DTIC ADA258770: Reproduction of Custom Colors for the Navy's Compressed Aeronautical Chart

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•" Iz. Report Date. 3. Report Type and Dates Covered./
4. Title and Subtitle. 5. Funding Numbers.
Reproduction of Custom Colors for the Navys' Compressed Aeronautical Chart Contract
Program Element No. 0604262N
6. Author(s). Project No. 64214
Stephanie A. Myrick, Maura C. Lohrenz, and Perry B. Wischow Task No.
Accession No. tN257017
Work Unit No. '5312F
7. Performing Organization Name(s) and Address(es). 8. Performing Organization
Naval Research Laboratory Report Number.
Ocean Science Directorate PR 92:054:351
Stennis Space Center, MS 39529-5004
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Naval Air Systems Command Report Number.
Department of the Navy (AIR-803)
Washington, DC 20361-8030 PR 92:054:351
11. Supplementary Notes.
Published in IS&T's Eighth International Congress on Advances in Non-Impact Printing Technologies.
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Approved for public release; distribution is unlimited.
13. Abstract (Maximum 200 words).
This paper presents a procedure that is used to reproduce custom colors on color hardcopy. The set of custom colors is comprised
of red, green, and blue (RGB) intensities, where intensity levels range from 0 (no intensity) to 255 (maximum intensity). The hardcopy
device that produced the results in this paper normally transforms RGB colors into cyan, magenta, yellow, and black (CMYK).
However, adding black ink during the printing process tends to cause the loss of some low-intensity colors and an overall graying
of the output image. This phenomenon has been termed "color drop-out." The procedure described in this paper eliminates color
drop-out in custom color reproduction by omitting black ink. This approach more accurately reproduced custom colors for the data
set used in this study. Two other less successful methods are also presented.
DTIC
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DEC 10 .i
14. Subject Terms. 15. Number of Pages.
Digital maps, optical storage, databases, data compression
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IS&T Final Program and Proceedings
IS&T's Eighth International Congress on
Advances in Non-Impact
Printing Technologies
October 25 - 30, 1992
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92 12 09 038
REPRODUCTION OF CUSTOM COLORS FOR
THE NAVY'S COMPRESSED AERONAUTICAL CHART
StephanieA . Myrick, Maura C. Lohrenz, and PerryB . Wischow, Naval Research Laboratory Detachment, Stennis Space Center, MS
ABSTRACT CAC RGB intensities are normalized for use with conven-
tional display devices by using the following algorithm:
This paper presents a procedure that is used to reproduce
custom colors on color hardcopy. The set of custom colors is R = R/255.0
wmrprised of red, green and blue (RGB) intensities, where G = G/255.0 (1)
intensity levels range from 0 (no intensity) to 255 (maximum B = B/255.0.
intensity). The hardcopy device that produced the results in
this paper normally transforms RGB colors into cyan, magenta, The in-house plotter plots CAC data by first converting the
yellow, and black (CMYK). However, addingblackinkdturing normalized CAC RGB intensities to their CMY equivalents.
the printing process tends to cause the loss of some low- The following transformation2 is used for converting from
intersity colors and an overall graying of the output image. RGB to CMY:
This phenomenon has been termed "color drop-out." The
[IAGI
procedure described in this paper eliminates color drop-out in [C 1 I R
custom color reproduction by omitting black ink. This ap- (2)
"U- proach more accurately reproduced custom colors for the data
set used in this study. Two other less successful methods are
16 also presented. r
INTRODUCsION CMY values are adjusted to reflect the plotter's addition of
black ink. The adjustment algorithm2 uses black in place of
: The Navy is developing a database of scanned aeronauti- equal amounts of CMY as follows:
cal chart images, the Compressed Aeronautical Chart (CAC),
for use in aircraft digital moving-map systems and for mission K = minimu (C,M,Y)
planning.1 The CAC usesasetof30customcolor palettes. Each C = C -K (3)
palette consists of 240 distinct colors, and each color is coin- M M -K
S prised of RGB intensities. Intensity levels range from 0 (no Y =Y -K.
