Naval Submarine Medical Research Laboratory

NSMRL REPORT 1189 10 SEPTEMBER 1993

AD-A275 196 III I Iitt ll MIII II i IIIIIl

THE RELATIVE EFFECTIVENESS OF FOUR COLOR CODING TECHNIQUES

FOR INTENSITY CODING ON SIMULATED

ADVANCED MINE DETECTION SYSTEM (AMDS) DISPLAYS

Kevin Laxar, D Iu C

Joseph DiVita, E L.EC E •1

Susan E. Gallagher, 84 9 U

Sandra L. Benoit

Released by 94-02568

P. K. Weathersby, CAPT, MSC, USN I II il III III I I Ii

Commanding Officer

Naval Submarine Medical Research Laboratory

.,,Approved for public release; distribution unlimited

94 1 26 043
THE RELATIVE EFFECTIVENESS OF FOUR COLOR CODING TECHNIQUES

FOR INTENSITY CODING ON SIMULATED

ADVANCED MINE DETECTION SYSTEM (AMDS) DISPLAYS

Kevin Laxar, Joseph DiVita,

Susan E. Gallagher, and Sandra L Benoit

Naval Submarine Medical Research Laboratory

Report 1189

Naval Medical Research and Development Command

Research Work Unit No. 65865N M0100.001-5003

fAccesion For

NTIS CRA&I

OTIC I-AB

U• lannounced 0

Justificationl.....---------

Approved and Released by: • • ~ .............. ~~By ....-------

9 099 Distribution I

- Availability codes

P. K. Weathersby, CAPJU, MSC, USN Avail and I or

Commanding Officer Dist Special

Apoe QUALITY INppEClED 5

Approved for public release; distribution unlimited
SUMMARY PAGE

THE PROBLEM

To determine which of four color schemes would be most effective for coding the eight intensity

levels of sonar signals on CRT displays for the Advanced Mine Detection System (AMDS).

FINDINGS

The ability of observers to detect and identify sonar targets on simulated AMDS displays was

measured for one existing and three proposed color coding schemes at several target signal strengths.

One proposed color coding scheme was found to afford significantly superior performance, especially at

lower signal-to-noise ratios.

APPUCATION

Colorimetric specifications of the coding scheme shown to provide enhanced target detection are

provided, for implementation on the AMDS.

ADMINISTRATIVE INFORMATION

This study was conducted at the Naval Submarine Medical Research Laboratory under Naval Medical

Research and Development Command Research Work Unit No. 65856N M0100.001-5003, Enhanced

performance with visual sonar displays. The views expressed in this report are those of the authors and

do not reflect the official policy or position of the Department of the Navy, the Department of Defense,

or the United States Government. The manuscript was approved for publication on 10 September 1993

and designated as NSMRL Report No. 1189.

ii
Abstract

Four methods of color coding the intensity levels of sonar returns on the Advanced Mine Detection

System displays, currently under development, were studied to determine how the added use of color

could enhance operability. The target detection and identification performance of seven experienced

observers was measured using the following schemes for coding signal intensity into eight discrete

steps: levels of green (the original coding method), levels of white, colors approximating specifications

supplied by the Naval Undersea Warfare Center (NUWC), and colors arranged according to lightness,

from dark to light. A portion of a static AMDS display 726 pixels wide by 323 pixels high was simulated on a computer controlled color display system. A single target, simulating six sonar pings, or

histories, was six pixels wide (10.2 arc min visual angle) by one pixel high, and was present on 50% of

the trials. It could be located anywhere in the background. Four target signal strengths were used. The

randomized distributions of the background noise levels and the target levels were specified by NUWC

and considered to be representative of those expected at sea. Each observer ran on two 100-trial

sessions of each of the 16 conditions, combinations of one of the four target strengths and one of the

four color coding schemes. In a signal detection paradigm, for each trial the observer signalled, by key

press, confidence in the presence or absence of a target on a four-point scale, and indicated the location

of the ta3rget, when present, by means of a trackball cursor. The hit rates (percentage of trials on which

the observer correctly declared the presence of a target), false alarm rates (percentage of trials on which

the observer incorrectly declared the presence of a target), and percentage of correct target identification

(location) were computed. Results showed that for the two strongest target levels, the fbur color coding

schemes all produced uniformly high performance. For the two weakest target levels, at a false alarm

rate of 5%, analyses of variance showed that the color scheme specified by NUWC was superior to the

other three in both hit rate and target identification. This superiority became more evident as target

strength (i.e., signal to noise ratio) decreased. This color scheme uses highly saturated colors with the

representation of signal intensity directly related to both luminance and to the wavelength of the visible

spectrum. Colorimetric specifications of the color schemes tested are provided.

