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Chapter 11 ∣ Color
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the color-independent component, brightness
(Munsell’s value), from hue and saturation
(Munsell’s chroma). This enables two-dimensional
color representation. In addition, it is perceptually
uniform. Color distances on the model correspond
to perceived differences between the colors. Every
color has a specific location with this system.
While this may be an effective method of definition
when dealing with pigments, working with and
reproducing colors digitally requires a much more
scientific and consistent system.
The International Commission
on Illumination (CIE)
To precisely match colors in the graphic
communications industry, most ink and paper
manufacturers have adopted the CIE system of
color specification. CIE stands for Commission
Internationale de l’Eclairage, or the International
Commission on Illumination. In 1931, the CIE
established a worldwide color measurement
standard. The CIE system is a mathematical model
of human color perception, Figure 11-16. Numerical
values quantify the responses of the average
human eye to different wavelengths of light.
The CIE defined several standard light sources, a
standard observer, and standard viewing conditions.
See Figure 11-17. The standard observer was
chosen to have color vision representing that of
the average person. Standard viewing conditions
were determined using a dark background and only
foveal vision. Foveal vision covers only about a 2°
angle of vision. The CIE’s angle of vision is 10°. The
wider angle provides a more accurate correlation
with the visual perception for larger samples.
The CIE Uniform Color Space (CIE XYZ)
Determining accurate color measurements
requires information from three variables: the light
source, the color sample, and the receiver. After
this information is gathered, a sample’s tristimulus
values (X, Y, Z) can be determined. The X, Y, and Z
stand for red, green, and blue (RGB), respectively.
Any color may be specified on the CIE XYZ color
model by listing the amounts of the three primary
colors (red, green, and blue) required to match it.
Certain methods are used to manipulate the data
graphically or mathematically. These values can be
quickly determined using measurement devices,
computers, and computer software.
The CIE XYZ color space is the parent system
for nearly all color standards. Variations such as the
CIE Yxy, CIELAB, and CIE Luminance Y models
serve different scientific and technical purposes.
The CIE Chromaticity Diagram
The CIE chromaticity diagram (CIE Yxy color
space) is a two-dimensional graph of hue and
chroma, Figure 11-18A. Chromaticity refers to a y
quality of color that includes hue and saturation, but
not brightness.
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Figure 11-17. The CIE Standard Illuminants. D65 is the most
widely used to represent average daylight conditions. D55
and D50 are other commonly used daylight sources.
Illuminant Temperature
CIE source A, tungsten 2856 K
CIE source B, sunlight 4870 K
CIE source C, daylight 6770 K
CIE source D50, daylight 5000 K
CIE source D55, daylight 5500 K
CIE source D65,
daylight
6500 K
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Figure 11-16. Responses of the average human eye to different
light waves were used to establish the CIE color standard. As
illustrated above, the human eye does not perceive color as
equally spaced. Human perception of color is much greater
in the center of the spectrum than on the ends.
Reflective
Output
Wavelength (nm) 38D
D
78D