intensity) to 255 (maximum intensity). Although the CAC is
primarily destined for video display, the need for high-resolu- Using a 4 x 4 pixel pattern, CMYK inks are deposited on
tion color hardcopies also exists. Available plotter hardware paperasagrid of colored dots. Theorientationofeachcolored
and software produced unacceptable colors, since the low dot allows the eye to spatially integrate light that is reflected
intensities of certain CAC palette colors resulted in poor color from adjacent dots. For any given CMYK component, a 7%
reproduction in hardcopy. Low-intensity palette colors suf- minimum intensity is required to have at least 1 element
fered from color drop-out, which tends to produce colors with activated, out of 16 in the pixel matrix. CMYK components
a gray-shade appearance. It was discovered that color drop- with intensities of less than 7% (i.e., no color) will not be
out is caused byaddition of black ink, which is specified by the plotted. The following algorithm3 is used to calculate the
plotter software. Some color hardcopy devices produce black number of elements (within the matrix) to activate for a given
by blending the three primary inks (RGB or cyan, magenta, CMYK intensity:
yellow (CMY)). However, this process often results in a
somewhat muddy black. This problem has been solved for Numberofelements = (intensity * matrix size) /100 (4)
other devices by using black ink to produce true blacL .These
devices also add black ink to colors other than true blackwhich, where intensity = (intensity * 100) + 0.5
when combined with the subsequent reduction in the CMY matrix size = 4 x 4 elements.
intensities for those colors, can produce the graying effect of
color drop-out. The CAC palette has been sorted by increasing intensity.
This paper presents a procedure that eliminates color AsshowninFig. 1,colordrop-outwas mostsevere;in the lower
drop-out and reproduces custom CAC palette colors that are intensities. One attempt to alleviate color drop-out was based
comparable in quality to the colors found in original aeronau- on the hue, lightness, saturation (HLS) color model,2 in which
tical charts. the CAC color palette was shifted toward white along the
achromatic axis to increase the overall color palette intensities
PROBLEM DESCRIPTION (Fig. 2). This achromatic shift succeeded in producing less
color drop-out in lower intensity colors. However, the shift
The custom color palettes for CAC data are based on resulted in the opposite problem: lighter intensity colors were
intensities of the additive primary colors: RGB. The in-house, "washed out" (i.e., too much white). Applying a combination
high-resolution, color plotter hardware, which relies on the of achromatic shifts to individual colors was deemed undesir-
complementary subtractive primary colors, CMY, produced able due to the significant number of color palettes that would
plots with unacceptable colors. In particular, the lower inten- have to be modified. Even with the availability of examples of
sity colors suffered from color drop-out which, as previously computer-generated colors,4 where percentages of eachCMYK
described, resulted inagray-shadeappearance (Fig.1 ). Higher ink are provided, there are simply too many individual CAC
intensity colors suffered less trom color drop-cut but still did palette colors that would have to be matched.
not reproduce well.
IS&T's Eighth InternationalC ongress on Advrranas in Non-Impact PrintingT echnologies (1992)-463
Another attempt to alleviate color drop-out involved in- approximated by blending CMY colors, the use of black ink
creasing the pixel pattern to 8 x 8. The procedure required, a was completely eliminated. Test plots revealed that the
minimum intensityof 2% foranygiven CMYK color to have at deletion of black ink from the RGB to CMYK transformation
least 1 element activated out of 64. This attemptalso proved to resulted in the successful reproduction of all CAC custom
be unsatisfactory because although the resulting plots had less colors.
color drop-out, they suffered a gridded appearance due to the An interesting corollary to this study was the demon-
orientation of colored dots within the matrix. strated vulnerability of plot quality to environmental and
An underlying problem with both of these approaches is chemical factors. The quality of plot appearance was pro-
the large number of colors that requires manipulation (240 foundly influenced by environmental factors, such as room
colors in each of the 30 standard CAC color palettes). Rather temperature and humidity. Chemical factors relating to the
than working with every color in a given palette, a test palette toner and replenisher (i.e., age and percentage used) also
was devised. Since CAC data is comprised of RGB intensities affected plot quality. The adverse influence of these factors
(which are later transformed into their CMYK components), was manifested by uneven distribution and absorption of ink
various intensities of RGB were selected as test colors. The Due to the significant influence of environmental and chemical
colors' intensities were chosen to vary in lightness by 12%, from factors on plot quality and appearance, reference plots are now
little to full pure color. Fig. 3 presents a plot of these colors and optional on all in-house plotter output. These reference plots,
shows how adding black ink influences the appearance of the which include smaller versions of the RGB and color palette
resultant RGB colors. Except in the case of colors with full plots, help identify whether a poor plot was due to color
intensity (e.g., pure red, pure green, or pure blue), black ink is problems or to environmental/chemical influences.