111..
[Blank Page]

iv
THE RELATIVE EFFECTIVENESS OF FOUR COLOR CODING TECHNIQUES

FOR INTENSITY CODING ON SIMULATED

ADVANCED MINE DETECTION SYSTEM (AMDS) DISPLAYS

Typical CRT display screens of submarine color coding techniques would compare with

systems in the past have been monochrome. intensity coding of only the green phosphor

Specifications for coding signals in many for detection and identification (localization

current sonar display systems are therefore on the screen) of a significant signal. For exwritten in terms of intensity levels on mono- ample, combining values from the red and

chrome displays. Current technology, how- blue guns with that from the green to make

ever, now permits color CRT displays of high white would add to the luminance of that

reliability and resolution, and these are being pixel. The range of luminance from the zero

incorporated into the latest shipboard systems. background to the maximum white would

The question arises, then, of how best to make therefore be greater than the luminance range

use of this color capability in these systems. of only the green gun, thus permitting a

It would be beneficial to know whether the greater amount of luminance change between

use of color could enhance the operability of the intervening adjacent steps. This might afthe display, and if so, how. ford better distinguishability among the levels

and enable the operator to discern signals

Of concern in this study is coding the in- more easily.

tensity levels of sonar returns on the display

for the Advanced Mine Detection System Another alternative would be to code the

(AMDS) being developed by IBM under the signal intensity as different colors and lumidirection of the Naval Undersea Warfare Cen- nances on the screen, with the same goals as

ter (NUWC), New London Detachment, Code above. This approach has been tried before,

2123. This system uses active sonar to detect with various results. In a study by Butler and

small underwater objects such as mines, dis- McKemie (1974), performance was compared

playing bearing along the horizontal axis and using seven different color codes and one

range along the vertical axis. The intensity of gray-scale code for displaying seven or eight

the sonar return is coded in the initial version intensity levels on simulated sonar displays.

of the system as proportional to pixel lumi- Observers signalled the presence of targets on

nance on the green phosphor display screen. displays containing noise backgrounds. The

Intensity is coded using a three-bit scheme probability of detection, or hit rate (percentinto one of eight luminance steps, from zero age of trials in which the observer said a tar-

(same as the dark screen background) to the get was present when it in fact was), and false

brightest green available (maximum green alarm rate (percentage of trials in which the

gun value for the CRT). In such displays, the observer said a target was present and it was

target, on the average, gives a more intense not) were measured. Results showed differsignal return than the background noise and is ences in probability of detection among the

thus perceived as a brightened area. With the seven color codes, and that all color codes

proposed use of a color CRT for this display, were superior to the admittedly non-optimum

NUWC raised the question of how alternative gray-scale code over the range of 10 signal to

1
noise ratios tested. The false alarm rate was hue. No differences were found among the

low and essentially constant across all condi- four codes, either for probability of detection,

tions. The authors concluded that the best probability of false alarms, or minimum deteccodes were those in which the colors were tion level at any of the seven signal to noise

linearly related to a predetermined subjective ratios tested.

measure of conspicuousness, which was

highly correlated with luminance. It was ap- Using color schemes similar to those used

parent that these codes were also most by Salafia, et al. (1988, 1990), Douglas

broadly distributed over the available chro- (1988) found that observers generally subjecmaticity space. tively preferred using monochrome green

over colors for target detection, but collected

In a somewhat different task, French no performance data.

(1978) found no difference in pattern detectability thresholds between three gray scales Another study also failed to show a benefiand three color coding scales, each having 8, cial effect of color coding in a sonar detec16, or 60 levels cf hue and luminance coding tion/classification task (Glenn, Zaklad, Ryder,

combinations. & Goodman, 1991). Response times were

compared for finding targets using each of

A study by Kraiss and Kfittelwesch (1984) three color codes, a standard monochrome encompared signal detection performance on coding, a color code that had been chosen by

simulated sonar displays using seven coding the group of subjects for preferred brightness

schemes at three combinations of background and color in a previous signal detection experinoise variance and signal to noise ratio. Two ment, and an adjustable color code in which

of the codes were white on a black back- the subjects could vary the colors to suit their

ground and the reverse. The other five used preference. Response times were slightly but

from three to 12 colors at various luminance significantly faster for the monochrome scale

coding schemes. Two of the color codes than for either of the two color coding

showed superior performance at a low signal schemes. The authors concluded that the efto noise ratio with zero background noise vari- fectiveness of color coding sonar detection

ance. As noise variance increased, however, displays is still an open question and that furthese codes showed significantly poorer per- ther exploration of color codes is required.

