FIGURE 2.5 Color reflectance curves. Each color is characterized by its spectral reflectance curve.

the standard observer must be a representative element of the human population, with normal color vision who must generate three coordinates that match a corresponding color. Basically, the standard observer evaluates the color produced on a white screen. The screen is illuminated by light from one or more of the three lamps. The experiment is designed to give light of three widely different colors, that is, the primary colors red, green, and blue. Light intensity is adjusted by the observer to get the mixture of the three colors that matches that of a test lamp of the desired color (x, y, z). These three lamps are characterized by their independent wavelength functions (color-matching functions). Figure 2.8 shows the corresponding color-matching functions (x, y, z ) for one of the standard observers defined by the CIE (2° CIE observer). Standard observers are averages, or composites, based on experiments with a small number of people (15 to 20) with normal color vision. The 2° number is associated with the vision angle and corresponds to the region of the

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