always noticeably present. ACKNOWLEDGMENTS
,SOLUTION DESCRIPTION
This work resulted from ongoing efforts within the Naval
Although CACcolor palettes contain true black, true black Research Laboratory's Map Data Formatting Facility (MDFF).
is rarely found in the digitized aeronautical charts. It is present The MDFF is funded by the Naval Air Systems Command
in CAC palettes primarily for areas of no data coverage. Since (NAVAIR) F/A-18 (program element APN), and V-22 (pro-
the CAC data rarely (if ever) require true black, and since the gram element 64262) programs. The authors thank the follow-
addition of black by the plotter seriously compromises the ing program managers at NAVAIR for their support: CDR V.
qualityof manyother CACcolors, the final solution to the color J. Chenevy, LCDR C. Cleaver, and MajorJ. P. Stevens (F/ A-1 8);
drop-out problem pivoted around the elimination of black ink and CDR M. Redshaw (V-22). NOARL contribution number
from the plotting process. PR92.154:351.
The FORTRAN source code for the plotter software3 was
modified in-house to completely omit the inclusion of black REFERENCES
ink- RGB intensities were converted to their CMY equivalents 1. Nt C. Lohrenzand J.E .R yan,TheNavy Standard Comprsed
(Eq. 2), and the adjustment algorithm (Eq. 3) for black ink was Aeronautical Chart Database, Naval Research Laboratory, Re-
eliminated. Fig. 4 presents the resulting test plot of RGB colors port 8 (July 1990).
(in which intensity varies by 12% from little to pure color) using 2. J.D. FoleyA. van Dam,S. K. Feiner,andJ. F.H ughes, Comrputer
CMY inks and no black ink. The lower intensity RGB colors, Graphics: Principles and Practice, Addison-Wesley, Reading,
which were particularly susceptible to color drop-out, are MA, 1990, pp. 588-594.
acceptable in appearance. The higher intensity RGB colors are 3. COLRGN, CalComp Inc., Anaheim, CA.
also acceptable. Using the modified plotter software, another 4. M.R ogondino and P. Rogondino, Computer Color: 10,000 rac-
puter-generatedp rocess colors, Chronicle Books, San Francisco,
custom color palette plot was created. As shown inFig. 5, the CA, 1990.
palette suffered no appreciable color drop-out, and all colors
were more accurately reproduced. 1.0 Whit
CONCLUSIONS AND`ECOMMENDATIONS "
Results from the color experiments documented here indi-
cate that the addition of black ink interferes with the reproduc-
tion of custom colors on some hardcopy plotters. The Navy
standard CAC database was used in this study. CAC data use G Y~
a standard set of 30 custom-designed color palettes, each of
which consists of 240 RGB colors. The custom RGB colors in 0.5 Red
CAC data did not reproduce well on an in-house, CMYK- cyanJ 0"
based, color hardcopy device that added black ink during the
RGB to CMYK transformation. In particular, the addition of Ien
black ink resulted in a graying effect, termed color dyop-out, in
most CAC colors. Several adjustments were considered,
including a shift of the colors along the achromaticaxis (toward
higher overall intensities), increasing the size of the pixel
pattern matrix from 4 x 4 to 8 x 8 pixels, and eliminating the
inclusion of black ink. The first two approaches did not s
adequately solve the color reproduction problems; the third Blac
app(cid:127)uach proved to be the best solution. Since true black is
rarely needed by the CAC database, and since black can Figure 2. HLS color model.
464-IS&T's Eighth International Congress on Advances in Non-impact PrintingT echnologies (1992)
Figure 3. RGB test plot using
CMYK inks.
S1
Figure 1. CAC custom color palette with color
drop-out.
Figure 4. RGB test plot using CNIY
inks and no black (k) ink.
.14.
I ieurc 5. A CACculwciOo lor palcite \\ilhtl colo,
dloll-Out.