formance than the other codes. The authors

concluded that there was no evidence that Given the lack of clear and concise human

color can facilitate the signal detection task. factors recommendations on this issue, the present research was conducted to compare alterIn a more recent study (Salafia, DaRos, & native coding schemes in order to provide

Boivin, 1988; Salafia, 1990), performance on NUWC with recommendations for the AMDS

a simulated sonar detection task was com- display. In this study, we simulated a portion

pared for one monochrome green-scale code of a static AMDS display and compared operaand three color codes of seven signal intensity tors' detection and identification performance

levels. Two of the color codes used only two using four coding schemes: levels of green,

hues and the third used four. For all codes the levels of white, colors approximating NUWC

four highest signal intensity levels were en- specifications, and colors arranged in order of

coded as increasing luminance of the same lightness, from dark to light.

2
Method

Table 1

Percentages for Simulated Background Observers Noise by Display Level

Seven females 21 to 32 years old (mean =Lve Perent

29.6 years) were paid for observing. All had 0 83.89

normal or corrected vision for the viewing dis- 1 12.36

tance, and all had prior experience with visual 2 3.18

*psychophysics experiments. 3 4 0.51 0.056

5 0.004

Experimental Design 6 0

A two-factor (four levels of target 7 0

strength x four color coding scheme.S) within

subjects (repeated measures) design was used.

All observers were given two 100-trial ses- played as display Level 0, or black, for all

sions under each of the 16 conditions of target color schemes investigated here. Percentage

strength and color coding scheme. The order of the background noise pixels illuminated

of the experimental conditions was random- then rapidly decreases with increasing display

ized for each observer. level, approaching zero at Levels 6 and 7. In

fact, no background pixels representing LevApparatus els 6 and 7 were illuminated, due to computer

The sonar displays were simulated on a constraints in representing infinitesimal probRamtek 9400 high resolution color display abilities. A different pattern of random noise

system controlled by a DEC VAX minicom- was used for each trial.

puter. Observers responded using a standard

computer terminal keyboard and a Ramtek A target, simulating six sonar pings, or histrackball. The terminal display was used to tories, was six pixels (1.7 mm, or 10.2 mingive the observer informational prompts and utes of arc) wide by one pixel high. A target,

knowledge of results, as described below, when present, could be located anywhere

The experimental room was dimly and indi- within the background. Four target signal

rectly illuminated by a fluorescent desk lamp strengths were used, from weak (No. 1) to

located behind the display monitor. strong (No. 4). They were assigned to intensity levels in the four color schemes according

Sonar Displays to the algorithm shown in Table 2, as speciFor each trial, a display consisting of simu- fied by Code 2123, NUWC, in accordance

lated randomized background noise was pre- with the type of data expected from actual tarsented on the screen 726 pixels wide by 323 gets at sea. The highest signal strength (No.

pixels high, measuring 19.6 cm wide by 7.9 5) was not used because pilot experiments incm high. At the typical viewing distance of dicated that the task in that case was too easy

57 cm, this subtended a viewing angle of and therefore no worthwhile data would be

19.60 wide by 7.90 high. The distribution of collected. This meant that only coding of Levthe background noise levels was considered els 0 through 6 were used in this experiment;

by NUWC to be representative of that ex- Level 7 was never displayed.

pected at sea, and is given in Table 1. The

preponderance of the noise background is dis3
Table 2

Algorithm for Determining Target Intensity Levels for Five Target Signal Strengths

1. For each target define:

Target

Signal

Srength Shift Variability

1 1 3

2 1 5

3 3 2

4 3 3

5 4 4

2. Generate a uniform number (X) between 0 and 1.

3. Compute display level directly as follows based on values defined above:

Intensity Level = Shift + X * Variability.

If Intensity Level > 7, set Intensity Level = 7.

4. Repeat for each history.

Note. In these experiments only Target Signal Strengths of I through 4 were used, so Intensity Level never

exceeded 6.

