Naval Submarine

NSMRL REPORT 1174

Medical Research Laboratory

FREQUENCY OF COLOR NAMES

FOR COLORS GENERATED ON A CRT

by

J. DiVita, D. F. Neri,

and M. J. Shim

Released by:

R.G. Walter, CAPT, DC, USN

Commanding Officer

Naval Submarine Medical Research Laboratory

Approved for public release; distribution unlimited

30 DECEMBER 1991
Frequency of color names

for colors generated on a CRT

by

J. DiVita

D. F. Neri,

and

M. J. Shim

Naval Submarine Medical Research Laboratory

NSMRLReport 1174

Naval Medical Research and Development Command

Research Work Unit 65856N M0100.001-5003

Approved by

R. G. Walter, CAPT, DC, USN

Commanding Officer

Approved for public release; distribution unlimited
SUMMARY PAGE

PROBLEM

To obtain color naming boundaries within the realizable color space of standard CRT displays.

FINDINGS

Color naming boundaries were constructed from the responses of 10 subjects to

210 equally spaced equiluminant stimuli for criteria of 50%, 75%, and 95%.

At the 95% criterion level, only green, blue, and purple regions were obtained.

When the criterion was dropped to 75%, yellow, orange, pink, and aqua

regions were added to the map.

APPLICATION

The results of this experiment provide the data base with which to compare alternative strategies for the application of colors to tactical CRT displays.

ADMINISTRATIVE INFORMATION

This work was accomplished under work unit 65856N M0100.001-5003, "Enhanced performance with visual sonar displays," approved for publication on

30 December 1991, and has been designated NSMRL Report Number 1174.

The views expressed in this article are those of the author and do not reflect

the official policy or position of the Department of the Navy, Department of

Defense, or the U. S. Government.

ii
ABSTRACT

Color naming frequency data were collected for 210 equiluminant colors. These

colors represent a sample of the color space realizable on a CRT screen. From these

data, color naming boundaries were constructed utilizing criteria of 50%, 75%, and

95%. The results of this experiment provide a data base with which to compare alternative strategies for the application of colors to CRT displays.

iii
Frequency of color names for colors generated on a CRT

INTRODUCTION

The application of color to tactical

CRT displays has as its goal the improvement of operator performance.

The improvement may result from the

careful use of color to (a) convey informa

tion about the status of a system or subsystem more quickly (e.g., warning or

status lights), (b) improve discrimination between different types of information (e.g., target and background), or (c)

group related information for faster association (e.g., target and associated alphanumeric data). Adding color

properly for these or other purposes requires the consideration of many issues.

One major issue concerns the number of

colors to use and what they should be.

The number of colors should be large

enough to make the addition of color enhancing while not so large as to make

discrimination between colors difficult.

In other words, for many applications

the colors should not only be easily discriminable but also easily identifiable.

The latter requirement implies that the

best sets of colors may be those in which

all members have reliably different

names.

Currently, display designers use the

International Commission on Illumination (CIE) color spaces to specify colors.

In the CIE 1976 color space, the linear

distance between two equiluminant

colors is a first approximation to their

perceptual difference (Robertson, 1977).

Thus the points on a circle, in this color

space, should all be equally distinguishable from the color represented by the

center of the circle, again to a first approximation. This characteristic is more

true of certain regions than others. Post

& Greene (1985) and Post & Calhoun

(1988) have argued that color-naming

boundaries should be taken into account

when selecting colors on CRT displays.

Post and Greene state that "The implicit

assumption of this research is that the

reliability of subjects' color-naming behavior is indicative of their ability to

recognize colors, and hence apprehend

color codes." However, is Post's assumption valid? This question can only be

answered by experiments that directly

compare subject color-naming behavior

to color discrimination and identification.

Color-naming boundaries may be

defined as contours in a color space

enclosing regions within which the application of a given color name exceeds a

criterion probability. These boundaries

pose an interesting problem when considered in the CIE 1976 color space.

Will a pair of colors that straddle a colornaming boundary be more discriminable than a widely-separated pair

falling within the same color naming

region? Or would the reverse be true?

