Ricoh AP3850C Service Manual download pdf (Page 166)

A-2 Desktop Color Primer

Like the sun, most light sources we encounter in our daily environment emit a mixture

of light wavelengths, although the particular distribution of wavelengths can vary

considerably. Light from a tungsten light bulb, for example, contains much less blue

light than sunlight. Tungsten light appears white to the human eye, which, up to a

point, can adjust to the different light sources. However, color objects appear different

under tungsten light than they do in sunlight because of the different spectral makeup

of the two light sources.

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 (color example 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.

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Ricoh AP3850C Service Manual Page 166