Color Schemes tween the two extremes. The colorimetric

specifications are given in Table 3. SuccesGreen. The display that encoded signal sive levels of green had a luminance increase

intensity in luminance levels of green was de- over its preceding level by an average factor

fined first, with Level 0 being black, that is, of V'1.73. A factor of V-, typically used for

having gun values of zero, and Level 7 having scaling intensity on actual sonar displays, was

the maximum green gun value. The six inter- not achievable due to limitations of display

vening values were psychophysically scaled system. All colorimetric measurements were

to approximate equal brightness steps be- made using a PR-703A/PC SpectraScan fast

Table 3

Colorimetric Specifications of CRT Stimuli for Signal Level Coded by Luminance of Green

Level & x y u' v' Dominant Excitation

Nominal Luminapce Wavelength Purity

Color (cd/mi) (nm) (%)

1 Green 08.7 .284 .605 .117 .562 523 46.6

2 11.1 .284 .606 .117 .562 523 46.7

3 15.6 .284 .606 .117 .562 523 46.9

4 22.0 .284 .607 .117 .562 523 47.1

5 29.1 .284 .607 .117 .562 523 47.1

6 35.4 .283 .607 .117 .562 523 47.1

7 44.4 .283 .607 .117 .562 523 47.1

Note. The x and y values are the chromaticity coordinates on the CIE 1931 chromaticity diagram. The u'

and v' values are the coordinates on the CIE 1976 Uniform Chromaticity Scale diagram.

4
Table 4

Colorimetric Specifications of CRT Stimuli for Signal Level Coded by Luminance of White

Level & x y u' v' Dominant Excitation

Nominal Luminance Wavelength Purity

Color (cd/m ) (nm) (%)

1 White 12.9 .295 .294 .199 .445 481 42.7

2 16.1 .296 .297 .198 .448 481 42.1

3 23.2 .299 .297 .201 .448 481 41.4

4 32.7 .302 .296 .203 .448 480 40.7

5 44.2 .299 .292 .202 .445 480 41.2

6 55.9 .299 .289 .204 .443 479 42.0

7 65.3 .295 .287 .202 .441 479 43.1

Note. The x and y values are the chromaticity coordinates on the CIE 1931 chromaticity diagram. The u'

and v' values are the coordinates on the CIE 1976 Uniform Chromaticity Scale diagram.

spectral scanning system (Photo Research each step (except Level 0, which was black)

Div., Kollmorgen Corp.). CRT gun values averaged 50% greater than the corresponding

are not given because of the vast differences level on the green display, and so the steps

in display systems and CRT screens. between each level as well as the total luminance range of the white display were 50%

White. The next display specified was greater than those of the green display.

the "white" encoded scheme. For each of the Again, the successive levels of white ingun values specified for the green display, ap- creased by an average factor of Vi73. The

propriate amounts of red and blue were added specifications for this display are given in

to make an acceptable white, resulting in a dis- Table 4.

play of eight levels from black to the brightest

white available on the CRT display, again in NUWC. The color coded display speciapproximately equal steps. The luminance of fled by NUWC Code 2123 using CRT gun

Table 5

Colorimetric Specifications of CRT Stimuli for Signal Level Coded by NUWC-Specified

Colors

Level & x y u v' Dominant Excitation

Nominal Luminance Wavelength Purity

Color (cd/m") (nm) (%)

I Dk Blue 00.8 .185 .211 .143 .368 481 73.2

2 Blue 05.9 .168 .132 .158 .279 474 83.7

3 DkGreen 22.7 .251 .473 .123 .521 501 44.7

4 Green 40.6 .266 .537 .120 .542 508 41.3

5 Orange 50.5 .505 .439 .279 .544 584 61.8

6 Yellow 65.8 .465 .470 .241 .549 575 55.4

7 Red 26.9 .576 .320 .405 .507 508a 53.3

Notes. The x and y values are the chromaticity coordinates on the CIE 1931 chromaticity diagram. The u'

and v' values are the coordinates on the CIE 1976 Uniform Chromaticity Scale diagram.

a This is an extraspectral hue, between red and violet, plotted on the CIE 1931 chromaticity diagram as complementary to the given wavelength.

5
values for a given display system was visually to be effective in the Butler and McKemie

approximated on NSMRL's Ramtek system. (1974) study. Finally, it had the intuiti-,e apThis code of eight levels was an approximate peal of lighter colors indicating greater signal

subset of 16 colors recommended to NUWC intensity. The specifications are given in Taby the Applied Research Laboratory at the ble 6, where one can see that with the excepUniversity of Texas (ARL'UT). The latter tion of red (Level 4), luminance of the colors

code had Level 0 as black, four increasing lev- increases with their lightness.

els of blue. five increasing levels of green,

four increasing levels of yellow, one level of Procedure

red, and the highest level as white. The eight The experiment was self paced. Obcolorimetric values used in the present study servers were told to work accurately and that

are given in Table 5. there were no time limits, and that a target

would be present on only 50% of the trials.

