.4.3 Effects of Processing Variance . . . . . . . . . . . . 116
5.0 APPLIED ASPECTS OF COLOR AND COLOR PERCEPTION IN IMAGE
INTERPRETATION . . . . . . . . . . . . . . . . . . . . . . . 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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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 3.18
A SCHEMATIC DIAGRAM OF A TRISTIMULUS COLORIMETER . .
76
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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FIGURE 4.7 VARIATION OF TARGET ILLUMINANCE AS A FUNCTION OF
SUN ANGLE . . . . . . . . . . . . . . . . . . . . . .
113
TABLE 2.1 WAVELENGTH REGIONS AND HUE NAMES . . . . . . . . . . .
12
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 5.1 ACCURACY OF CROP IDENTIFICATION ON TRUE COLOR FILM . .
135
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 as ects 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 should be as up-to-date as
possible and based on sound empirical or operationally
proven evidence.
* 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 review 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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Iris 1 \ \ Macular area
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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
light
Direction of
impulses
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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Left Right
ptic nerve
Chiasma
Geniculate body
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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_P4 luo 5Z0 ,:0 600 6i0
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-BRUCKE 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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r
75 650 625 800 57
5 550 525 SOO 475 4!
Wavelength, nanometers
FIGURE 2.5 BEZOLD-BRUCKE PHENOMENON.
2.2.2 Spectral Range
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 (1971)*, for
example, notes that the blue primary is between 470 and 480 nanometers;
personal conversation
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