A RECOMMENDED COLOR VOCABULARY FOR COLOR AERIAL RECONNAISSANCE
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Document Creation Date:
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Publication Date:
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NATIONAL PHOTOGRAPHIC
INTERPRETATION CENTER
TECHNICAL
PUBLICATION
A RECOMMENDED COLOR VOCABULARY
FOR COLOR AERIAL RECONNAISSANCE
Declass Review by NIMA / DoD
CONFIDENTIAL
NPIC/R-02/72
JANUARY 1972
GROUP 1: 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 RECOMMENDED COLOR VOCABULARY FOR
COLOR AERIAL RECONNAISSANCE
January 1972
NATIONAL PHOTOGRAPHIC INTERPRETATION CENTER
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Page
SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vii
1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . 1
2.0 THE VISUAL PROBLEMS RELATED TO THE INTERPRETATION OF COLOR
IMAGERY . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1 THE COLOR-DISCRIMINATION CAPABILITIES OF THE AVERAGE COLOR-
NORMAL OBSERVER . . . . . . . . . . . . . . . . . . . . . . 3
2.2 THE COLOR-MATCHING CAPABILITIES OF THE AVERAGE COLOR-NORMAL
OBSERVER . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3 THE COLOR-MEMORY CAPABILITIES OF THE AVERAGE COLOR-NORMAL
OBSERVER . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4 THE COLOR-NAMING CAPABILITIES OF THE AVERAGE COLOR-NORMAL
OBSERVER . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.5 A SUMMARY OF THE VISUAL PROBLEMS RELATED TO THE INTERPRETA-
TION OF COLOR IMAGERY . . . . . . . . . . . . . . . . . . . . 11
3.0 THE PHOTOGRAPHIC PROBLEMS RELATED TO THE INTERPRETATION OF
COLOR IMAGERY . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1 PHOTOGRAPHIC SCALE AND ITS RELATIONSHIP TO THE ANGULAR SIZE
OF THE TARGET SEEN BY THE IMAGE INTERPRETER . . . . . . . . . 13
3.2 COLOR RENDITION IN THE PHOTOGRAPHIC PROCESS AND ITS RELATION-
SHIP TO THE COLOR VOCABULARY . . . . . . . . . . . . . . . . . 14
3.3 A SUMMARY OF THE PHOTOGRAPHIC PROBLEMS RELATED TO THE INTER-
PRETATION OF COLOR IMAGERY . . . . . . . . . . . . . . . . . . 27
4.0 THE MISSION OF THE CENTER AND THE FUNCTION OF ITS PERSONNEL. . 28
4.1 THE PERSONNEL OF THE CENTER AND THEIR ANTICIPATED COLOR
VOCABULARY RELATED PROBLEMS . . . . . . . . . . . . . . . . . 28
4.1.1 Image Interpreters . . . . . . . . . . . . . . . . . . 28
4.1.2 Collateral Researchers . . . . . . . . . . . . . . . . 29
4.1.3 Editors . . . . . . . . . . . . . . . . . . . . . . . 29
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TABLE OF CONTENTS (Continued)
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4.1.4 Model Makers . . . . . . . . . . . . . . . . . . . . . 29
4.1.5 Librarians . . . . . . . . . . . . . . . . . . . . . . 30
4.1.6 Scientists and Engineers . . . . . . . . . . . . . . . 30
4.1.7 Artists and Illustrators . . . . . . . . . . . . . . 30
4.1.8 Photographic Technicians . . . . . . . . . . . . . . . 31
4.1.9 Printers and Pressmen . . . . . . . . . . . . . . . . 31
4.1.10 Photogrammetrists . . . . . . . . . . . . . . . . . . 32
4.1.11 Managers . . . . . . . . . . . . . . . . . . . . . . . 32
5.0 DISCUSSION AND INITIAL EVALUATION OF VARIOUS COLOR SYSTEMS . . 33
5.1 COLOR SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . 33
5.1.1 The Munsell Color System . . . . . . . . . . . . . . . 33
5.1.1.1 The Concept and Description of the Munsell
System . . . . . . . . . . . . . . . . . . . . . 33
5.1.1.2 The Application of the Munsell Color System . . 34
5.1.1.3 The Advantages of the Munsell Color System . . . 34
5.1.1.4 The Disadvantages of the Munsell Color System . 34
5.1.2 CIE Color System . . . . . . . . . . . . . . . . . . . 36
5.1.2.1 The Concept and Description of the CIE Color
System . . . . . . . . . . . . . . . . . . . . . 36
5.1.2.2 The Application of the CIE Color System to
Color Imagery . . . . . . . . . . . . . . . . . 39
5.1.2.3 The Advantages of the CIE Color System . . . . . 39
5.1.2.4 The Disadvantages of the CIE Color System . . . 40
5.1.3 ISCC-NBS Color System . . . . . . . . . . . . . . . . . 41
5.1.3.1 The Concept and Description of the ISCC-NBS
Color System . . . . . . . . . . . . . . . . . . 41
5.1.3.2 The Application of the ISCC-NBS Color System
to Color Imagery . . . . . . . . . . . . . . . . 42
5.1.3.3 The Advantages of the ISCC-NBS Color System . . 42
5.1.3.4 The Disadvantages of the ISCC-NBS Color System . 42
5.1.4 Lovibond Color System . . . . . . . . . . . . . . . . . 45
5.1.4.1 The Concept and Description of the Lovibond
Color System . . . . . . . . . . . . . . . . . . 45
5.1.4.2 The Application of the Lovibond Color System
to Color Imagery . . . . . . . . . . . . . . . . 45
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TABLE OF CONTENTS (Continued)
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5.1.4.3 The Advantages of the Lovibond Color System . . 46
5.1.4.4 The Disadvantages of the Lovibond Color System . 46
5.1.5 Densitometric Munsell Color System . . . . . . . . . 47
5.1.5.1 The Concept and Description of the Densitometric
Munsell Color System . . . . . . . . . . . . . . 47
5.1.5.2 The Application of the Densitometric Munsell to
Color Imagery . . . . . . . . . . . . . . . . . 47
5.1.5.3 The Advantages of the Densitometric Munsell
Color System . . . . . . . . . . . . . . . . . . 48
5.1.5.4 The Disadvantages of the Densitometric Munsell
Color System . . . . . . . . . . . . . . . . . . 48
5.1.6 DIN Color System . . . . . . . . . . . . . . . . . . . 49
5.1.6.1 The Concept and Description of the DIN Color
System . . . . . . . . . . . . . . . . . . . . . 49
5.1.6.2 The Application of the DIN Color System to
Color Imagery . . . . . . . . . . . . . . . . . 49
5.1.6.3 The Advantages of the DIN Color System . . . . . 49
5.1.6.4 The Disadvantages of the DIN Color System . . . 51
5.1.7 Ostwald Color System . . . . . . . . . . . . . . . . . 51
5.1.7.1 The Concept and Description of the Ostwald
Color System . . . . . . . . . . . . . . . . . . 51
5.1.7.2 The Application of the Ostwald Color System
to Color Imagery . . . . . . . . . . . . . . . . 53
5.1.7.3 The Advantages of the Ostwald Color System . . . 53
5.1.7.4 The Disadvantages of the Ostwald Color System . 53
5.1.8 NuHue, Plochere, Ridgway, Maerz & Paul, Villalobos,
Textile Color Card Association, and Methuin . . . . . . 54
5.1.8.1 The Concept and Description of the NuHue,
Plochere, Ridgway, Maerz & Paul, Villalobos,
Textile Color Card Association, and Methuin
Color System . . . . . . . . . . . . . . . . . . 54
5.1.8.2 The Application of the NuHue, Plochere, Ridgway,
Maerz & Paul, Villalobos, Textile Color Card
Association, and Methuin Color System to Color
Imagery . . . . . . . . . . . . . . . . . . . . 54
5.1.8.3 The Advantages of the NuHue, Plochere, Ridgway,
Maerz & Paul, Villalobos, Textile Color Card
Association, and Methuin Color System to Color
Imagery . . . . . . . . . . . . . . . . . . . . 54
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TABLE OF CONTENTS (Continued)
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5.1.8.4 The Disadvantages of the NuHue, Plochere, Ridgway,
Maerz & Paul, Villalobos, Textile-Color Card
Association, and Methuin Color Systems . . . . . 55
6.0 CONCLUSIONS AND THE RECOMMENDED COLOR VOCABULARY . . . . . . . 56
6.1 THE CONCLUSIONS OF THE REVIEW OF THE PROBLEMS RELATED TO THE
DEVELOPMENT OF A COLOR VOCABULARY FOR THE CENTER . . . . . . . 56
6.2 THE CONCEPT OF A MULTILEVEL COLOR VOCABULARY . . . . . . . . . 58
6.3 SELECTION OF FIRST LEVEL COLOR VOCABULARY . . . . . . . . . . 60
6.4 THE RECOMMENDED COLOR VOCABULARY . . . . . . . . . . . . . . . 61
7.0 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . 63
FIGURE 2.1 THE STANDARD DEVIATIONS OF COLOR MATCHES BY OBSERVER
PGN, ENLARGED TEN TIMES ON THE 1931 CIE x, y CHROMA-
TICITY DIAGRAM . . . . . . . . . . . . . . . . . . . . 4
FIGURE 2.2 THE VARIANCES OF COLOR MATCHES-BY OBSERVER PGN,
ENLARGED TEN TIMES ON THE ~,n CHROMATICITY DIAGRAM . . 5
FIGURE 2.3 THE RELATIVE SIZES OF THE COLOR DISCRIMINATION
ELLIPSES FOR A 3' AND A 4.4? FIELD OF VIEW . . . . . . 7
FIGURE 2.4 A COMPARISON OF THE ACTUAL AND MEMORY COLORS FOR
SEVERAL FAMILIAR OBJECTS . . . . . . . . . . . . . . . 10
FIGURE 3.1 A NOMOGRAPH FOR DETERMINING THE ANGULAR SIZE OF AN
IMAGE ON THE OBSERVER'S RETINA WHEN GIVEN THE OPTICAL
MAGNIFICATION OF THE VIEWING INSTRUMENT AND THE SIZE
OF IMAGE ON THE FILM . . . . . . . . . . . . . . . . . 15
FIGURE 3.2 THE APPROXIMATE COLOR VOLUME OF EASTMAN KODAK'S SO-242
COLOR-REVERSAL ACQUISITION FILM . . . . . . . . . . . . 18
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LIST OF FIGURES (Continued)
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FIGURE 3.3 THE APPROXIMATE COLOR GAMUT OF EASTMAN KODAK'S SO-242
COLOR-REVERSAL ACQUISITION FILM . . . . . . . . . . . .
19
FIGURE 3.4 THE CHROMATICITY COORDINATES FOR THE COLORS OF SOME
SELECTED NATURAL AND CULTURAL OBJECTS AND THEIR
RELATIONSHIP TO THE COLOR GAMUT OF SO-242 . . . . . . .
21
FIGURE 3.5 THE MAGNITUDE AND DIRECTION OF THE COLOR SHIFTS
PRODUCED ON SO-242 BY DIFFERENT EXPOSURE CONDITIONS . .
25
FIGURE 5.1 THE CONCEPT OF THE MUNSELL COLOR SYSTEM . . . . . . . .
35
FIGURE 5.2 THE CIE COLOR SYSTEM . . . . . . . . . . . . . . . . .
37
FIGURE 5.3 THE ISCC-NBS HUE NAMES AND ABBREVIATIONS FOR A CONSTANT
MUNSELL VALUE OF SIX . . . . . . . . . . . . . . . . .
43
FIGURE 5.4 THE ISCC-NBS MODIFIERS FOR A PURPLE HUE . . . . . . . .
44
FIGURE 5.5 THE LINES OF CONSTANT DIN-FARBTON AND DIN-SATTIGUNG
PLOTTED ON A 1931 CIE DIAGRAM . . . . . . . . . . . . .
50
TABLE 3.1 THE CIE AND MUNSELL DESIGNATIONS FOR THE APPROXIMATE
COLOR GAMUT OF EASTMAN KODAK'S SO-242 COLOR REVERSAL
ACQUISITION MATERIAL . . . . . . . . . . . . . . . . . . 20
TABLE 3.2 THE CIE CHROMATICITY COORDINATES, LIGHTNESSES,
DOMINANT WAVELENGTHS, AND EXCITATION PURITIES FOR THE
COLORS OF SELECTED NATURAL AND CULTURAL TARGETS . . . . 22
TABLE 3.3 THE MUNSELL AND ISCC-NBS DESIGNATIONS FOR THE COLORS
OF SELECTED NATURAL AND CULTURAL TARGETS . . . . . . . . 24
TABLE 3.4 THE CIE CHROMATICITY COORDINATES FOR THE RED AND GREEN
TARGETS WHOSE IMAGES WERE EITHER PROPERLY EXPOSED,
OVEREXPOSED, OR UNDEREXPOSED DURING ACQUISITION . . . . 26
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bE,
The Center, in its preparation for the possible use of color
imagery, has seen a need for a standardized color vocabulary. Thus, the
objective of this study was to recommend a vocabulary that could be used
(1) to identify and designate the colors of objects or targets appearing
on color imagery, (2) to catalogue color-related target signatures, and
(3) to communicate color-related information.