Lightness. An additional color coded dis- The observer pressed the Enter key to start

play scheme was designed by the authors at each trial. The display then took approxiNSMRL based on order of lightness of color, mately 2 s to appear line by line on the screen.

with Level 1 a dark blue and Level 7 white. A signal detection paradigm (Swets, Green,

This scheme was chosen for test for several Getty, & Swets, 1978) was employed, in

reasons. First, it was another approximate which the observer first scanned the display

subset of the 16 colors recommended by and decided upon the presence or absence of a

ARL/UT. Second, both this and the NUWC target. She then keyed in a confidence rating

specified code had luminance highly corre- of her judgment, as follows: 1 - certain there

lated with signal intensity level, found to be is no target; 2 - somewhat sure there is no tareffective by Butler and McKemie (1974). get; 3 -somewhat sure that there is a target;

Third, as also true of the NUWC code, it used and 4 - certain that there is a target. The termicolors widely spaced in chromaticity, shown nal screen then indicated to the observer the

Table 6

Colorimetric Specifications of CRT Stimuli for Signal Level Coded by Order of Lightness of Color.

Level & x y u' v Dominant Excitation

Nominal Lumina9 ce Wavelength Purity

Color (cd/m) (nm) (%)

1 Violet 10.0 .197 .097 .209 .231 460 82.5

2 Blue 17.5 .154 .070 .175 .178 467 93.1

3 Green 42.4 .266 .533 .120 .541 508 41.4

4 Red 26.6 .576 .321 .404 .507 507a 53.1

5 Orange 51.0 .504 .440 .277 .545 584 61.8

6 Yellow 66.3 .463 .471 .240 .549 575 54.7

7 White 68.6 .277 .257 .202 .418 477 49.2

Note. The x and y values are the chromaticity coordinates on the CIE 1931 chromaticity diagram. The u'

and v' values are the coordinates on the CIE 1976 Uniform Chromaticity Scale diagram.

a This is an extraspectral hue, between red and violet, plotted on the CIE 1931 chromaticity diagram as complementary to the given wavelength.

6
correctness of her choice, that is, whether schemes was seen. All produced uniformly

there actually was a target in the display or high levels of performance.

not. If a target was present, the observer was

prompted to place a trackball cursor over it For the two weakest or most difficult to

and press Enter on the keyboard, to determine detect target levels, significant differences

itf the target was correctly located, or "identi- were found among color coding schemes.

fied." The computer terminal then gave a The data for the hit rates and for the correct

message as to the correctness of the location identification percentages for the false alarm

and recorded the observer's performance for rate of 5% were subjected to separate repeated

each trial. The observer continued until the measures analyses of variance (ANOVAs).

100 trials for that session were completed. Be- For hit rate, the difference between the two

fore the experiment, the observer was given a target levels was highly significant, F(1, 6) =

brief practice session with each of the four 340.2, p < .001, with, as expected, the

color schemes. Each session took from 25 to stronger of the two being much easier to de50 minutes to complete, depending upon the tect. The mean hit rate for Target Level 1 was

difficulty of finding the target. 15.3% and for Target Level 2, 59.5%. The interaction between Target Level and Color

Results Code did not approach significance, as the difference between the two target levels was

A confidence rating scale of 1 through 4 nearly the same for all four color codes. The

generates three points on the observer's Re- effect of color coding scheme was also highly

ceiver Operating Characteristic (ROC) curve significant, F(3, 18) = 10.4, p < .001. The

(Swets, et al., 1978), which is a plot of false

alarm rate on the x-axis versus hit rate on the

y-axis. As customary, these rates were converted to z-scores prior to further analyses. 60

For each observer a line was fit through these

points, plotted in terms of z-scores, by the so 5

least squares method with slope and intercept

as free parameters. A hit rate that corre- 40 -

sponded to a false alarm rate of 5% (z = - 7

1.65) was then determined. This false alarm 30 -

rate was chosen due to its being an operationally meaningful level of performance. In a 20 .

similar fashion, the rating technique yields

three points in the false alarm rate by percent- 1 .

age correct identification (PCI) space (with .

false alarm rate on the x-axis and PCI on the - - , -

y-axis). For each observer, a best fitting line Gren Wh•te NUWC tLghtnes

was determined and the PCI for a false alarm Color Coding Schene

rate of 5% was computed.

Figure 1. Mean percentage Hits for the two most

For the two strongest target levels, very lit- difficult target levels combined, at a False Alarm

tie difference among the four color coding Rate of 5% for the four color coding schemes.