This question may also be asked of color

identification. Given the importance of

color discrimination and color naming to

the application of color to tactical displays, the purpose of the present study

was to collect information that will

serve as a data base for future experiments concerning the effect of colornaming boundaries on color

discrimination and identification. In

1
the experiment to be described, colornaming boundaries were determined experimentally for a set of equiluminant

colors. These data will then be used to

evaluate the effectiveness of colornaming boundaries on color discrimination and identification tasks.

METHOD

Subjects

Ten color normal subjects, eight

female and two male, were paid for their

participation in the experiment. The

subjects' color vision was tested using

the Hardy-Rand-Rittler pseudoisochromatic plates.

Apparatus

A Vax 750, a Ramtek 9400/91

graphics display generator, and a Matsushita standard phosphor color monitor

were used togenerate the colors. Theaddressiblity of the monitor was 1280 by

1024 pixels (100 pixels per inch). All

color measurements were made with a

Photo Research Model 703A Fast Scanning Spectroradiometer. The CIE 1976

chromaticity coordinates (u',v') of the

phosphors were (.41,.52) for the red,

(.12,.56) for the green, and (.17,.18) for

the blue.

Stimuli

The coordinates for the red, green,

and blue CRT phosphors form the vertices of a triangle in 1976 CIE color

space. The colors producible by the display are then represented by the area of

this triangle. To select the color stimuli

to be used in this experiment a coordinate grid was first placed over the tri0.6

0.5

0.4

V 0.3

0.2-

0.2- CE W0 1976 UCS

4600 Diagram - 4500, 440 %

4200o 400nm

0 0 I ' I ' ' I

0 0.1 0.2 0.3 0.4 0.5 0.6

U

Fig. 1. The 210 stimuli used in the experiment are mapped into the 1976 C.I.E. color space.

2
angle of realizable colors. The grid consisted of points that were equidistant

from all adjacent points. In other words,

any three adjacent non-collinear points

form the comers of an equilateral triangle. There were 210 points that fell

within the area of the color triangle.

Points that fell on or outside the legs of

the triangle were excluded. Included

points then became the u',v' coordinates

for the 210 color stimuli shown in

Figure 1.

The CRT was characterized using

the procedure of Neri (1990) such that

it was possible to produce the 210 equally-spaced chromaticities. The stability

of the CRT was such that a computer program using the output of the characterization procedure could produce

colors with chromaticities accurate to

.01. The luminance of all stimuli was

2 10.0 c/in

80-

I0

Z

W

0

iri

0

a75-

70

65-

Procedure

The procedure follows closely that of

Post & Greene (1986) and Post & Calhoun (1988). Each of the 210 stimulus

colors was presented in isolation as a circular patch subtending a visual angle of

1 degree, against a flat black cardboard

background attached to the CRT screen.

The subjects were instructed to name

each of the colors presented. The ten

color names allowed as responses were

limited to: red, green, blue, aqua,

orange, yellow, pink, purple, gray, or

white. These particular color names

were selected since Post and Greene

(1985) showed in a similar experiment

that when subjects' naming responses

were not constrained, that 88% of the

responses were comprised of these ten

color names. Subjects made their

response by pressing a number on a key

pad. A chart, coding the 10 colors to

numbers, was always visible to the subI I I I I I I I I I I -I 1 2 3 4 5 6 7 8 9 10 11 12

BLOCKS OF TRIALS

Fig. 2. Average consistency across subjects between adjacent blocks of trials.

3
ject. After each response was entered,

the program informed the subject of the

color name he or she had ascribed to the

stimulus and asked the subject if this

was the correct name. If the subject

responded yes then a new color was

presented. If the subject responded no,

the program allowed the subject to

reenter the number that corresponded to

the color name. In this manner subjects

were given a chance to correct any mistakes that may have arisen from pressing the incorrect number.

A block of trials consisted of each of

the 210 colors being randomly presented

once. Subjects were tested on a total of

12 blocks of trials for a total of 2,520

responses per subject.

RESULTS

Figure 2 shows the percentage of

"same" responses for the same colors between successive blocks of trials,

averaged across the 10 subjects. That is,

between successive blocks of trials the

responses to each individual stimulus

were compared for all subjects and the

number of stimuli that were called by

the same name is given by a percent. Between blocks one and two, for example,

the subjects'consistency is about 69%.