The development of a color vocabulary was accomplished by
investigating a series of topics that are related to the Center's mission
of exploiting small-scale, high-quality color imagery. The following
topics were investigated:
(1) The visual problems related to the interpretation of color
imagery:
The color-discrimination capabilities of the
average color-normal observer
? The color-matching capabilities of the average
color-normal observer
? The color-memory capabilities of the average
color-normal observer
? The color-naming capabilities of the average
color-normal observer.
(2) The photographic problems related to the interpretation of
color imagery:
? Photographic scale and its relationship to the
angular size of the target seen by the image
interpreters
? Color rendition of the photographic process and
its relationship to the color vocabulary.
(3) The anticipated job-related color vocabulary needs of the
staff:
? Image interpreters
? Collateral researchers
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? Editors
? Model makers
? Scientists and Engineers
? Artists and Illustrators
? Photographic Technicians
? Printers and Pressmen
? Photogrammetrists
? Managers.
(4) The basic concepts, methods of application, and the advan-
tages and disadvantages of the systems used to designate,
specify, or identify different colors:
? Munsell
? CIE
? ISCC-NBS
? Lovibond
? Densitometric Munsell
? DIN
? Ostwald
? NuHue
? Plochere
? Ridgway
? Maerz & Paul
? Textile Color Card Association
? Methuin
? Villalobos.
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It was concluded from the results of the four topics studied
above that the needs of the Center could be satisfied by a trilevel color
vocabulary. The first level of this recommended color vocabulary consists
of seventeen names: pink, red, orange, brown, yellow, yellow-green, olive,
green, blue-green, blue, violet, purple, white, gray, black, cyan, and
magenta, and the modifiers, light and dark. Combinations of these color
names (except cyan and magenta which are not to be used for image colors)
such as red-brown can be used in those few situations where the single names
are not adequate to describe the colors. Samples of these colors (except
white, gray, and black) are included in the back of this report. The
second level of the color vocabulary consists of the Munsell and ISCC-NBS
color systems. The degree of precision needed in the visual communication
of color-related information determines which of these two color systems
are to be used. The ISCC-NBS color system is used when a non-precise
visual color reference is required for communication. This system is
implemented in normal working and viewing conditions, since the widely
separated color samples do not require the use of critical color matching.
When a more precise visual color reference is required, the Munsell system
is used. All Munsell color matches or designations are made visually,
under specified and well-controlled viewing conditions by highly-trained
personnel. The third level of the color vocabulary consists of the CIE
color-designation system for very precise and accurate color communication.
However, to implement this third level, it is necessary to develop a color
correction model to account for the effect of acquisition and processing on
color fidelity.
In addition, it is recommended that the Center develop the
capability for performing accurate and reliable color measurements by
forming a colorimetric group.
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The Center, in its preparation for the possible future use of
color imagery, has seen a need for a standardized color vocabulary. The
need for such a vocabulary can be fully appreciated when one tries to
read and understand a report which contains color names such as Robin's
Egg Blue and Sea Foam Mist. The actual colors these names represent are
unclear to all, including those individuals who initially suggested
their use. Because of the wide distribution of the information generated
by the Center and the credibility given to this information, it is
important that the Center have ready for future use a standardized color
vocabulary whose terms are clearly understood by all those who might use
the information published by the Center. Thus, the objective of this
study was to recommend a vocabulary that could be used (1) to identify
and designate the colors of objects or targets appearing in color imagery,
(2) to catalogue color-related target signatures, and (3) to communicate
color-related information.
The development of a color vocabulary was accomplished by in-
vestigating a series of topics that are related to the Center's mission
of exploiting small-scale, high-quality color imagery. The following
topics were investigated:
(1) the visual problems related to the interpretation of
color imagery
(2) the photographic problems related to the interpretation
of color imagery
(3) the job-related color needs of the Center's staff
(4) the methods used to designate, specify, or identify
different colors.
A detailed analysis of each of these topics can be found in
Sections 2.0, 3.0, 4.0, and 5.0 of this report.
The color vocabulary that is being recommended for use by the
Center was based on the conclusions reached by these investigations and
is discussed in Section 6.0 at the end of this report.
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2.0 THE VISUAL PROBLEMS RELATED TO THE
INTERPRETATION OF COLOR IMAGERY
The ability of the average color-normal observer to accomplish
various color-related visual tasks was considered to be one of the major
factors in determining the type of vocabulary that might be used by the
Center. Special emphasis has been placed on the visual aspects of color
because nearly all of the tasks require the image interpreters, the
photoscientists, or other individuals to examine the imagery visually
and then make some judgment, comment, or decision. With the introduction
of color, it is anticipated that the Center's personnel will continue to
perform all their present tasks as well as some new color-related tasks.
For example, the image interpreter might be expected to name the colors of
objects that appear in the imagery in addition to the identification and
enumeration of these objects. Thus, the type of color vocabulary that
might be used depends in part on the ability of an observer to perform
certain types of visual tasks such as color-naming and color-matching.
Unfortunately, much of the reported experimental data that have
been collected on the color capabilities of the average color-normal
observer were collected by using a few color-normal subjects who viewed
structure-free colored areas under very controlled viewing conditions.
It has been possible in such carefully controlled experiments to determine
a one-to-one correspondence between the physical stimuli (e.g., intensity,
wavelength, angular size of field) that were presented to the subject and
the visual impression (e.g., name of color, apparent size, saturation)
these physical stimuli created for the subject. Although much of this
information that is contained in the literature on the subject of color
perception may not be directly applicable to the Center's problems, it
can be used as a guide for determining the general range and nature of
the color capabilities or color-related skills of an average color-normal
observer.
The color capabilities or color-related skills of the average
color-normal individual that are of primary importance to the Center are
the following:
1. Discrimination
2. Matching
3. Memory
4. Naming
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These four categories are directly applicable to the development of a
color vocabulary for the Center. Furthermore, the measure of the ability
of the subject to perform one or more of the above tasks (i.e., discrimin-
ation, memory) includes the effects of secondary perceptual problems such
as after-images, simultaneous color contrast, color constancy, and
adaptation due to lighting conditions. A detail analysis of the color-
discrimination, color-matching, color-memory, and color-naming capabilities
of the average color-normal individual are given in Sections 2.1, 2.2, 2.3,
and 2.4 respectively.
2.1 THE COLOR-DISCRIMINATION CAPABILITIES OF THE AVERAGE COLOR-NORMAL
OBSERVER
The term color discrimination is used to designate or denote
the ability of the average color-normal observer to distinguish between
colors that differ in some combination of hue, saturation, and lightness.
The color-discrimination ability of a typical color-normal observer is
shown in Figure 2.1 and Figure 2.2. Although these data were collected
by using a single observer and at a constant lightness level, they are
quite representative of the other color-discrimination data that have been
collected by using several experimental subjects. The size of these
color-discrimination ellipses as plotted on the CIE diagram can be used
as a measure of the color-discrimination ability of the average color-
normal observer. It has been estimated on the basis of the size of these
ellipses that the average color-normal can distinguish differences between
approximately 7,000,000 colors.
The color-discrimination ability of the average color-normal
observer as indicated by the size of the ellipses shown in Figures 2.1
and 2.2 also depends on the viewing conditions under which the observer
made his color matches or discriminations. The sizes of the ellipses in
Figures 2.1 and 2.2 do not change significantly as the luminance levels
of the test and matching fields are varied from approximately 1 to 15
footlamberts. The size of the ellipses increases, i.e., color-
discrimination ability decreases, when the luminance levels drop below
approximately 1 footlambert. Although there is no direct experimental
verification, it is expected that the size of the ellipses will remain
nearly constant as the luminance levels are increased to as high as
several hundred footlamberts. The size of these ellipses decrease, i.e.,
color-discrimination ability increases, when the angular size of the field
of view increases. The color-discrimination ability of the average
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luminance level of 15 foot-
lamberts
0.4 0.6 0.8
x
FIGURE 2.1 THE STANDARD DEVIATIONS OF COLOR MATCHES BY OBSERVER PGN,
ENLARGED TEN TIMES ON THE 1931 CIE x, y CHROMATICITY
DIAGRAM (MacAdam, 1942) (see Section 5.1.2)
Note: The ellipses are for a
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0 0
o 0 p o
o 0 o 00 o
0 o
0
0 o v o
0 0
0
0
0
700 800 900 1000 1100
FIGURE 2.2 THE VARIANCES OF COLOR MATCHES - BY OBSERVER PGN, ENLARGED TEN TIMES ON
THE CHROMATICITY DIAGRAM. (MacAdam, 1971)(see Section 5.1.2)
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observer steadily deteriorates as his field of view is decreased below
1 to 2 degrees. Reliable data have not been collected for fields of view
whose angular subtense was less than 3 minutes.
The color-discrimination ellipses for a 3-minute and a 4.40-
degree size field of view are shown in Figure 2.3.
The color of the surround has a noticeable effect on the
ability of a color-normal observer to discriminate between slightly
different colors. This effect is more pronounced when the angular size
of the matching and test fields are quite small. For either large or
small comparison fields, the color-discrimination ability is greater
when the color of the surround is approximately the same as the two colors
the subject must discriminate between or match. Therefore, the color
discrimination ability of the average observer is more minimal when the
color of the surround is the complement of the colors being matched.
The ability of the average color-normal observer to distinguish
between spatially separated colors has not been thoroughly studied.
However, it is expected that this ability will rapidly decrease as the
angular separation between the colors increases.
The general conclusion is that the average individual has a
tremendous ability to distinguish between different colors; however, the
accuracy and precision with which these discriminations can be made is
very dependent upon the viewing conditions. Thus, any color vocabulary
must consider not only the discriminatory powers of the human visual
system but also its dependence upon the viewing conditions being used by
the observers. In addition, at least part of the vocabulary must be able
to designate large numbers of colors.
(MacAdam, 1971; MacAdam, 1959; Bedford and Wyszecki, 1958)
2.2 THE COLOR-MATCHING CAPABILITIES OF THE AVERAGE COLOR-NORMAL OBSERVER
The color-matching capability of the average color-normal
individual is a measure of his ability to select from a large collection
of different colors the one color that has the same or nearly the same
hue, saturation, and lightness as a given test sample. The color matches
made by a person who is a color normal will be valid only for those
viewing conditions that are equivalent to those that existed when the
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turi
4.4? Field of View
(ellipses enlarged 3-1/3 times)
0.61- (,s 3' Field of View
(ellipses enlarged 3-1/3 times)
FIGURE 2.3 THE RELATIVE SIZES OF THE COLOR-DISCRIMINATION ELLIPSES
FOR A 3' AND A 4.4? FIELD OF VIEW AND A CONSTANT
LIGHTNESS. (MacAdam, 1959)(see Section 5.1.2)
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match was made. For example, if any of the viewing parameters such as
the spectral distribution of the light source, the angular size of the
observer's field of view, or the color of the surround are changed, then
the original match between the two colors may no longer be valid. Further-
more, the textures of the colors being matched must be the same or nearly
so. Although the chromaticity coordinates for the color of a shiny piece
of red plastic may be the same as the chromaticity coordinates for the color
of rough, red brick, their visual appearance will be quite different.
Even when these viewing conditions are carefully controlled, there
will be differences between the matches made by a group of color-normal
individuals. Similarly, there will be considerable day-to-day variations
in the color matches made by a given individual even if he is trying to
match the same set of standard colors. R. M. Evans (Evans, 1948) has
estimated that a perfect match between two colors by an average color-
normal observer would probably be unsatisfactory for approximately ninety
percent of all other observers. -This variability among matches made by
observers is a result of the extreme sensitivity of their eyes to very
small differences in color. These variations can be reduced by controlling
and carefully monitoring the viewing conditions and matching techniques
that are used.
Much of the data that have been reported on color matching was
collected by having a color-normal observer adjust the color in one-half
of a bipartite field until it matched the test color appearing in the
other half of the field. An analysis of the data collected during the
course of such experiments indicated there was more variance in binocular
color matches than there was in the monocular color matches. Therefore,
monocular color matches may be preferable.