7
percentage of hits for both target levels com- Target Level I

bined are shown for the four color coding Target Level 2 M

schemes in Figure 1. A post hoc Newman- 100

Keuls test showed that the NUWC color cod- 9o .

ing s, eme was significantly different from so .

the other three schemes, p < .01, which were

not significantly different from each other, 70 -

p > .05. so •

For percentage correct identification, - 40 •

again target level was significant F(1, 6) =30

31.6, p < .005, and a significant difference 0

was found for color coding scheme, F(3, 18)

= 5.6, p < .01. The percentages for each color 10

coding scheme are shown in Figure 2. A Green White NUWC Lightness

Newman-Keuls test showed that the NUWC Color Coding Scheme

colors were significantly different from the

lightness color code, p < .01 and the green Figure 3. Mean percentage Correct Identification

code, p < .05, but not significantly different for Target Levels 1 and 2 at a False Alarm Rate of

from the white code, p > .05. The green, 5% for the four color coding schemes.

white, and lightness color codes were not significantly different from each other. The

interaction between color code and target

level was also significant, F(3, 18) = 7.5,p <

.005. At Level 2, the four codes yield similar

100 PICs, whereas at the weakest level, Level 1,

the NUWC code is far superior to the other

three (Figure 3).

C Discussion and Conclusions

=.

* so

_ For the AMDS displays as simulated here,

1 70 - for both detection of a six-pixel wide target

and identification of its location within a display of background noise, the color coding

scheme as specified by NUWC has been

shown to be superior to coding by intensities

so rof green, white, or by an alternative color codGrow White NUWC Ughtness ing scheme tested here. This superiority beColor Coding Scheme comes more evident as target strength (i.e.,

signal to noise ratio) decreases.

Figure 2. Mean percentage Correct Identification of

target for the two most difficult target levels These results confirm those of previous

combined, at a False Alarm Rate of 5% for the four research that, when properly chosen for the

color coding schemes.

8
particular set of display conditions, a color level correlates with the spectral order of

coding scheme can prove superior to a mono- dominant wavelength. If signal intensity were

chrome intensity scale (Butler & McKemie, additionally coded by increasing levels of

1974), but in other cases may not enhance luminance, as both the NUWC and the Lightperformance over monochrome schemes ness color codes roughly were, color coding

(Glenn, et al., 1991; Salafia, 1990; Salafia, would be redundant, as discussed in the preet al., 1988). vious paragraph, and may not add to the overall effectiveness of the display. Salafia's

Why the NUWC color code proved effec- point, here, however is that the redundant

tive here remains a question. The colors were coding would at least not present conflicting

well separated in chromaticity space and their scales of the same information and thus would

luminances were highly correlated with coded not interfere with operator performance. The

intensity level (except for the highest level, correlation coefficients of signal intensity

which was red), as suggested to be most effec- level with luminance and with dominant wavetive by the Butler and McKemie (1974) study. length for both the NUWC code and the LightOn the other hand, the color code was redun- ness code were calculated. The correlation of

dant with luminance, which as discussed by intensity with luminance is reasonably high

Salafia, et al. (1988) might be ignored by the for both codes, r = .74 for the NUWC code

operator and not enhance performance at all. and r = .94 for the Lightness code, despite the

In addition, the alternative color scheme non-monotonicity due to the red in each

(Lightness) also tested here had very similar scheme (see Tables 5 and 6). The correlation

characteristics to the NUWC scheme, yet of intensity with dominant wavelength for the

proved no more effective than the two mono- NUWC code is r = .90, however, while that

chrome schemes. These two color schemes for the Lightness code is r = .30. It must be

looked quite different on the display due to concluded that order according to dominant

the mapping onto the intensity distribution of wavelength is indeed a powerful determinant

the background noise. As shown in Table 1, of a color code's effectiveness.

the preponderance (99.43%) of the background noise pixels were coded at intensity An additional conclusion of the Butler and

Levels 0, 1, and 2, with Level 0 being black in McKemie (1974) study was that displays

all cases. Levels 1 and 2, however, totalled whose colors were rated as harmonious

over 15% of the background. For the NUWC afforded better performance than those whose

scheme, Levels 1 and 2 were coded into dark colors were judged as being unpleasant, a

blue and blue of low luminances (see Table factor that may have entered into the present

5), whereas the Lightness scheme coded these study. The colors in the NUWC scheme,

levels into violet and blue of much higher especially at Levels 0 through 2 may have

luminances (Table 6). The effect of this was been more harmonious or so dark that they

to make the Lightness display look generally did not appear unpleasant, whereas the Lightmuch brighter than the NUWC display, and ness scheme may not have had this subjective

perhaps this caused the bright targets to be advantage. A related issue discussed by

more difficult to detect. Kraiss and Kfittelwesch (1984) and Salafia

(1988), and perhaps more to the point, is

Another issue, which Salafia, et al. (1988) chromatic noise, or colored "snow" on the

have suggested, is that the signal intensity display screen, in which color could add to

9
the masking effect on the target by the ampli- (highest excitation purity) available on the

tude noise already inherent in the display. display system.

