Page 148 - Electrical Engineering Dictionary

but also the chrominance of pixels. See color resents luminance and C 1 and C 2 are color
blooming, chrominance, luminance. difference signals. The C 1 and C 2 signals are
then subsampled, but coded with the same
color coding the process of identifying algorithm as the Y signal. Standard algo-
components’ values and tolerances by means rithms do not attempt to exploit correlations
of a set of colored bands or dots. between the three signals.

color correction in practical photome- color matching the process of mixing
try it is known that the system used to mea- three fixed and independent primary colors
sure luminescence will not possess the stan- so that an observer (trichromat) interprets the
dard eye spectral response as specified by the formulation as being the same as a speci-
1931 International Commission on Illumina- fied but arbitrary color. In color television,
tion (CIE). The measurement “system” will the three primary colors are fixed at specific
undoubtedly consist of a photodetector, an wavelengths bands λ R , λ G , and λ B corre-
optical filter and associated lenses. Unfortu- sponding to colors red, green, and blue.
nately, system output is highly dependent on
its spectral response. color preference index (CPI) measure
appraising a light source for appreciative
color difference signals the chromi- viewing of colored objects or for promoting
nance signal component that results from an optimistic viewpoint by flattery.
subtracting the luminance (Y) component
from a primary color. The luminance sig- color representation a method of defin-
nal corresponds to the changes in brightness ing a signal or an image pixel value to be
as from a monochrome video signal. The associated with a color index.
three primary colors for color television sig-
nals are located in Maxwell’s chromaticity color saturation a color with the dom-
diagram. Red is at a wavelength of 0.7 mi- inant wavelength located at the periphery of
crometer, green at 0.546 micrometer and blue Maxwell’s chromaticity diagram. A fully
at 0.436 micrometer. The luminance signal saturated color is pure because it has not been
component results from the matrix addition contaminated by any other color or influence.
of the primary colors. The matrix propor-
tions are 30% red, 59% green, and 11% blue. color signal the portion of a modulated
Two color difference signals, (R-Y) and (B- signal that determines the colors of the in-
Y) are sufficient to convey all the information tended output display.
necessary to reproduce full color at the TV re-
ceiver. The color difference signal (G-Y) can color space the space C within which
be determined by proper proportions of the colors are represented in the image function
2
(R-Y), (B-Y) and Y signals at the receiver. I : R → C.

color graphics adapter (CGA) a video color temperature the color a black ob-
adapter proposed by IBM in 1981. It is ca- ject becomes when it is heated. The stan-
pable of emulating MDA. In graphic mode, dard color “white” occurs when a tungsten
it allows one to reach 640 × 200 (wide per filament is heated to a temperature of 6800
high) pixels with 2 colors or 320 × 200 with degrees Kelvin. The temperature of 6800 K
4 colors. corresponds to a standard white raster as de-
fined by the NTSC. The color temperature for
color image coding compression of color white is useful for comparing color match-
images is usually done by transforming RGB ing and color decoding among different dis-
color space into a YC 1 C 2 space, where Y rep- plays that use different color phosphors. The

c
2000 by CRC Press LLC