Color-matching experiments also have been conducted to determine the
variability between the successive and simultaneous methods. When the
simultaneous method is used, the test field or test color is visible while
the subject is adjusting the color of the matching field. When the suc-
cessive method of color matching is used, the subject first views the
test color for a given period of time. It is then blanked from his field
of view and after a predetermined period of time, the subject adjusts the
color of the test field to match what he remembers as being the test
color. This latter method is very similar to the way one matches colors
in his everyday activities. The successive method takes less time but
yields a greater variability in repeated matches of the same colors. Also,
those matched tend to be much higher in both saturation and lightness
than the matches made by the simultaneous method. It would appear that
simultaneous matching should be used.
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These color-matching problems place some constraints on the type
of vocabulary that might be used by the Center. For example, if each image
interpreter were going to read out the colors of every target he sees in
the imagery by using some type of a matching scheme, then every light
table and viewing instrument at the Center would have to provide their
users with the same illumination, angular-size of the field of view,
color of the surround, etc.. Furthermore, the texture of colors used by
the observer to match the colors of the targets should be the same. This
would require a set of standard vocabulary colors of approximately the
same granular structure as the color imagery. The use of monocular view-
ing for color matching should present no real problems in the modification
of existing viewing equipment. The use of simultaneous rather than suc-
cessive matching might produce some problems in the modification of
present viewing systems in that some type of split-field viewer would be
required. In general, the extreme sensitivity of the eye to very small
differences in color indicates that a large commitment in terms of both
manpower and money must be made if the vocabulary to be used requires that
each image interpreter read out the target's color by some kind of
color-matching scheme. (Newhall, Burnham, and Clark, 1957; Hoffman, 1962;
Wyszecki and Stiles, 1967; Evans, 1948; Hunt, 1965)
2.3 THE COLOR-MEMORY CAPABILITIES OF THE AVERAGE COLOR-NORMAL OBSERVER
Color memory is the term used to describe the ability of an
average color-normal observer to recall and correctly identify the colors
of familiar objects. It is indicated by an analysis of the data collected
during several experiments that the memories of most individuals are quite
unreliable and highly variable. In most cases, the characteristic
chromatic attribute of the color of the object was usually exaggerated
when recalled from memory. The colors of familiar objects were remembered
as being lighter and more saturated. For example, the typical observer
remembers the sky as being bluer, the grass as being greener, and the
bricks as being redder than the colors indicated by the chromaticity values
for these same objects. Similarly, in these experiments, bright objects
were remembered as being brighter than they actually were, and dark objects
as being darker. Figure 2.4 shows the magnitude and direction of the
differences between the chromaticity coordinates for the object and those
colors selected by memory. Remembered colors will usually 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.
There are some indications that the color memory of the observer can be
improved by training and a considerable amount of practice. If color
memory is to be used, then a color vocabulary must be simple and limited
to a few colors to compensate for the unreliability.
(Bartleson, 1960; Hanes and Rhoades, 1959; Newhall, Burnham and Clark, 1957)
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04
r Evergreens
KEY
Noted Memory-
object color
Soil
Ilk.ri*a tG
21 "e={{OSA Zenith sky)
/ 24 32
i
Red brick
FIGURE 2.4 A COMPARISON OF THE ACTUAL AND MEMORY COLORS FOR
SEVERAL FAMILIAR OBJECTS (Bartleson, 1960)
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2.4 THE COLOR-NAMING CAPABILITIES OF THE AVERAGE COLOR-NORMAL OBSERVER
The color-naming ability of an average color-normal observer is a
measure of his ability to identify a given color without using a reference
system (i.e., using absolute judgment). An analysis of the data collected
in experiments which used nearly monochromatic lights indicated that the
average untrained color-normal observer can reliably name only ten to twenty
basic colors without recourse to a color-reference system. Similarly, the
results of experiments performed by using Munsell chips of various hue,
chroma, and value have indicated that a trained and highly motivated indivi-
dual could reliably name, without using a reference system, the order of
fifty or more colors. The maintenance of this level of proficiency required
the subject to practice approximately one hour a day naming the Munsell
chips used in the experiment. Based on these results and certain theoreti-
cal considerations, it has been predicted that a trained person who had
normal color vision would be able to do as well.
The analysis of this information indicates that a color vocabulary
would have to be limited to fifteen to twenty words, if some kind of color-
reference system were not used. A larger vocabulary, which might contain
fifty or more words, would require too much time and effort to learn to use
on a routine basis.
(Halsey and Chapanis, 1951; Hanes and Rhoades, 1959; Chapanis, 1965;
Halsey, 1959)
2.5 A SUMMARY OF THE VISUAL PROBLEMS RELATED TO THE INTERPRETATION OF
COLOR IMAGERY
The visual. problems related to the interpretation of small-scale,
high-quality color imagery have been discussed earlier in this section of
the report. From the experimental results presented in these discussions,
it is evident that under well-controlled viewing conditions, the average
color-normal individual has a tremendous capacity to accurately and
reliably discriminate differences between, i.e., by comparative judgment,
the colors of two structure-free fields. The accuracy and precision of
these judgments made by the average observer will deteriorate rapidly if
the viewing conditions are not well controlled and maintained. Never-
theless, even with poorly controlled viewing conditions, the accuracy and
reliability of the comparative judgments will probably be greater than his
color memory or any absolute color judgments made by the same observer.
However, his color memory can be improved by training and frequent practice
of the exercises. On the basis-of this evidence, it is concluded that a
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color vocabulary which consists of more than fifteen to twenty different
colors must be used with some type of visual color-reference system.
Furthermore, the viewing conditions for using this visual color-reference
system must be clearly specified, understood, and used. In addition, the
color vocabulary must be able to designate a large number of colors because
of the color-discrimination ability of the typical observer.
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3.0 THE PHOTOGRAPHIC PROBLEMS RELATED TO
THE INTERPRETATION OF COLOR IMAGERY
In addition to the visual problems that were discussed in
Section 2.0, the type of color vocabulary that might be used by the Center
will in part be determined by the photographic scale and color fidelity
4 of the imagery. As will be discussed in Section 3.1, the photographic
scale, which is the ratio of the focal length to the altitude of the
acquisition system, is the acquisition parameter that determines the
angular size of the image to be viewed. Thus, the photographic scale is
related to the expected color-discrimination performance because, as dis-
cussed in Section 2.0, that ability is related to the angular size of the
image to be viewed. The color-rendition or color-fidelity characteristics
of the imagery that are used is important to the development of the color
vocabulary because it helps to specify both the nature and size of the
color tolerances that will be required. The color-fidelity or color-
rendition problems that are related to color imagery are discussed in
Section 3.2.
3.1 PHOTOGRAPHIC SCALE AND ITS RELATIONSHIP TO THE ANGULAR SIZE OF THE
TARGET SEEN BY THE IMAGE INTERPRETER
Photographic scale is expressed as the ratio of the focal length
to the altitude of the acquisition camera. This ratio determines the
image size of the targets being photographed. For example, imagery ac-
quired from an altitude of 10,000 feet with a 6-inch focal-length lens
would have a photographic scale of 1:20,000. At this scale, the length of
an image of an automobile or any other object whose ground size was 16
feet in length would be 0.0096 in or 0.240 mm.
The image size of targets is one of two factors that determine
the angular size of the image seen by the image interpreter or other ob-
server. The optical magnification of a viewing instrument such as a
stereoviewer is the second factor. As would be expected, the angular size
of the object being viewed increases as the observer increases the optical
magnification of the viewer. The relationship between the angular size
of the image, the size of the object being viewed in the imagery, and
the total optical magnification of the viewing instrument can be expressed
as:
6 = 0.229 MS
13
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(1)
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where 6 is the angular size of the image in degrees, M is the total optical
magnification of the viewing system, and S is the dimension of the image in
millimeters.
The relationship expressed in Equation (1) is summarized in the
nomograph shown in Figure 3.1. The dotted line indicates the angular size
of the image would be 2? if it were the image of a 6-meter (19.7-foot)
ground object that had been photographed at 20,000 feet with a 6-inch lens
and was being viewed at an optical magnification of 60x. Because of the
linear nature of Equation (1), the image of a 5-foot object photographed
and viewed under the same conditions would have an angular size of approxi-
mately one-half a degree (1/2?).
Although the angular size of the image being viewed can be
increased by increasing the total optical magnification, this method is
limited by the granular nature of the dye deposits which are formed in
the film. It is anticipated that the granular nature of color imagery
used by the Center would limit the optical magnification that could be
routinely and easily used by the image interpreters to a maximum of
approximately 60x. By using 60x as a working upper limit and the nomo-
graph in Figure 3.1, it is evident that all images whose dimensions are
less than 0.15 millimeters will have an angular size of less than 2
degrees.
As was discussed in Sections 2.1 and 2.2, the color discrimination
and matching ability of the average color-normal individual is quite
dependent upon the angular size of the colored areas that he is trying to
distinguish between or match together as well as the luminance levels. A
1 to 2 degree field of view is desired for accurate and reliable color
matching. At a photographic scale of 40,000:1 and viewing magnification
of 60x, a 2? field of view corresponds to a ground length of approximately
20 feet, and a 1/2? field of view corresponds to a ground length of
approximately 5 feet. Thus, the images of most of the targets that may be
of interest to the Center will have angular sizes of less than the desired
1 to 2 degrees; therefore, a color vocabulary that might be used by the
Center should not require the image interpreter to make very accurate
visual color matches or to visually discriminate between a large number
of nearly identical colors.
3.2 COLOR RENDITION IN THE PHOTOGRAPHIC PROCESS AND ITS
RELATIONSHIP TO THE COLOR VOCABULARY
"Color fidelity" is a term used to describe the ability of
a color-reproduction process to accurately reproduce the colors in
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90
F
FIGURE 3.1 A NOMOGRAPH FOR DETERMINING THE ANGULAR SIZE OF AN IMAGE ON
THE OBSERVER'S RETINA WHEN GIVEN THE OPTICAL MAGNIFICATION
OF THE VIEWING INSTRUMENT AND THE SIZE OF IMAGE ON THE FILM
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the original scene. The color fidelity of a process is sometimes assessed
by using some numerical measure which is related to the size of the differ-
ences between the chromaticity coordinates of the colors in the original
scene and the chromaticity coordinates of their reproduction in the imagery.
Nevertheless, it should be remembered that even if the colors in the origi-
nal scene have the same chromaticity coordinates as the colors in the re-
production, the colors may appear to be different because of differences
in the surface textures.
The color-fidelity or color-rendering properties of a photographic
process also are controlled by both the spectral sensitivity of the various
layers in the conventional tripack emulsion and the spectral transmittance
of the dyes that are formed during development. In.technical litera-
ture there are many complete and detailed discussions of how the color
fidelity of a color process is related to both the red, blue, and green
sensitivity of the tripack emulsion and spectral transmittance of the
magenta, cyan, and yellow dyes that are formed in the emulsion during the
processing of the exposed film. However, these details of the theory as
they apply to a color-reversal film such as SO-242 or SO-255 are not en-
tirely applicable to the color vocabulary and are too complicated to dis-
cuss in this report. In general, a color process that faithfully repro-
duces all the colors in the scene can not be made by using real (i.e.,
physically realizable) dyes and spectral sensitizers. Even when the photo-
chemist is working with real dyes and spectral sensitizers, he must com-
promise between the color-rendering properties of the color reproduction
process and such practical considerations as resolution, shelf-life, and
cost. Thus, even if there were no color degradation due to factors such
as the atmospheric haze and clouds, the colors of objects seen in the
imagery are, at best, only close approximations to the colors of the
objects.
Color-reversal films such as SO-242 and SO-255, which are made
with real spectral sensitizers and dyes, can not. reproduce all the colors
that appear on the CIE chromaticity diagram. The gamut of those colors
that can be reproduced by the film is of importance to the development of
a color vocabulary because it delineates the range of colors that must be
covered by the vocabulary. Because of the tridimensional nature of color,
the color gamut of a color process is defined as the volume formed by the
locus of points representing the chromaticity coordinates (x, y) and the
lightness value (Y) of the various colors that can be formed by specific
combinations of the available amounts of the colorants used in the process.
In photography, the color gamut of a film or a process is generally
specified by the locus of points that represent the chromaticity coordi-
nates of the colors formed by the various combinations of 3.0 END
(equivalent neutral density) concentrations of the cyan, magenta, and
yellow dyes used in the process. The expected color gamut or color
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volume for SO-242 or SO-255 is shown in Figure 3.2; the projection of this
color volume onto the regular 1931 CIE chromaticity diagram is shown in
Figure 3.3; and the numerical values for the data plotted in Figure 3.2
and 3.3 are tabulated in Table 3.1.
