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A-2 Desktop Color Primer
The mixture of light wavelengths emitted by a light source is reflected
selectively by different objects. Different mixtures of reflected light appear as
different colors. Some of these mixtures appear as relatively saturated colors,
but most appear to us as grays or impure hues of a color.
CIE color model
In the 1930s, the Commission Internationale de l’Eclairage (CIE) defined a
standard color space, a way of defining colors in mathematical terms, to help
in the communication of color information. This color space is based on
research on the nature of color perception. The CIE chromaticity diagram
(plate 2) is a two-dimensional model of color vision. The arc around the top
of the horseshoe encompasses the pure, or spectral, colors from blue-violet to
red. Although the CIE chromaticity diagram is not perceptually uniform—
some areas of the diagram seem to compress color differences relative to
others—it is a good tool for illustrating some interesting aspects of color
vision.
By mixing any two spectral colors in different proportions, we can create all
the colors found on the straight line drawn between them in the diagram. It
is possible to create the same gray by mixing blue-green and red light or by
mixing yellow-green and blue-violet light. This is possible because of a
phenomenon peculiar to color vision called metamerism. The eye does not
distinguish individual wavelengths of light. Therefore, different combinations
of spectral light can produce the same perceived color.
Purple colors, which do not exist in the spectrum of pure light, are found at
the bottom of the diagram. Purples are mixtures of red and blue light—the
opposite ends of the spectrum.
Hue, saturation, and brightness
A color can be described in terms of three varying characteristics, called the
HSB color model:
• Hue—tint (the qualitative aspect of a color—red, green, or orange)
• Saturation—the purity of the color
• Brightness—relative position between white and black.
While the CIE chromaticity diagram (plate 2) conveys hue and saturation, a
three-dimensional color model is required to add the brightness component
(plate 3).