It rises to 75% between blocks 2 and 3.

It stays above 75% after the second trial

except for an unexplained drop between

trials 4 and 5. Since the consistency of

response is fairly well established by the

third block of trials, the first two blocks

have been treated as practice trials.

Therefore, the results of the experiment

are based on the last 10 block of trials.

COLOR NAME BOUNDARIES FOR P > .95

GREEN

BLUE 0 PURPLE 0 

.25 .35

U,

Fig. 3. Color-naming boundaries for a modal response of 95% or greater.

4

V ,

.55

.45

.35

.25

.15

.05 .15 .45
COLOR NAME BOUNDARIES FOR P > .75

GREEN YELLOW

.45 AQUA3. . .

vI PINK .35

.25- PURPLE

.25

.15 BLUE

.05 .15 .25 .35 .45

UI

Fig. 4. Color-naming boundaries for a modal response of 75% or greater.

COLOR NAME BOUNDARIES FOR P > .50

GREEN

.45 AQUAa

4 PINK

V

235

. 5BLUE , •PURPLE

* [ -GRAY

.15 I i ' I 1 

Fig. 5. Color-naming boundaries for a modal response of 50% or greater.

5
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045--

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'35-

.25-

.15 I

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96 a ý97•0 .91 8 .57 8 .93 .60 .63 * .9l 3 .99 8 .73 8 .67 8 .36 0 6£7 8 .86 .96 ,86

.96 8 940 .64 0 .5. 1 . 2 .57 b8 0 .7 * .94 8 .35 75 * .96 • 900• 768u •710 620• .62 8 990 .64 0 .4•4 8

".82 6.63,88 0 .39 .54 .678. 0 .84 0 .51 8

* .71 0 .84 .468 • 1 40 .30 .57 0 .72 a .54 8 .58

.57 0 .:2 0 .54 . .42 8 .34 0 460 .52 0 .38 . .53 0

* 538 .57 T 528 43 ..33 .41 8 .49 8 .43

. .52 8 .4 8 .64.0 23 '53 8 628 .69 8 .5 ".77 8 .31 8 .49 8 .39 0 .54 0 .70 8 .83 8 .3 0 * .640•.608. 520•.940•.'780 650.16•,8

.750 .34 0 .:3. .2.0 9. .. .. 04 8 .1,.

* .6: 1 .59 _ 420 •.42 0 .80 8 .0 6 8 02

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T .74 0.94 O 8 1.01 69.

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Fig. 6. Probability of the modal response for each of the 210 stimuli tested in the experiment.

For each stimulus, the subjects'

responses have been pooled. This yields

100 color naming responses for each of

the stimuli. In Figures 3, 4, and 5, color

naming boundaries have been plotted

based on the modal response to each

stimulus and a 95% (Figure 3), 75% (Figure 4), and 50% (Figure 5) criterion.

That is, the colors within these boundaries have a modal response greater

than or equal to the criterion. At the

95% criterion, there are only greens,

blues, and purples in the stimulus set.

When the criterion was dropped to 75%,

yellow, pink, orange, and aqua regions

were added. The failure to obtain a color

that was named red at least 75% of the

time is not surprising for it is a well

known fact that the "red" phosphor utilized on many CRT screens is not a highly saturated red. At the 50% criterion,

nine of the ten color names (all except

white) have specified regions in the

color space. Lastly, Figure 6 gives the

probability of the modal responses to

each of the 210 stimuli.

DISCUSSION

As stated in the Introduction, the

results of this experiment will serve as a

data base which will allow a comparison

of strategies for the selection of easily

distinguishable colors for color sets.

One strategy is to choose colors with different color names, using one or more of

the regions established by varying the

modal criterion in this experiment (Post

& Greene, 1986; Post & Calhoun, 1988).

6
75% BOUNDARY

94%

A

"78%

B C

Fig. 7. Colors A and B were called green at least 75% of the time, whereas color C has been called

green only 39% of the time. However, the distance between colors A & B and B & C are equal.