Of importance to the development of the color vocabulary is how
many of the colors of natural and cultural objects will have chromaticity
coordinates that, when plotted on the CIE diagram., will be contained within
the color gamut that has been calculated for a film such as SO-242. In
Figure 3.4, the chromaticity coordinates for colors of some selected
natural and cultural objects and the color gamut of SO-242 have been
plotted on a 1931 CIE chromaticity diagram. These values also are listed
in Tables 3.2 and 3.3. As shown in Figure 3.4, all the coordinates for
the colors are contained within the color gamut of SO-242. This means
that the colors of objects appearing in the imagery acquired with SO-242
will not be grossly distorted.
In addition.to those inherent film problems (e.g., unstable dyes),
which degrade the color fidelity of the imagery, there are many other
opportunities for degrading the color fidelity of the imagery during the
acquisition and processing phases of a mission. An example of the magni-
tude and direction of the color shifts caused by a variation in exposure
is shown in Figure 3.5. For these calculations of the color shifts re-
sulting from variations in exposure, it was assumed that the proper ex-
posure was that which would accurately reproduce grays or achromatic colors
in the scene. As is shown in Figure 3.5, an over-exposure tends to
desaturate and increase the lightness of the colors, and an under-exposure
tends to produce darker colors of a higher saturation. A shift in the
dominant wavelength was produced by both the underexposure and the
overexposure. Color shifts of an equivalent size and magnitude also can
be caused by variations in atmospheric conditions and sun angle.
When the magnitude of the color shifts that are illustrated in
Figure 3.5 is compared to the lOx enlarged color discrimination ellipses
in Figure 2.1, it is quite obvious that very small variations in the
exposure conditions will produce color shifts that are readily percept-
ible to the average color-normal observers. Thus, a color vocabulary that
might be used by the Center must take into account the color shifts that
are caused by variations in the acquisition and processing phases of a
given mission. Furthermore, the color vocabulary as a means of reporting
out and cataloguing target signatures must also account for the color
variations that will occur on a mission-to-mission basis. Thus, color
correction formulas will have to be developed.
(Bergner, Gelbke, and Mehliss, 1966; Evans, Hanson, and Brewer, 1953;
Slayter, 1970; Wyszecki and Stiles, 1967; Hunt, 1967)
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loo M , Magenta
Y , Yellow
C , Cyan
The numbers indicate
80 the equivalent neutral
density (END) of the dyes
FIGURE 3.2 THE APPROXIMATE COLOR VOLUME OF EASTMAN KODAK'S SO-242 COLOR
REVERSAL ACQUISITION FILM
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0 0.2 0.4 0.6
x
M, Magenta
Y) Yellow
C, Cyan
Numbers indicate the
equivalent neutral
densities (END) of the
dyes
01 V \ il0- 1 1
FIGURE 3.3 THE APPROXIMATE COLOR GAMUT OF EASTMAN KODAK'S
SO-242 COLOR-REVERSAL ACQUISITION FILM
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TABLE 3.1 THE CIE AND MUNSELL DESIGNATIONS FOR THE
APPROXIMATE COLOR GAMUT OF EASTMAN KODAK'S
SO-242 COLOR REVERSAL ACQUISITION MATERIAL
Color of Dye
END
x
CIE
y
y
Munsell
H V C
Yellow
.425
.461
.817
lOY 9/10
Yellow
.504
.485
.628
2.5Y 8/22
Cyan
.217
.281
.579
2.5B 8/10
Cyan
.157
.231
.309
5B 6/10
Magenta
.308
.188
.298
7.5P 6/18
Magenta
.320
.104
.069
10P 3/24
Cyan + Yellow
1.0
.307
.491
.439
LOGY 7/10
Cyan + Yellow
3.0
.286
.653
.114
LOGY 4/14
Cyan + Magenta
1.0
.195
.135
.143
7.5PB 4/16
Cyan + Magenta
3.0
.148
.029
.011
7.5PB 1/22
Magenta + Yellow
1.0
.483
.341
.253
7.5R 5/4
Magenta + Yellow
3.0
.719
.270
.047
7.5R 3/18
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The Approximate Color Gamut of
SO-242
FIGURE 3.4 THE CHROMATICITY COORDINATES FOR THE COLORS OF SOME
SELECTED NATURAL AND CULTURAL OBJECTS AND THEIR
RELATIONSHIP TO THE COLOR GAMUT OF SO-242
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TABLE 3.2 THE CIE CHROMATICITY COORDINATES, LIGHTNESSES, DOMINA2T 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 run
Pe, %
Source
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)
"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)
"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.)
D
r
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TABLE 3.2 THE CIE CHROMATICITY COORDINATES, LIGHTNESSES, DOMINANT WAVELENGTHS, AND
EXCITATION PURITIES FOR THE COLORS OF SELECTED NATURAL AND CULTURAL
TARGETS (Continued)
Chromaticity Lightness Dominant Excitation
Type of Coordinates Value Wavelength Purity CIE Standard
Sample x y Y, 7 a d nm Pe, 7 Source
29.
Outer Bark, White Oak (Quercus alba,
L.)
0.326
0.342
27.7
571.1
11.1
C
30.
Inner Bark, White Oak (Quercus alba,
L.)
0.357
0.350
7.5
580.2
'23.1
C
31.
Chinese Red #6335 Chi-namel Paint,
Chi-namel Paint and Varnish Co.
0.556
0.330
16.5
609.4
69.5
C
32. Colony Yellow #317 House Paint,
0.379
0.391
68.5
576.5
38.4
C
Lowe Brothers
33. Green #173 Tractor Paint, Lowe
Brothers
0.268
0.339
6.8
497.6
14.2
C
34. Red #139 Tractor Paint, Lowe
0.514
0.321
10.7
613.2
55.8
C
Brothers
35. Royal Blue Permanent Trim Paint,
0.221
0.234
10.0
478.8
41.6
C
John W. Masury & Son
36. Seal Brown Supreme House Paint,
John W. Masury & Son
0.378
0.343
8.2
590.3
25.4
C
37. Verdi Green #6830 Super House Paint,
Chi-namel Paint and Varnish Co.
0.256
0.400
30.7
511.1
18.6
C
38. Khaki #1 (cotton)
0.368
0.366
24.7
579.7
28.9
C
39. Olive Drab #52 (wool)
0.378
0.379
10.3
578.6
35.1
C
40. US Marine Corps Necktie
0.371
0.362
19.9
581.6
28.5
C
41. US Marine Corps Overseas Cap (summer)
0.377
0.371
19.0
580.4
32.7
C
42. US Marine Corps Pants (summer)
0.368
0.364
21.6
580.3
28.3
C
43. US Marine Corps Shirt (summer)
0.368
0.372
23.2
578.2
30.4
C
44. US Marine Corps Overseas Cap (winter)
0.329
0.345
5.4
572.0
12.8
C
45. US Marine Corps Blouse (winter)
0.327
0.347
5.3
569.7
12.8
C
46. US Marine Corps Pants (winter)
0.329
0.344
6.0
572.3
12.5
C
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TABLE 3.3 THE MUNSELL AND ISCC-NBS DISIGNATIONS FOR THE COLORS OF
SELECTED NATURAL AND CULTURAL TARGETS
Type of
Sample
ISCC-NBS Color
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 virginiana,
Mill.)
29.
Outer Bark, White Oak (Quercus alba, L.)
0.9GY
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 -F6335 Chi-namel Paint,
Chi-namel Paint and Varnish Co.
7.2R
4.6/13.3
Vivid Reddish orange
32.
Colony Yellow #317 House Paint,
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,
John W. Masury & Son
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 452 (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.
US Marine Corps Overseas Cap (winter)
O.1GY
2.7/0.8
Olive gray
45.
US Marine Corps Blouse (winter)
1.8GY
2.7/1.0
Olive gray
46.
US Marine Corps Pants (winter)
10.OY
2.9/0.9
Olive gray
I-
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? Proper Exposure or E
A I - Stop Underexposure or E = O.5E.
x A 1/2-Stop Overexposure or E = 1.5E.
Exposure Source-Photographic Daylight D5500
Viewing Source- CIE Standard Source C
(See Table 3.4 for numerical values.)
FIGURE 3.5 THE MAGNITUDE AND DIRECTION OF THE COLOR SHIFTS
PRODUCED ON SO-242 BY DIFFERENT EXPOSURE CONDITIONS
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TABLE 3.4 THE CIE CHROMATICITY COORDINATES FOR THE
RED AND GREEN TARGETS WHOSE IMAGES WERE
EITHER PROPERLY EXPOSED, OVEREXPOSED, OR
UNDEREXPOSED DURING ACQUISITION
Color of the Target
Chromaticity
Lightness
Value*,
and Exposure Conditions
Coordinates*
percent
Green target-correct exposure
0.34
0.44
36
Green target-1 stop underexposure
0.31
0.56
13
Green target - 1/2 stop overexposed
0.31
0.42
47
Red target-correct exposure
0.57
0.35
12
Red target-1 stop underexposure
0.65
0.29
4
Red target-1/2-stop overexposure
0.51
0.34
17
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3.3 A SUMMARY OF THE PHOTOGRAPHIC PROBLEMS RELATED TO THE INTERPRETATION
OF COLOR IMAGERY
Some of the photographic problems of small-scale color imagery,
which were considered to be relevant to the color vocabulary, have been
discussed in this section of the report. Images of targets expected to
be of interest to the Center would have an angular size of less than two
degrees when viewed at the maximum useable magnification. Fields of
view whose angular sizes are the order of two degrees or larger are con-
sidered necessary for accurate and reliable color matching or color discri-
mination. Therefore, it is concluded that because of the small angular
size of the targets of interest it will be difficult to use a visual
matching technique to reliably determine the colors of an image.
The color fidelity of imagery acquired by using acquisition films
such as SO-242 or SO-255 has also been discussed. It was stated that the
color fidelity or color-rendering properties of color reversal films such
as SO-255 or SO-242 were degraded because the photochemist also had to
consider factors such as resolution, dye stability, and cost in his
selection of the sensitizers and the colorants. It was shown in Section
3.1 that noticeable color shifts or color variations can result from small
changes or variations in exposure. Similarly, color shifts of the same
magnitude can be expected for variations in other acquisition factors such
as sun angle and atmospheric conditions over the target. It is apparent
from these results that, at best, the image colors will be only close ap-
proximations to the actual or "ground-truth" colors of these objects. It
also is apparent that the image colors of an object will vary on a mission-
to-mission basis if not on a frame-to-frame basis. Thus, any accurate
measurement of the image color will be only an approximation to the actual
color. It is concluded that any color vocabulary that might be used by
the Center must be capable of accounting, in some way, for these variations
in the image color of a target if the actual color is to be determined.
Furthermore, the ground-truth color of a target can not be determined
solely from the information that can be extracted from the imagery because
both the photography and color are integrating processes. To determine
the actual color of an object, the image interpreter or photoscientist
must use some type of an acquisition model which includes and accounts
for such variables as sun angle and atmospheric effects. Hence, one of
the outputs of the color vocabulary should be color-related data that can
be used as an input to an acquisition model which would be used to de-
termine the actual color of the object.
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The Center is an operational organization whose mission is to
transform information in the form of photographic images into words and
numbers that can be used by other individuals and organizations. Because
of the operational nature of the Center, the speed and accuracy with
which it fulfills its assigned mission is of primary importance. To aid
in the fulfillment of this mission, the Center has become a highly self-
contained and self-sufficient organization employing people with a great
diversity of backgrounds and skills. Thus, any color vocabulary that is
going to be used successfully by the Center must be applicable to most
of the job-related color needs of a very diversified group of individuals.
To aid in the development of the color vocabulary, a very simple
job analysis was performed to delineate the anticipated job-related color
needs of the various members of the staff who might be involved in all or
some aspects of any future exploitation of color imagery. The anticipated
needs were determined by examining what the staff now does to aid in the
exploitation of conventional black and white imagery and what it might be
expected to do to assist in the exploitation of color imagery. The ob-
servations and conclusions of this simplified job analysis are discussed
in the following sections. The significance of these job-related problems
to the development of the color vocabulary is considered in Section 6.0.
4.1 THE PERSONNEL OF THE CENTER AND THEIR ANTICIPATED COLOR VOCABULARY
RELATED PROBLEMS
4.1.1 Image Interpreters
In the exploitation of conventional black and white imagery,
the image interpreter has two principal funtions: (1) the identifica-
tion and enumeration of specific and known targets, and (2) the detection
of any changes or new activity in his sector that might be of interest
to the analyst. The image interpreter must accurately perform these two
principal tasks under the pressure of a very demanding time schedule.
It is anticipated that the possible future use of color imagery will not
significantly modify the nature or content of these two principal require-
ments. It is expected that color imagery will require the image inter-
preter to name or, in some other way, read out the colors of certain
targets for which he is responsible and to search for particular colors
that may be of value to the analyst. At the present time, however, the
analysts and other users of the information have specified neither what
kind of color-related information they need nor what form would be most
useful.
