TABLE OF CONTENTS The Commission Internationale de L' clairage (CIE) has defined a system that maps a spectral power distribution (SPD) of physics into a triple of numerical values-CIE XYZ tristimulus values that form the mathematical coordinates of color space. In this chapter, I describe the CIE system. In the following chapter, Color science for video, I will explain how these XYZ tristimulus values are related to linear-light RGB values.
Color coordinates are analogous to coordinates on a map (see Figure 21.1). Cartographers have different map projections for different functions: Some projections preserve areas, others show latitudes and longitudes as straight lines. No single map projection fills all the needs of all map users. There are many "color spaces" As in maps, no single coordinate system fills all of the needs of users.
| Note | For an approachable, nonmathematical introduction to color physics and perception, see Rossotti, Hazel, Colour: Why the World Isn't Grey (Princeton, N.J.: Princeton Univ. Press, 1983). |
In Chapter 20, Luminance and lightness, I introduced the linear-light quantity luminance. To reiterate, I use the term luminance and the symbol Y to refer to CIE luminance. I use the term luma and the symbol Y ? to refer to the video component that conveys an approximation to lightness. Most of the quantities in this chapter, and in the following chapter Color science for video, involve values that are proportional to intensity. In...
