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Graphic Communications
Copyright Goodheart-Willcox Co., Inc.
As with Munsell’s HVC color model, the CIE
Yxy separates the achromatic component (Y) from
the two chromatic components (xy). Two colors
that are the same except for luminance would have
the same chromatic definition, and therefore the
same chromaticity coordinates. The chromaticity
coordinates are represented by the x and y values.
The color’s brightness (Y) is specified by a number,
not a location on the graph, Figure 11-18B.
The CIE chromaticity diagram has a horizontal
x axis and a vertical y axis. When the chromaticity
coordinates of visible light (380 nm–770 nm) are
converted and plotted, the resulting points fall on a
horseshoe-shaped curve known as the spectrum
locus, Figure 11-19A. Since all visible colors
are comprised of mixtures of light wavelengths,
all visible colors must occur within the boundary
Goodheart-Willcox Publisher
Figure 11-18. A—The CIE chromaticity diagram represents
the hue and saturation of a specific color or the chromaticity
coordinates of that color. B—The luminance value (Y) is seen
as a vertical axis, rising up from a neutral position of the
illuminant or light source.
Saturation
A
Hue
Y
X
x
0%
C
y
Y
100%
B
Thomas Detrie
Figure 11-19. A—The CIE chromaticity chart. B—The bold
line between 380 nm and 770 nm represents the purple
boundary at the base of the spectrum locus.
A
Purple
line
520
B