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4.1.2 Collateral Researchers
The primary function of the collateral researchers at the Center
is clerical. In addition to some editing responsibilities, the collateral
researchers obtain, distribute, and collect the forms used for compiling
the information being reported by the image interpreters. Except for the
addition of some new color-related terms or new color-reporting forms, it
is anticipated that the use of color imagery would not significantly alter
the clerical functions of the collateral researcher. Nevertheless, the
possible use of color imagery would require the collateral researchers to
search, collect, and catalog color-related information about the targets
or other objects located in their geographical sector of responsibility.
This means that they would need to understand the color vocabulary used
by others.
The editors at the Center check and correct the format and style
of the written material that is submitted for publication by members of
the staff. The major portion of an editor's time is spent in editing the
material submitted by the image interpreters. Because of the nature of the
first-phase reports, it is anticipated that any possible future use of color
photography will not significantly modify this part of the editor's job.
Nevertheless, the possible use of color imagery could lead to the writing of
second-and third-phase reports that contain a considerable amount of
color-related information. To edit this type of material, some of the
editors would have to acquire an understanding of the color vocabulary
used by the Center.
The model makers at the Center design and build detailed scale
models of the various targets that have appeared in the imagery. These
models are used as visual aids for presentations such as formal briefings
and to aid the interpreters in their study of particular ground objects
or targets. It is interesting to note that the model makers are already
building colored models even though most of the data they use for their
construction has been acquired from black and white imagery. The major
problem that might be experienced by the model makers if color imagery
were to be used would be in making the colors of the model duplicate what
the interpreter sees in his viewer. This problem would be caused by the
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difference in the texture of the color material rather than by differences
in the hue, saturation, and lightness of the two colors. It is clear,
however, that, to enable the model makers to duplicate the actual color of
the target, accurate color information will be required through the use of
a precise visual color reference system.
The librarians at the Center perform the same job tasks (e.g.,
cataloguing, indexing, etc.) that are done by the librarians in any
technical library. The use of color imagery should neither significantly
modify nor add to the tasks currently performed. However, it might be
necessary for the librarians to increase the scope of their present in-
dexing methods so that the catalogue cards would include some comments or
notations for those library materials that contained color-related in-
formation. In general, it is believed the librarians will need a very
simple color vocabulary that would contain limited numbers of color-related
words and terms.
4.1.6 Scientists and Engineers
The scientists and engineers at the Center direct the research
and development of concepts, techniques, and equipment that will aid in
the exploitation of imagery. The use of color imagery has had and will
continue to have a significant impact on the tasks performed by these
engineers and scientists. They will have to be fully aware of all aspects
of color and its relationship to the exploitation of color imagery.
Furthermore, it is expected that the use of color imagery will necessitate
these people being aware of the job-related color needs of others at the
Center so that they can provide advice and assistance to these individuals.
The scientists and engineers will need a vocabulary that is both unlimited
and accurate.
The artists and illustrators at the Center produce drawings,
sketches, and other types of visual presentation materials at the request
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of various members of the staff. These visual materials that are prepared
are used for both oral and written reports. Most of these drawings are
intended to aid in the explanation of a concept rather than to be exact
renditions of actual objects. At the present time the artists and illus-
trators select colors only for visual emphasis and aesthetic qualities.
However, it is anticipated that the use of color imagery will not signifi-
cantly modify the color-related aspects of their jobs. If exact rendition
is ever needed, the artists and illustrators will.need to understand the
vocabulary of the requester who, in turn, will need to furnish a color-
reference sample.
4.1.8 Photographic Technicians
The term "photographic technician" describes all those individuals
at the Center who are involved in the making of continuous tone
prints and transparencies, which are used for briefing boards and reports,
and halftone transparencies, which are used by the printing shop. It is
anticipated that the use of color photography will increase the color-re-
lated job problems for this group at the Center. For example, the process-
ing of color films and papers takes considerably more time and is more
complex than the processing of silver halide-based black and white films
and papers. In most of these cases, the specialized photographic vocabu-
lary of the technician will be adequate. Nevertheless, a problem the
photographic technician might have is clearly communicating with the
individual who initiates the request for color prints and transparencies.
If the image interpreter wants a print that emphasizes the red color in
the picture, then he and the photographic technician must clearly agree
on how much emphasis the reds are to receive and how large a shift in the
overall color balance of the print is to be tolerated in achieving the
requested emphasis. In this case, some type of a visual color reference
system will be required.
As might be expected by their title, the printers are responsible
for the printing, collating, trimming, and binding of reports published
by the Center. The future use of color photography at the Center may
have a major impact on the job-related color needs of the printers. Pre-
viously, the color printing that was done at the Center was two and three-
color printing with flat inks rather than four-color printing that uses
process inks to create a full gamut of colors. As a result of the recent
introduction of four-color printing at the Center, some of the printers
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in the print shop will need to understand the principles of the subtractive
color process, as well as certain color-related printing problems such as
ink trapping and dot gain. In those situations where accurate color re-
production is required, the printer will need to use color-reference samples
to visually check the quality of the reproductions.
4.1.10 Photogrammetrists C
The primary function of the photogrammetrists at the Center is the
accurate and precise mensuration of the images of targets and objects whose
spatial dimensions are of interest and of use to the image interpreters
and analysts. The use of color imagery is expected to have more of an
effect on how the photogrammetrists perform their various mensuration tasks
rather than the tasks themselves. For example, the specific color of the
image of an object or target whose spatial dimensions are to be determined
should not create a major communication problem between the photogrammetrists
and the image interpreters because the present method could be used which
requires the image interpreter to set the cross-hairs of the comparator on
a target and say "That's the target I want measured". The real color-related
job needs of the photogrammetrists are anticipated to be related to the
development of techniques for the mensuration of color imagery. In this
latter situation, they will need to understand concepts such as hue, satura-
tion, and lightness, and color-related terms such as cyan, magenta, and
yellow. Of importance to the photogrammetrist will be the visual problems
(e.g., Mach bands and simultaneous color contrast) that are related to the
perception and mensuration of color images.
4.1.11 Managers
The job-related color needs of the individuals in management
.positions are as varied as the activities of the Center. The use of color
imagery by the Center could cause a significant modification in the activi-
ties of some managers. In most cases, however, the needs of the individual
managers at the Section or Branch level will correspond to the color vocabu-
lary needs of the individuals who work in these organizational units. For
example, the Branch Chief who manages scientists and engineers who are
directing the research and development of new image exploitation equipment
will need a fairly comprehensive understanding of the psychophysical
nature of color and the vocabulary used by his associates. The job-related
color needs of managers above the Branch level cannot be so easily identi-
fied. At this time, it is anticipated that they will need to know only
the general concepts of color and the terminology used to describe these
concepts.
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5.0 DISCUSSION AND INITIAL EVALUATION OF VARIOUS COLOR SYSTEMS
The third aspect of this investigation was a study of some of the
existing color systems that might be used as the basis for the recommended
color vocabulary. The purpose of all color systems is to designate the
differences between colors in terms of a standardized set of words or
numbers or some combination of these words and numbers. Some of the color
systems that were investigated had been developed for very specialized
purposes, whereas some of the color systems could be applied to a variety of
color-naming or color-designing problems. Each of the selected systems was
reviewed and studied to determine its applicability to the anticipated
future color needs of the Center. To cast each system into its proper
perspective, four major points were investigated for each major color system.
(1) The basic concept of the system
(2) The way the system might be applied
(3) The advantages of the system in terms of the anticipated
needs
(4) The disadvantages of the system in terms of the anticipated
needs.
5.1 COLOR SYSTEMS
5.1.1 The Munsell Color System
5.1.1.1 The Concept and Description of the Munsell Color System
The Munsell Color System is an orderly arrangement of a series
of colored plaques or chips whose colors were selected so that perceptually
there are nearly equal intervals between adjacent chips. In keeping with
the tridimensional nature of color, the Munsell chips are usually arranged
in the cylindrical pattern shown in Figure 5.1. In this color-order system,
the term 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 capital
letters (R, B, and G). 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 is designated by the term Value. A Munsell Value of 0 on
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the vertical axis in Figure 5.1 represents a black whereas a Munsell Value
of 10 at the top of the same axis represents white. Various shades of
gray and 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 of the color or
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 2YR
and value 6 varies from a light brownish-gray (a Chroma of 1) to a vivid
orange (a Chroma of 14).
5.1.1.2 The Application of the Munsell Color System
The Munsell designation for the color of an object in a back-
lighted color transparency would be determined by an image. interpreter
visually selecting the frontlighted Munsell chip that was the nearest
visual match to the color of the object. For example, the Munsell chip
that might be the nearest visual match for the color of a light blue
car would have the Munsell designation of 9B 6/8 (i.e., Hue Value/Chroma).
If the Munsell color system were used, it is anticipated that some type
of special eye piece or viewing equipment would be used so that the image
interpreter could view simultaneously the backlighted color transparency
and the frontlighted Munsell chips.
5.1.1.3 The Advantages of the Munsell Color System
The principal advantage of the Munsell color system is that it is
based on the visual rather than the physical aspects of color and color
perception. The dimensions of the Munsell color system, Hue, Chroma, and
Value, have direct correlations to the perceptual aspects of color, hue,
saturation, and lightness. It is anticipated that the staff would have
little difficulty in learning to understand and to use the concepts em-
bodied in this system. Another advantage of this system is that the
designation for a color can be readily transformed to the corresponding
CIE numerical designation for the color. This is an advantage because
the CIE system is based on the physical aspects of color and color per-
ception which are the spectral distribution of light sources and the
spectral reflectance or transmittance of a sample.
5.1.1.4 The Disadvantages of the Munsell Color System
A disadvantage of the Munsell Color System in its present form
is that the observer is required to make a visual color match between a
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Q, W"
B = Blue
Y = Yellow
R = Red
G = Green
yG = yellow-green
LIGHT BLUE
9B 6/8
Hue Value/Chroma
0 (Black)
FIGURE 5.1 THE CONCEPT OF THE MUNSELL COLOR SYSTEM
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frontlighted Munsell color chip and a backlighted dye image. The viewing
conditions must be controlled carefully and the color-matching procedures
must be specified clearly if the color-matching procedure is to produce
accurate and precise results on a day-to-day and an observer-to-observer
basis. Another disadvantage of the Munsell color system is that it has
a limited color gamut. Although the color coordinates for the colors of
both natural and cultural objects are contained within the Munsell system,
the theoretical gamut of an acquisition material such as SO-242 or SO-255
is much larger than that. of the Munsell chips. Thus, it would be quite
possible to record on the film colors whose chromaticity coordinates were
outside the Munsell system. Both of the disadvantages listed above could
be minimized if not eliminated by using a set of dye-colored transparent
Munsell chips whose gamut could equal or exceed that of the acquisition
material. However, dye-colored transparencies may shift in color with age.
(Judd and Wyszecki, 1963; Wyszecki and Stiles, 1967; Evans, 1948; Billmeyer
and Saltzman, 1966; Newhall, Nickerson, and Judd, 1943)
5.1.2.1 The Concept and Description of the CIE Color System
The CIE (Commission Internationale de 1'Eclairage) color system
is based on the physical aspects of light and color perception. This
system has found widespread use in the scientific and technical community.
Furthermore, the CIE system makes use of the spectral reflectance or
transmittance of colored materials. These properties of colorants (i.e.,
dyes and pigments) are closely related to their physical structure, a
subject of much interest to the color scientist.
It was recognized, possibly as early as Newton's time, that. most
colors projected onto a white screen could be visually matched by pro-
jecting varying amounts of red, blue, and green light from three other
projectors onto a common area of the same screen. As more experiments
were performed, it was discovered that individual observers who had
normal color vision required approximately the same amounts of red, blue,
and green light to achieve a match. To standardize color-matching pro-
cedures and to help the people who were communicating with each other about
color, a group of scientists met on behalf of the CIE and examined the
color-matching data that had been collected. All of these color-matching
data were statistically adjusted and then used to define a new set of
color-matching functions for the standard observer. These color-matching
functions (x, y, z) are shown in Figure 5.2.
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T-spectral transmission of sample
I E-spectral distribution of light
source
x, y, z-CIE color matching
functions
X,Y,Z-CIE tristimulus values
x v 9-CTF chromaticit
coordinates
y
O
Excitation purity = a
a+b
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In addition to specifying the color-matching functions for the
standard observer, the scientists also defined the spectral distributions
for a set of standard light sources. These definitions are important be-
cause the apparent color of a sample changes as the spectral distribution
of the light illuminating the sample changes. The other factor that de-
termines the color of an object is its spectral transmittance or reflect-
ance. Thus, the CIE designation for a color can be calculated by combining
the color-matching properties of the standard observer, the spectral dis-
tribution of the standard source, and either the spectral transmittance
or the reflectance of the object.