Another strategy is to select colors

which exceed a minimal delta E value

for all possible color pairs in the set.

Delta E refers to the difference between

two colors in CIE LUV (Silverstein and

Merrifield, 1985) space, taking into account both brightness and chromatic differences. Neri, Jacobsen, & Luria (1985)

showed that the latter strategy was useful in predicting color matching performance with color sets recommended in

the literature.

The two strategies could be at odds

under the following conditions. First,

the color naming strategy may recommend two or more colors for inclusion in

the set that do not exceed the criterion

delta E value even though they were

reliably called by different names.

Second, the color discrimination

strategy may recommend two or more

colors for inclusion in the set that come

from the same color naming region even

though they exceed the criterion delta E

value. This situation is illustrated in

Figure 7. Colors A and B have been

called green at least 75% of the time

(94% for color A, 78% for color B),

whereas color C falls outside this green

color region. However, the distance between colors A and B is equal to the distance between colors B and C. If delta E

is a reliable predictor of discriminability

then one would predict that colors A and

B are as discriminable from one another

as colors B and C. However, if color

naming has an effect on discriminability,

then A and B may prove more difficult to

discriminate than B and C. The same

holds true for an identification task, or a

paired-associate learning task. In each

of these tasks we may ask how effective

the color naming regions are in predicting performance with colors drawn from

different regions.

The issue is not a simple one since

many variables come into play. To

name just two, there is the role that the

relative weight of luminance differences

plays in determining delta E with the

color discrimination strategy, and the

role the proximity of two differently

named colors in 1976 CIE space plays

with the color naming strategy. The

core issue may be whether the application of different color names to two

stimuli serves to enhance their perceptual discrimination, or whether

7
perceptual discrimination is devoid of

this cognitive influence. Since there appears to be a primacy to certain named

colors (Ratliff, 1976), we suspect that attention to the names ascribed to two

color stimuli in examining their discriminability may play at least as large

a role as their difference computed by an

algorithm based on their Euclidean distance in a roughly perceptual space.

The results of this experiment provide

the data base with which to compare the

two strategies.

REFERENCES

Neri, D. F. (1990). Color CRT characterization presented solely in terms of

the CIE system. Perceptual and

Motor Skills, Vol 71, pg 51 - 64.

Neri, D. F., Jacobsen, A. R., and Luria,

S. (1985). An evaluation of color sets

for CRT displays (NSMRL Report

1068). Groton, CT: Naval Submarine

Medical Research Laboratory.

Post, D. L. and Calhoun, C. S. (1988).

Color-name boundaries of equally

bright stimuli on a CRT: Phase II.

SID Digest, pg 65 - 68. N.Y., NY:

Palisades Institute.

Post, D. L. and Greene, F. A. (1985).

Color naming as a function of

stimulus luminance, angular subtense, and practice. Proceedings of

the Human Factors Society - 29th annual meeting (pg 1070 - 1074). Baltimore, MD: Human Factors Society.

Post, D. L. and Greene, F. A. (1986).

Color-name boundaries for equally

bright stimuli on a CRT: Phase I. SID

Digest, pg 70-73. N.Y., NY:

Palisades Institute.

Ratliff, F. (1976). On the psychological

bases of universal color terms.

Proceedings of the American

Philosophical Society, Vol 120, #5,

Oct, pg 311- 330.

Robertson, A. R. (1977). The CIE 1976

color-difference formulae. Color Research and Application, Vol 2 #1,

Spring , pg 7-11.

Silverstein, L. D. and Merrifield, R. M.

(1985). The development and evaluation of color systems for airborne applications. Phase I. Fundamental,

visual, perceptual, and display system considerations. Final Report (B6-

53012). Department of

Transportation, FAA PM 85/19.

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Frequency of color names for colors generated on a CRT

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19. ABSTRACT(Continue on reverse if necessary and Identify by block number)

Color naming frequency data were collected for 210 equiluminant colors. These colors

represent a sample of the color space realizable on a CRT screen. From these data, color

naming boundaries were constructed utilizing criteria of 50%, 75%, and 95%. The results of

this experiment provide a data base with which to compare alternative strategies for the

application of colors to CRT displays.

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