The more uniform background brightness of

the Lightness display may have hindered de- Figure 4 shows the locations on the chrotection performance relative to the NUWC maticity diagram of the NUWC code colors

display scheme. and the green and white scales, as well as the

chromaticity boundaries of the phosphors on

The results of this research provide evi- the display monitor used in this study. One

dence that to the extent the at-sea conditions can see that the NUWC colors lie at the

of background noise and target signal strength boundary of the most saturated colors availwere accurately simulated, the color coding able. Spectral order proceeds from blue

scheme as specified in Table 5 would be through green to yellow and red, with colors 1

highly appropriate for use on the AMDS and 2 transposed, and colors 5 and 6 transdisplay. This coding scheme can be generally posed. (For color 7, a small amount of blue

characterized as having the representation of was added to the red to make it look less orsignal intensity directly related to both lumi- ange. This also added very slightly to its

nance and to the wavelength of the visible brightness.) If achievable on a display, a

spectrum, while having the colors lie at the possibly better coding scheme would have

outermost parts of the chromaticity space so highly saturated colors completely in spectral

as to present the most saturated colors order, perhaps spaced further apart perceptually, while at the same time having their

respective luminances increase from a very

low level to the maximum. The concept of

combining high saturation and spectral order

that is correlated with luminance may well

0.8 prove to be the basis for color coding schemes

for the types of displays studied here that have

G applicability under a wide range of situations,

4 including number of intensity levels.

3

So0.4 As Butler and McKemie (1974) pointed

W .out, however, the choice of a color coding

0.2- + scheme must depend on such factors as the

0 characteristics of the signal and the noise, the

color and resolution characteristics of the

0.0o , , display system, and the operator's task. Only

0.0 0.2 0.4 0.6 0.8 some of the nearly infinite number of color

X coding schemes apparently are effective for a

given set of conditions. The authors mentioned above, and ourselves, agree that more

Figure 4. Coordinates of the Green (G), White (W), systematic studies of coding in the color space

and NUWC (1-7) color coding schemes on the CIE are required.

1931 chromaticity diagram. The triangle is the

boundary of chromaticities available on the display

system used in this study.

10
Acknowledgment in passive sonar displays (NUSC Technical Report No. 8277). New London, CT:

The authors express their gratitude to Mr. Naval Underwater Systems Center. (ADLee Shapiro of NSMRL for the computer pro- A197 283)

gramming of this experiment.

Swets, J. A., Green, D. M., Getty, D. J., &

References Swets, J. B. (1978). Signal detection and

identification at successive stages of obserButler, W. B., & McKemie, W. M. (1974). vation. Perception & Psychophysics. 23,

Final Report: Engineering Guidelines for 275-289.

the use of color in a sonar display (Document No. T73-AU-9550-U (REV)).

Austin, TX: Tracor Sciences & Systems.

Douglas, H. J. (1988). Color as a means of

improving target detection in sonar gram

displays (NUSC Tech. Memo. TM

881175). New London, CT: Naval Underwater Systems Center.

French, R. S. (1978). Grey-scale versus

color coding of acoustic data images

(Tech. Report 207). San Diego: Naval

Ocean Systems Center.

Glenn, F. A., III, Zaklad, A. L, Ryder, J. M.,

& Goodman, L. S. (1991). Experimental

evaluation of an adaptable acoustic color

coding interface system. Proceedings of

the Human Factors Society 35th Annual

Meeting, 1471-1475.

Kraiss, K.-F., & Kiittelwesch, K.-H. (1984).

Color and gray scale in sonar displays. Society for Information Display 84 Digest,

68-71.

Salafla, W. R. (1990). Target detection performance as a function of color in sonar

gram displays (NUSC Technical Report

No. 8647). New London, CT: Naval Underwater Systems Center. (AD-B148 507)

Salafla, W. R., DaRos, D. A., & Boivin, P. R.