The first calculation to be performed in determining the CIE
designation of an object is to form the product of T, the spectral trans-
mittance (or R, the spectral reflectance) of the object and E, the spectral
distribution of the standard source being used. A pictorial demonstration
of the results of this operation being performed for a transparent object
is shown at the top of Figure 5.2. -A new product is then formed by multi-
plying the initial result TE times x, y, and z, the color-matching functions.
The-curves representing the results of forming these three new products
(TEx, TEy, TEz) are shown at the end of the dashed line in Figure 5.2. The
area enclosed between the curved lines and the horizontal axis is the
quantity of interest in these three graphs and it is calculated by using
standard numerical integration techniques. The areas under these three
curves are proportional to the CIE tristimulus values that are denoted by
the capital letters X, Y, and Z and are used in the formulas listed at the
bottom of Figure 5.2 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 coordinates - by convention, x and y - on the CIE diagram shown
at the bottom right of Figure 5.2. The third dimension of the CIE color
space is represented by the tristimulus value Y and is called the lightness
value of the color. There are two other terms used in the CIE system. The
dominant wavelength (Ad) 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 a line formed by 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 (Pe) 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 being used. The CIE color system is based on the chara-
cteristics of the standard observer, a given light source, and the reflec-
tance or transmittance of objects being measured. However, in some cases,
the numerical CIE designation can be related to the visually perceived
aspects of color (hue, saturation, and lightness) by using the terms such
as lightness, dominant wavelength, and excitation purity.
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5.1.2.2 The Application of the CIE Color System to Color Imagery
There are two methods that could be used by the Center to deter-
mine the CIE chromaticity coordinates (x, y), lightness value (Y), exci-
tation purity (p ),and the dominant wavelength (a ) for the colors of d targets in the imagery. The simplest, but least accurate, method would
be to use a tristimulus colorimeter whose readings would be proportional
to the CIE tristimulus values (X, Y, Z). The chromaticity coordinates
(x, y) for the colors of objects that were measured with a tristimulus
colorimeter could be calculated by several methods. The complexity of
the methods used to calculate the chromaticity coordinates could range
,from a simple manual method to a completely automated and computer-
assisted method of calculation.
The second method that could be used to assist in determining the
CIE color designations (x, y, Y, pe, ad) would require that the optical
transmission of the target or area of interest be measured at many wave-
lengths throughout the visible spectrum. These spectral transmittance
values could be measured by having the image interpreter or photoscientist
use some type of micro-spectrophotometer. As explained in Section 5.1.2.1,
these values for the spectral transmittance must be combined with the ap-
propriate CIE color-matching functions and spectral distribution of a CIE
standard source before the tristimulus values (x, y, z) can be calculated.
These numerical calculations and manipulations are so tedious that
some type of automated data reduction and computation method would have to
be used if the CIE method were used.
5.1.2.3 The Advantages of the CIE Color System
The principal advantage of the CIE system is that it is based on
a standardized observer and on the physical aspects of color and color
perception. The use of the color-matching properties of a standardized
observer means the CIE designations are independent of the color-matching
capabilities of the individual making the color determinations or measure-
ments. Because the CIE designations are determined by using the results
of calculations for which the values of the spectral transmittance of
filters and the spectral distribution of sources are used, the system can
be used to predict the magnitude and direction of color shifts resulting
from variations in the optical properties of the colored sample or light
source.
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Another advantage of the system is that the color gamut of SO-242
lies within the boundaries of the CIE chromaticity diagram. Thus, the
chromaticity coordinates can be calculated and plotted for any color that
can be reproduced by SO-242 or similar acquisition materials.
Another advantage of the CIE system is that is is continuous.
For example, in color imagery, such as might be acquired with SO-242, the
color of the water in a swimming pool which has a. sloping bottom changes
gradually from a very desaturated light blue to a moderately saturated
blue or blue-green. This gradual and continuous gradation of, the color
of water with either depth or temperature is evident in imagery that
contains targets such as beaches and large industrial cooling ponds. By
using the CIE system, the image interpreter or photoscientist could
specify a unique set of chromaticity coordinates for the colors of objects
at any point in a given frame.
On the other hand, the CIE system can be used to determine an area
weighted or an averaged color for such things as stockpiled materials and
field crops.* As the wind blows across a field of grass, the leaves of grass
bend back and forth so that the sunlight is reflected from them at different
angles; thus, the color of the field changes. Because colored imagery
represents the colors of the target at a given instant of time, the color
of the crop at one end of the field might be different from the color of
the same crop at the middle or other end of the field. Similarly, the
color of stockpiled materials such as sand or gravel could vary because
the moisture content might be different at various points. To calculate
an area-weighted or an averaged color, the light from the entire area of
interest could be collected and optically mixed or optically integrated
before the light entered a device to determine the spectral transmittance.
The capability of calculating an area-averaged color would be important
in some cases because the development of a catalogue of color-related target
signatures could be based on an average of these area-weighted values for
the colors of objects that are acquired on a mission-to-mission basis.
5.1.2.4 The Disadvantages of the CIE Color System
The main disadvantage of the CIE system is that it requires the
image interpreter or photoscientist to use some type of equipment to
* Although techniques for determining an area-weighted or area-averaged
color could be developed for all the color systems discussed in this
report, such an area-averaging feature is part of both the CIE and
Densitometric Munsell systems and is, therefore, considered to be a
definite advantage of these two color systems.
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measure the optical properties of the area of the image of interest. In
general, such measurements are both time consuming and difficult to make
with a high degree of accuracy. Assuming accurate and precise spectral
transmittance data can be collected in a few minutes, the image interpreter
would still be required to perform a series of calculations before the
chromaticity coordinates for the color of the object can be determined.
Because of the tedious nature of these calculations, some type of auto-
mated data-handling capability would be required. Thus, it would be
costly in terms of both time and money if every image interpreter were
equipped with his own "black box" that read out the chromaticity coordi-
nates (x, y) and lightness value (Y) for colors of objects which he was
observing through a viewfinder.
Another disadvantage of the CIE color system is that it is dif-
ficult to relate chromaticity coordinates, lightness value, excitation
purity, and dominant wavelength to the visual perception of color. For
example, x = 0.490, y = 0.301, Y = 36%, pe = 46%, and Xd = 640 nm are not
quickly recognized by most people as being a possible color for a red barn.
Thus, there is a considerable gap between the CIE designation for a color
and common understanding. This communication gap could cause a considerable
problem in trying to establish some type of ground truth information by
reports based on strictly visual observation of the target of interest.
(Judd and Wyszecki, 1963; Wyszecki and Stiles, 1967; Billmeyer and Saltzman,
1967; Judd, 1970)
5.1.3 ISCC-NBS Color System
5.1.3.1 The Concept and Description of the ISCC-NBS Color System
*
The ISCC-NBS Color System was initially designed to aid in de-
termining and specifying the colors of drugs and chemicals. In recent
years, it has found a much wider application in many areas of industry
and science. Ths ISCC-NBS system is essentially the result of applying
a color-naming scheme to the Munsell system. As previously discussed,
Hue, Value, and Chroma are the three dimensions of the Munsell color space,
and they are arranged so that they form a cylindrically shaped color solid.
All colors that have a similar Hue, Value, and Chroma will be contained in
a small cell or volume within this solid. The concept of the ISCC-NBS
* ISCC-NBS - Inter-Society Color Council - National Bureau of Standards
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system is that all colors whose Munsell coordinates fall within this cell
will be called 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 5.3.
The modifiers to be used with these Hue names were selected to denote the
relative Chroma and Value of the colors contained within a given cell.
Examples of these Hue Modifiers are shown in Figure 5.4 for a purple Hue.
5.1.3.2 The Application of the ISCC-NBS Color System to Color Imagery
The ISCC-NBS name for the color of an object in a backlighted
color transparency would be determined by the image interpreter visually
selecting the frontlighted ISCC-NBS chip whose color was the nearest
visual match to the color of the object. For example, the ISCC-NBS chip
that visually might be the nearest match for the color of a military
vehicle might be dark grayish-olive. If the ISCC-NBS system were used,
some type of special eyepieces or viewing instruments would be needed so
that the image interpreter or photoscientist could view the backlighted
imagery and the frontlighted ISCC-NBS chips simultaneously.
5.1.3.3 The Advantages of the ISCC-NBS Color System
The principal advantage of the ISCC-NBS Color System is that it
is a standardized color designation system which uses words rather than
numbers or letters to designate color. Further, these color descriptors
adequately communicate the visual appearance of a color in terms of a
standardized color vocabulary. For this purpose, the ISCC-NBS system is
the best color vocabulary that has been developed to date. Also, the
ISCC-NBS color names are related to a set of standardized samples that have
unique Munsell and CIE designations and the system appears to be easy to
understand and to apply.
5.1.3.4 The Disadvantages of the ISCC-NBS Color System
There are several disadvantages to the ISCC-NBS Color System.
As would be expected for any color system that uses painted chips, the
ISCC-NBS'system has a limited gamut of colors. Nevertheless, as with the
Munsell.color system, the ISCC-NBS color gamut is large enough to enclose
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Red
R
Purple
P
Reddish orange
rO
Reddish purple
rP
Orange
0
Purplish red
pR
Orange-yellow
OY
Purplish pink.
pPk
Yellow
Y
Pink
Pk
Greenish yellow
gY
Yellowish pink
yl'k
Yellow-green
YG
Brownish pink
brPk
Yellowish green
yG
Brownish orange
brO
Green
G
Reddish brown
rBr
Bluish green
bG
Brown
Br
Greenish blue
gB
Yellowish brown
yBr
Blue
B
Olive-brown
OlBr
Purplish blue
pB
Olive
01
Violet
V
Olive-green
01G
FIGURE 5.3 THE ISCC-NBS HUE
MUNSELL VALUE OF
Kelly, 1955)
NAMES AND ABBREVIATIONS FOR A CONSTANT
SIX (Judd and Wyszecki, 1963; Judd and
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FIGURE 5.4 THE ISCC-NBS MODIFIERS FOR A PURPLE HUE
(Judd and Wyszecki, 1963)
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most of the colors that might be acquired on the imagery used by the
Center. Another disadvantage of the ISCC-NBS color system is that it is
a discrete rather than a continuous color system.
(Judd and Wyszecki, 1963; Judd and Kelly, 1955)
5.1.4 Lovibond Color System
5.1.4.1 The Concept and Description of the Lovibond Color System
The Lovibond color system is a color-specification system based
on a set of glass filters called Lovibond glasses. The various glasses
are made with a thin layer of colored glass flashed onto a clear glass
substrate. The red (R), blue (B), and yellow (Y) glasses* used in the
Lovibond filters are made by adding gold, cobalt, and chromium, respective-
ly, to the glass during the manufacturing process. Although these glasses
are calibrated in arbitrary units, there is a definite relationship between
glasses of the same or different colors. For example, a 6Y designation
indicates that this particular Lovibond glass has the same spectral trans-
mittance as six lY Lovibond glasses in series, and it might be used to desig-
nate a yellow-appearing Lovibond glass that had a certain thickness of a
chromium-enriched glass flashed on the clear support. Similarly, a Lovi-
bond glass designated as a 1R + 7B would have the same spectral trans-
mittance as a series of glasses composed of one 1R Lovibond glass and
seven 1B Lovibond 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. For
example, a combination of Lovibond glasses designated as lOR + 10B + 10Y
would approximate a 1.3 neutral density filter.
5.1.4.2 The Application of the Lovibond Color System to Color Imagery
The Lovibond designation for a color of interest would be
determined by having the image interpreter or photoscientist use some
* 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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modified form of a Lovibond colorimeter. One-half of the interpreter's
field of view in such a device would be filled with that image whose color
was to be determined and the other half of his field of view would be
filled with Lovibond glasses. He would change the Lovibond glasses in
the colorimeter until he found the combination whose color was the
closest visual match to the color of the target. For example, 20B +
30Y might be the Lovibond color designation that an image interpreter
would report as being the match for a given grassy area surrounding a
military complex.
5.1.4.3 The Advantages of the Lovibond Color System
The main advantage of the Lovibond system is that the glasses
are stable, standardized, and transparent. Because the color samples
are transparent, the same light source can be used to backlight both
the imagery and the Lovibond glasses. Although having both the imagery
and the standard color samples backlighted does not eliminate all the
problems in visual color matching, it should reduce some of the expected
problems. The Lovibond designations for the color can be transformed to
the CIE chromaticity coordinates and the lightness value. The gamut of
color created by various combinations of Lovibond glasses is approximately
the same size as the color gamut produced by various combinations of the
cyan, magenta, and yellow dyes that are used in SO-242. Another advantage
of the Lovibond system seems to be its simplicity and ease of application
to many practical color-matching problems.
5.1.4.4 The Disadvantages of the Lovibond Color System
One disadvantage of the Lovibond color system is that it is
difficult to relate the Lovibond designation to the visual perception
of color and such common color terms as light blue, dark red, and bright
green. This problem might cause considerable trouble if an attempt were
made to communicate color-related information by using this system.
Another disadvantage of the Lovibond color system is that it requires a
large number of glass filters and, therefore, would be rather cumbersome
to use. Because of these disadvantages, the Lovibond system is not
recommended as part of the color vocabulary.
(Judd, Chamberlin, and Haupt, 1962; Wyszecki and Stiles, 1967)
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5.1.5 Densitometric Munsell Color System
5.1.5.1 The Concept and Description of the Densitometric Munsell
Color System
The densitometric Munsell color-measurement system is based on
the Munsell color-order system and it is designed to be used for extract-
ing colorimetric information from prints and transparencies. However, in
this case, the Munsell Hue, Value, and Chroma of the color of an image
is determined by making measurements with densitometers and doing cal-
culations by using nomographs rather than visually matching the color of
a target with the color of a Munsell chip. The nomographs that are used
to assist in the calculations 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 can be determined by using
the same nomograph'provided that the transmission densitometer has the
same optical characteristic (e.g., acceptance angle, transmittance of
filters, etc.) as the reflection densitometer used in the construction of
the nomographs.
To determine the Munsell color designation of a target in an
aerial photograph, the red, blue, green, and visual reflection or trans-
mission densities of that target are measured. The difference between the
highest and lowest density reading and the difference between the inter-
mediate density reading and the lowest density reading are calculated by
the image interpreter. The ratio of these differences is also calculated.
The image interpreter determines the Munsell Hue, Value, and Chroma of the
image by using these calculated values and the nomographs that were
described above.
5.1.5.2 The Application of the Densitometric Munsell to Color Imagery
If the densitometric Munsell method of color designation were
used, the red, blue, green, and visual densities of the image would be
determined with a calibrated transmission densitometer. The necessary
calculations to determine the required density differences and the ratio
of these density differences could be done manually or automatically if
the data were fed into a small computer. If the calculations were done
manually, the interpreter would determine the Munsell Hue, Value, and
Chroma for the color of the target by using the appropriate nomographs.
If the calculations were done by a computer, the computer might be pro-
grammed to determine the Munsell Hue, Value, and Chroma of the color of
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the target. The difference between these two methods is the amount of time
spent between initial acquisition of the data and the determination of the
Munsell designation for the color of the target.
5.1.5.3 The Advantages of the Densitometric Munsell Color System
The principal advantage of the Densitometric Munsell method is
that it is a relatively simple and fast nonvisual procedure for determin-
ing the Munsell Hue, Value, and Chroma for the color of an image. Further-
more, these Munsell designations for a color can be transformed easily
to their corresponding CIE color designations. Another advantage of the
Densitometric Munsell system is that it can be used with either prints or
transparencies. In addition, if the target area is large enough to com-
pletely fill the aperture of the densitometer, then the Munsell designation
as determined by the Densitometric Munsell method is an area weighted or
averaged Munsell color designation.
5.1.5.4 The Disadvantages of the Densitometric Munsell Color System
The main disadvantage of the Densitometric Munsell Color System
is that there has not been sufficient verification of its applicability
to color transparencies. The nomographs which have been published to
date were constructed and verified by using opaque Munsell chips and color
prints. Thus, there must be a considerable amount of experimental work
completed before the Densitometric Munsell System could be used with color
transparencies.
Another disadvantage of the Densitometric Munsell Color System
is that the aperture openings on the conventional densitometer such as the
Macbeth TD-102 or RD-100 are at least 1 mm or larger in diameter. Small
aperture sizes are not used in these densitometers because the densito-
meters were designed to measure diffuse optical density rather than specu-
lar optical density of photographic materials. Most of the targets that
are expected to be of interest will have image sizes which are consider-
ably less than 1 mm in diameter. The use of such small apertures might
cause some very difficult calibration problems. Because of these disad-
vantages, the Densitometric Munsell is not recommended for the color
vocabulary.
(Gurley, Rib, and Miles 1968)
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5.1.6 DIN Color System
5.1.6.1 The Concept and Description of the DIN Color System
The DIN (Deutsches Industrie Normen) 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 which is the ratio of
the luminous reflectance of the color sample to the maximum luminous re-
flectance of all those colors that have the same chromaticity coordinates
as the sample. The D scale is equally spaced for both chromatic and
achromatic colors. The dominant wavelengths of the twenty-four different
Farbton used in the DIN system were selected so that the different colors
would be spaced in nearly equal steps. The lines radiating from the point
representing the CIE standard source C in Figure 5.5 are lines of constant
DIN-Farbton or constant T. The curves enclosing the point representing
the C source on the CIE diagram in Figure 5.5 represent levels of equal
visual saturation or constant, S.
5.1.6.2 The Application of the DIN Color System to Color Imagery
It is anticipated that the opaque DIN color samples could be used
in some type of visual colorimeter. The DIN color samples would appear,
one at a time, on one side of a bipartite field of!view while the image of
interest would appear on the other side of the field of view. The observer
would designate the color of the target as being the same as the color of
the DIN color sample that was the closest visual match to the color of the
image. Of course, the color designation of the target would be expressed as
so many units of T:S:D. For example, a yellow rose might be designated as
2:6:1 in the DIN color system.
5.1.6.3 The Advantages of the DIN Color System
An advantage of the DIN system is that it is a psychological
system which is based on the visual perception rather than the physical
aspects of light. Furthermore, the DIN designation for the color of an
object can be transformed to other color systems such as the Munsell and
CIE.
* Literally translated it means "darkness degree".
49
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Lines of constant T and S are
valid for all values of
DIN-Dunkelstufe, D.
I I I
0.4 0.6 0.8
FIGURE 5.5 THE LINES OF CONSTANT DIN-FARBTON AND DIN-SATTIGUNG
PLOTTED ON A 1931 CIE DIAGRAM
Line of constant DIN - Farbton, T= 22
Line of constant DIN - Sattigung, S = 12
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5.1.6.4 The Disadvantages of the DIN Color System
The very limited use of the DIN Color System outside Germany is
a definite disadvantage. It would be difficult to write equipment speci-
fications in terms of DIN color standards for contracts with American
manufacturers. Another disadvantage of the DIN system is that it is dif-
ficult to relate the numerical DIN designations for T, S, and D to the
colors they represent. Further, the DIN system is a discrete rather than
a continuous color designation system. Because of these disadvantages,
the DIN system is not recommended for the color vocabulary.
5.1.7 Ostwald Color System
5.1.7.1 The Concept and Description of the Ostwald Color System
The Ostwald Color System, which is very useful to artists and
decorators, is based on Ostwald's philosophical concept that colors could
be characterized by what he defined as their full color content, black
content and white content. How these concepts were applied by Ostwald
is illustrated in Figure 5.6. The spectral reflectance curve is for an
idealized colorant because such step-like changes in spectral reflectance
can only be approximated by an actual dye or pigment. The white content,
black content, and full-color content of such idealized colors were de-
fined so that their sum would equal unity (i.e., B+W+C = 1). For a color
defined in this manner, the standard Ostwald notation consists of a com-
bination of numbers and a word that specifies one of the twenty-four
hues used by Ostwald and two lower-case letters whose combination denotes
the white and black content of the color. The first letter in this
notation specifies the white content of the color and the second letter
specifies the black content of the color. Although the lower-case letters
in Figure 5.6 are the 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 a black content of 44.0
percent.
The idealized colors in the Ostwald system have some very inter-
esting colorimetric properties. For example, the colors in any one of
the diagonal columns have the same dominant wavelength but the colori-
metric purity increases as one moves 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
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cW=56.0
13=44.0
=35.0
-,B=65.0
W=22.0
black
FIGURE 5.6 THE OSTWALD COLOR SYSTEM
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increase as one moves from the bottom to the top. The hues are arranged
in a circular pattern as shown in the small diagram at the lower right of
Figure 5.6 and represent approximately equal intervals of visual perception.
5.1.7.2 The Application of the Ostwald Color System to Color Imagery
The Ostwald designation for the color of an object in a back-
lighted color transparency would be determined by visually selecting the
frontlighted opaque Ostwald color chip that was the nearest visual match
to the color of the object. If this system were to be used, some type of
special viewing equipment would be necessary so that the image interpreters
could view simultaneously the backlighted color transparency and the
.frontlighted opaque Ostwald chip.
5.1.7.3 The Advantages of the Ostwald Color System
An advantage of the Ostwald Color System is that the colors in
any diagonal series such as aa, ca, ..., pa or ii, ig, ..., ia, increase
in excitation purity (Pe) while maintaining a constant dominant wavelength.
Similarly, those colors in a vertical series such as pn, nl, ..., ca
represent a series of colors which have a constant value for excitation
purity but increasing values of lightness. These are advantages because
they represent the way most individuals visualize colors.
5.1.7.4 The Disadvantages of the Ostwald Color System
The principal disadvantage of the Ostwald Color System is that
real colorants do not behave in the manner predicted by Ostwald. Further,
the chips must be frontlighted which is a definite disadvantage. Also, it
is difficult to visualize the color represented by the Ostwald notations
for the various colors. Because of the absence of any unique advantages,
the Ostwald Color System is not recommended for the color vocabulary.
(Evans, 1948; Evans, Hanson, and Brewer, 1953)
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5.1.8 NuHue, Plochere, Ridgway, Maerz & Paul, Villalobos, Textile Color
Card Association, and Methuin
5.1.8.1 The Concept and Description of the NuHue, Plochere, Ridgway,
Maerz & Paul, Villalobos, Textile Color Card Association, and
Methuin Color System
All of the color-naming systems listed in this title consist of
an orderly arrangement of colored plaques or chips. These color systems
were designed for use by a specific industry or profession. For example,
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 paints.
These systems are quite 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. The
ISCC-NBS color "light blue" is "Diana", "Good Omen", "King's Blue", and
"Forget-Me-Not" by Maerz and Paul, Plochere, Ridgway, and the Textile Card
Association, respectively. In some of these systems, the color chips or
samples were made by using paints whose composition was unknown or cannot
be duplicated.
5.1.8.2 The Application of the NuHue, Plochere, Ridgway, Maerz & Paul,
Villalobos, Textile Color Card Association, and Methuin Color
System to Color Imagery
The NuHue or similar designations for the color of an image in a
backlighted color transparency would be determined by visually selecting
the frontlighted opaque color chip whose color most closely matched the
color of the image. If the NuHue or similar system were used, some type
of special viewing equipment would have to be used so that the image inter-
preter could simultaneously view the backlighted images and the frontlighted
color chips.
5.1.8.3 The Advantages of the NuHue, Plochere, Ridgway, Maerz & Paul,
Villalobos, Textile Color Card Association, and Methuin Color
System to Color Imagery
The principal advantage of these color systems is that they
designate colors by names which are somewhat descriptive of the color.
This would be a very definite advantage in trying to communicate color-
related information in a written or oral form.
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5.1.8.4 The Disadvantages of the NuHue, Plochere, Ridgway, Maerz & Paul,
Villalobos, Textile Color Card Association, and Methuin Color
Systems
The principal disadvantage of these color systems is that, in many
cases, they lack any plan or design in the selection of the colors they
have used. When these color systems were developed, there was no attempt
made to select colors or. to arrange them in any manner that correlated
to either the physical or psychological aspects of color. Furthermore,
most of the systems lack adequate standards so that it is very difficult
to reproduce the color samples accurately. Another disadvantage in using
such a pigmented sample is that they provide only a very limited gamut
of colors. Because of these disadvantages, these color systems are not
recommended for the color vocabulary.
(Evans, 1948; Wyszecki and Stiles, 1967; Judd and Wyszecki, 1963)
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6.0 CONCLUSIONS AND THE RECOMMENDED COLOR VOCABULARY
6.1 THE CONCLUSIONS OF THE REVIEW OF THE PROBLEMS RELATED TO THE
DEVELOPMENT OF A COLOR VOCABULARY FOR THE CENTER
The four major problem areas related to the development of a color
vocabulary have been discussed in Sections 2.0, 3.0, 4.0, and 5.0. These
four major areas are (1) the visual problems related to the interpretation
of color imagery, (2) the photographic problems related to the interpreta-
tion of color imagery, (3) the job-related color needs of the individuals,
and (4) the applicability of various color systems to the problem of
identifying, reporting, and catalogueing the colors of images. In each
instance, conclusions refer specifically to the color-related problems at
the Center.