(1988). Color coding of amplitude data

as a means of improving target detection

11
[Blank Page]

12
UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS PAGE

Form Approved

REPORT DOCUMENTATION PAGE O04 No. 074-18

la. REPORT SECURITY CLASSIFICATION lb. RESTRICTIVE MARKINGS

UNCLASSIFIED

2a. SECURITY CLASSIFICATION AUTHORITY 3. DISTRIBUTION/AVALABILUTY OF THE REPORT

ApproVed for nubliq release;

2b. DECLASSIFICATION/DOWNGRADING SCHEDULE dibtribution tinimited

4. PERFORMING ORGANIZATION REPORT NUMBER(S) 5. MONITORING ORGANIZATION REPORT NUMBER(S)

NSMRL Report 1189 NA

Sa. NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION

Naval Submarine Medical (I ,;lii) Naval Medical Research and Development Research Laboratory Ccmnand

6c. ADDRESS (City. Sate, Zip Code) 7b. ADDRESS (City, State, Zip Code)

Naval Submarine Base NLON, 8901 Wisconsin Avenue, Bethesda, MD

Groton, CT 06349-5900 20889-5606

8a. NAME OF FUNDING/SPONSORING 8b. OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER

ORGANIZATION (ff Apphcatbe)

Same as 7a I

8c. ADDRESS (City, State, Zip Code) 10. SOURCE OF FUNDING NUMBERS

Same as 7b PROGRAM PROJECT NO. TASKNO. WOK UNIT

ELEMENT NO. ACCESSION NO.

65856N M0100 1001 DN245505

11. TITLE (Include Security Classification)

The Velative effectivengss of four color codinq techniques for intensity coding

on simulated Advanced Mine Detection System (ARDS) displays

12. PERSONAL AUTHOR(S)

Kevin Laxar, Joseph DiVita, Susan E. Gallaqher, and Sandra L. Benoit

13a. TYPE OF REPORT 13b. TIME COVERED 14. DATEOFFEPORT (Yma, rbE D* y 15. PAGE COUNT

Interim FROM TO 11993 SEP 10 12

16. SUPPLEMENTARY NOTATION

17. COSATI CODES 18. SUBJECT TERMS (Continue on revrse if necessary and identify by block number)

FIELD GROUP SUB-GROUP .Dcision making, Tactical displays, Human subjects, Visual sonar displays, Perforthance

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

Four methods of color coding the intensity levels of sonar returns on the Advanced Mine Detection System displays,

currently under development, were studied to determine how the added use of color could enhance operability. The

target detection and identification performance of seven experienced observers was measured using the following

schemes for coding signal intensity into eight discrete steps: levels of green (the original coding method), levels of

white, colors approximating specifications supplied by the Naval Undersea Warfare Center (NUWC), and colors

arranged according to lightness, from dark to light. A portion of a static AMDS display 726 pixels wide by 323

pixels high was simulated on a computer controlled color display system. A single target, simulating six sonar pings,

or histories, was six pixels wide (10.2 arc min visual angle) by one pixel high, and was present on 50% of the trials. It

could be located anywhere in the background. Four target signal strengths were used. The randomized distributions

of the background noise levels and the target levels were specified by NUWC and considered to be representative of

those expected at sea. Each observer ran on two 100-trial sessions of each of the 16 conditions, combinations of one

of the four target strengths and one of the four color coding schemes. In a signal detection paradigm, for each trial

the observer signalled, by key press, confidence in the presence or absence of a target on a four-point scale, and

indicated the location of the target, when present, by means of a trackball cursor. The hit rates (percentage of trials

20. DISTRIBUTION/AVAILABILITY OF ABSTRACT 21. ABSTRACT SECURITY CLASSIFICATION

X UNCLASSIFIED/UNLIMITED SAME AS REPORT DTIC USERS

22a. NAME OF RESPONSIBLE INDIVIDUAL 22b. TELEPHONE (1ncddeAre. Code) 22c. OFFICE SYMBOL

Susan D. Monty, Publications Office (203) 449-3967 1

DD Form 1473, JUN 66 Previous editions ame obsoleft. SECURITY CLASSIFICATION OF THIS PAGE

S/N 0102-LF-014-6603 UNCLASSIFIED
UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS PAGE

Box 19. Cont.

on which the observer correctly declared the presence of a target), false alarm rates (percentage of trials on which the

observer incorrectly declared the presence of a target), and percentage of correct target identification (location) were

computed. Results showed that for the two strongest target levels, the four color coding schemes all produced

uniformly high performance. For the two weakest target levels, at a false alarm rate of 5"7, analyses of variance

showed that the color scheme specified by NUWC was superior to the other three in both hit rate and target

identification. This superiority became more evident as target strength (i.e., signal to noise ratio) decreased. This

color scheme uses highly saturated colors with the representation of signal intensity directly related to both luminance

and to the wavelength of the visible spectrum. Colorimetric specifications of the color schemes tested are provided.

DD Form 1473, JUN 86 (Reverie) SECURITY CLASSIFICATION OF THIS PAGE

UNCLASSIFIED