The visual problems that are related to the interpretation of
small-scale, high-quality color imagery were discussed in Section 2.0 of
this report. From the experimental results presented in these discussions,
it is evident that under well-controlled viewing conditions, the average
color-normal individual has a tremendous capacity to accurately and reli-
ably discriminate differences,i.e., by comparative judgment between the
colors of two structure-free fields. The accuracy and precision of these
color-discrimination judgments that are made by the average color-normal
observer will deteriorate rapidly if the viewing conditions are not well
controlled and maintained. Nevertheless, even with poorly controlled
viewing conditions, the accuracy and reliability of his comparative judg-
ments will probably be greater than his color memory or any other absolute
color judgment. However, his color memory can be improved by practice and
frequent practice of the exercises.. On the basis of this evidence, it is
concluded that a color vocabulary which consists of more than fifteen to
twenty different colors must be used with some type of a visual color-
reference system. Furthermore, the viewing conditions for using this
visual color-reference system must, in part, be clearly specified, under-
stood, and used. In addition, the color vocabulary must be able to
designate a large number of colors because of the color-discrimination
ability of the typical observer.
Some of the photographic problems of small-scale color imagery
which were considered to be relevant to the color vocabulary were dis-
cussed in Section 3.0. Images of targets expected to be of interest to the
Center would generally have an angular size of less than two degrees when
viewed at the maximum useable magnification (60x). Fields of view whose
angular sizes are the order of one-to-two degrees or larger are considered
necessary for accurate and reliable color matching or color discrimination.
Therefore, it is concluded that because of the small angular size of the
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targets of interest, it will be difficult but not impossible to use a
visual matching technique to reliably determine the colors of an image.
The color fidelity of imagery acquired by using acquisition films
such as S0-242 or S0-255 was also discussed in Section 3.0. It was stated
that the color fidelity or color-rendering properties of color reversal
films such as S0-255 or S0-242 were degraded because the photochemist also
had to consider factors such as resolution, dye stability, and cost in his
selection of the sensitizers and the colorants. It was demonstrated in
Section 3.1 that noticeable color shifts or color variations can result
from small changes or variations in exposure. Similarly, color shifts
of the same magnitude can be expected for variations in other acquisition
factors, such as sun angle and atmospheric conditions over the target. It
is apparent from these results that, at best, the image colors will be only
close approximations to the actual or "ground-truth" colors of these ob-
jects. It is also apparent that the image colors of an object will vary
on a mission-to-mission basis if not on a frame-to-frame basis. Thus, any
accurate measurement of the image color will be only. the best approximation
to the actual color. It is concluded that any color vocabulary that might
be used by the Center must be capable of accounting in some way for these
variations in the image color of a target if the actual color is to be
determined. Furthermore, the ground-truth color of a target can not be
determined solely from the information that can be extracted from the
imagery because color photography is an integrating process. To determine
the actual color of an object, the image interpreter or photo-scientist
must use some type of an acquisition model which includes and accounts for
such variables as sun angle and atmospheric effects. If such a model or
correction formula were not available, precise measurements would not be
of value and a less accurate measurement system would suffice. Hence, one
of the outputs of the color vocabulary should be color-related data that
can be used as an input to an acquisition model which would be used to
determine the actual color of the object.
In order to account for the color communication needs of the
personnel described previously, it is concluded that a tri-dimensional
or three-level color vocabulary is needed. One level of this color
vocabulary would need to be a color-measurement system that was capable
of designating a large number of colors and the output of which would
be a notation indicating the precise value of the color. This level of
the color vocabulary would be used for exact and precise color communication.
Another level of this color vocabulary would be needed for the verbal and
visual communication of the colors. Such a system must contain a set of
reference colors. Finally, a simple set of color names could be used when
accurate and precise color identification is not needed or could not be
obtained. These color names would simply communicate the general color,
e.g., blue, blue-green, yellow, etc..
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Finally, from the study of the color system, it was concluded
that the Munsell, CIE, and ISCC-NBS color systems were the best of the
available color systems for the color vocabulary. The CIE color system
was selected because it is (1) precise, (2) continuous, and (3) related
to the physical aspects of color. The Munsell color system was selected
because it is a visual color reference system that contains a large number
of color samples and is related to the visual and psychological aspects of
color. The ISCC-NBS color system was selected because it uses a set of
standardized color names, that are quite descriptive (e.g., vivid red) of
the colors they represent, and the color samples are related to the Munsell
system.
6.2 THE CONCEPT OF A MULTILEVEL COLOR VOCABULARY
A color vocabulary based on a single color system did not appear
to adequately satisfy the needs of the individuals at the Center and its
overall color-related mission requirements. However, many of the re-
quirements that have been placed on the color vocabulary could be satisfied
by a multilevel color vocabulary whose structure would be similar to, if not
the same as, the "universal color language" described by Kelly (1965). The
lowest level suggested by Kelly would consist of approximately fifteen
colors and neutrals that would be designated by their generic hue names
such as red, blue, green, ..., white, gray, and black. The complexity of
the color system and the number of colors would increase as the level of
the color system increased. Kelly has proposed that the ISCC-NBS system
be used for the middle level of the universal color language. The ISCC-NBS
color system has 267 colors which are described by both hue names and
modifiers such as "vivid red" and "very dark yellow-green". The upper
level of the universal language described by Kelly has the greatest accuracy
of identification and uses a system such as the CIE or Munsell. Thus, in
passing from the lowest to the highest level, both the accuracy of
color identification and the complexity of the system has been increased
greatly. The principal advantage of such a multilevel vocabulary is that
each level not only satisfies a particular set of color communication needs,
but also relates to those at all other levels. Also, the "color resolution"
or accuracy of color identification can be increased easily by simply moving
to the next higher level.
It is concluded that the level of the color vocabulary used by
the individuals at the Center is dependent upon the type of color-related
information the individual is trying to communicate rather than his specific
job requirement. For example, in some cases, merely creating the impression
of a color is sufficient; therefore, a set of simple color names is all
that is required. In those cases where a more precise impression of the
color must be communicated, the individuals would both visually and verbally
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communicate the color. Here the ISCC-NBS or Munsell color system which
contains color-reference samples would be used. Which of these is used
is dependent upon the accuracy required. Lastly, for those who want to
communicate the physical aspects of color, the CIE system would be
needed.
On the basis of all the preceding information, it is concluded
that the color-related needs of the Center and the job-related color
needs of the individuals can best be satisfied by a three-level color
vocabulary. The first level would consist of approximately twenty color
names such as red, blue, brown, ..., gray, and black and the lightness
descriptors light and dark. A reference set of color samples would be
included, but not for the purposes of matching. At this level, it is only
important that the generic hue name and general lightness value of the
.color be indicated.
The second level of the color vocabulary should consist of some
type of color reference samples that could be used in the visual com-
munication of color related information. Either the ISCC-NBS or the
Munsell color system could be used for this level of the color vocabulary.
Which of these two color systems is used is dependent upon the level of
precision that is needed for visual communication. The Munsell system
would be used for the precise visual communication of color-related in-
formation, such as would be needed in the accurate reproduction of color
imagery. The ISCC-NBS color-naming system would be used in those cases
where such precision was not needed.
The third level of a color vocabulary the Center could use is
the CIE system. The colors of the images would be designated in terms of
their CIE chromaticity coordinates (x, y), lightness value (Y), excitation
purity (p ), and dominant wavelength (Ad). This level of the vocabulary
would also need to account for the inaccuracies of the acquisition and
processing systems. Because of the complexity of the CIE system, it is
anticipated that the Center would need to develop a capability for solv-
ing color-related problems which would be similar to their present capabil-
ity for solving mensuration problems.
For general communication, everyone would use the first-
level vocabulary. The image interpreters might report out the image color
of targets (when precise requirements are not needed) by using such terms
as light brown, blue, dark green. The illustrators might be requested
to make a VUGRAPH that had red letters on a light yellow background.
The use of the second level of the color vocabulary (ISCC-NBS or Munsell
color system) would be used in those cases where the communication needs
to be more precise. For example, the ISCC-NBS system might be used to
report that in a given area all the tanks had been repainted a dark
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olive-green instead of dark grayish olive-green. This is analogous to
the situation where the image interpreter scales the length of a target
and calculates its longest dimension to be somewhere between 195 and 200
feet. Similarly, the second level would be used by an image interpreter
if he wanted the model maker to use light yellowish-brown paint instead
of a grayish yellow paint for painting the dead grass around a chemical
factory or industrial complex. In these cases, the color names would be
selected by grossly matching the color image to the ISCC-NBS color chips.
Since this is a gross match, complex equipment and standardized viewing
conditions would not be required.
If a more precise color identification were required at this
second level, the Munsell color system should be used. The individual
would probably have to take his imagery or prints to experts who would
determine the Munsell designation of the color under controlled and
standardized viewing conditions.
The third level of the color vocabulary would be used only.. in
those situations where it was necessary to very accurately determine the
color of a target. This is analogous to the case where the image inter-
preter realizes it is important to know whether the width of an antenna
is 10 feet or 10.125 feet. At this third level, the image interpreter
would take his imagery to those individuals or that group who could make
accurate color measurements and request that they determine the CIE
chromaticity coordinates and lightness values for that particular target.
The scientist and engineer would also use this third-level vocabulary
for scientific communication, designing experiments, and writing
specifications.
6.3 SELECTION OF THE FIRST LEVEL COLOR VOCABULARY
The color names for the first level color vocabulary were
selected in the following way:
(1) The visual spectrum was separated into its unique hue
names: red, orange, yellow, yellow-green, green, blue-
green, blue, violet, and purple*.
(2) Each spectral hue was conceptually varied in lightness
from light to dark to determine if unique and commonly
recognized color names could be used to represent the
lightness differences. This step resulted in addi
tional color names: pink, brown, and olive.
Although purple is not a spectral hue, it is considered a unique hue.
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(3)
To represent various brightness levels, the two modifiers
light and dark were added to the vocabulary.
(4) To represent the gray scale, the terms white, gray, and
black were chosen.
(5) The color names cyan (a blue-green) and magenta (a purple)
were added because of their frequent and consistent use
in color-reproduction and processing. However, these two
color names are not to be used for describing image colors.
These steps resulted in a vocabulary of two modifiers, light and dark, and
seventeen (17) names: pink, red, orange, brown, yellow, yellow-green,
olive, green, blue-green, blue, violet, purple, white, gray, black, cyan,
and magenta.
6.4 THE RECOMMENDED COLOR VOCABULARY
As a result of this study, it is recommended that the Center use
a trilevel color vocabulary. The first level of this vocabulary consists
of seventeen names and the modifiers light and dark. The seventeen
recommended names are pink, red, orange, brown, yellow, yellow-green,
olive, green, blue-green, blue, violet, purple, white, gray, black, cyan,
and magenta. Combinations of any two of these names such as red-brown
(except cyan and magenta) can be used in those few situations where the
basic names are not adequate. The names cyan and magenta are not to be
used for image colors. Samples of these colors (excluding white, gray, and
black) are included in the back of this report.
It should be emphasized that these seventeen color names are
recommended only as the starting point for the first level of color
vocabulary. If in use at the Center it is found that some of these names
are not used or that there is a need for some additional color names, then
it is recommended that such changes be made by the Center.
The second level of the vocabulary consists of both the Munsell
and ISCC-NBS color systems. The degree of precision needed in the visual
communication of color-related information determines which of these two
color systems is to be used. The ISCC-NBS color system is used when a
non-precise visual color reference is required for communication. This
system is implemented in normal working and viewing conditions, since the
widely separated color samples do not require the use of critical color
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matching. When a more precise visual color reference is required, the
Munsell system is used. All the Munsell color matches or designations
are made visually, under specified and well controlled viewing conditions
by well trained individuals. Ideally, transparent Munsell samples are
used in a split-field viewer. If, however, the dyes are too unstable to
make these transparencies practical and reliable, then the matte-finished
Munsell chips are used. To implement the use of the matte-finished chips,
a split-field viewer may be needed. The chips are placed in one-half of
the field of view and the film'in the other half. The lighting in each
'half of the viewer is adjusted so that both the film and the chip receive
equivalent illumination in terms of intensity and spectral distribution.
Apertures are used in both fields to reduce the influence of the colors
surrounding the target, while keeping the size of both fields of view the
same. Although this device is an aid to color matching, the texture
differences between the film and the matte chip may still cause perceptual
difficulties. However, there is evidence that. with practice and experience
one can adapt to these texture differences (Parry, et al., 1969 a,b).
The third level of the recommended color vocabulary is the CIE
color-designation system. To implement this third level of the recommended
color vocabulary it will be necessary to develop a color-correction model
to account for the effects of acquisition and processing on color fidelity.
If this model is not developed, then precise color measurements would not
be valid or needed. In addition, it is recommended that the Center develop
the capability for performing accurate reliable color measurements and
calculations by forming a colorimetric group.
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