Different color-imaging devices use different color spaces; well-known examples are the RGB space of televisions and cmy (or cmyk) space of printers. Colors produced by these devices are device specific, depending on the characteristics of the device. To ensure a proper color rendition in various devices, a device-independent color space, such as CIE color spaces using colorimetry to give a quantitative measure for all colors, is needed to serve as a reliable interchange standard. CIE color spaces are the colorimetric spaces that are device-independent. The nucleus of the CIE color space is the tristimulus values or CIEXYZ space that is discussed in Chapter 1. In this chapter, we present derivatives and modifications of the CIEXYZ space and the related topics of the gamut boundary, color appearance model, and spatial domain extension.
5.1 CIE 1931 Chromaticity Coordinates
Chromaticity coordinates are the normalization of the tristimulus values X, Y, and Z; they are the projection of the tristimulus space to the 2D x-y plane. Mathematically, they are expressed as x=Xâ(X+Y+Z), y=Yâ(X+Y+Z), z=Zâ(X+Y+Z), and x+y+z=1, where x, y, and z are the chromaticity coordinates.
5.1.1 Color gamut boundary of CIEXYZ
The color gamut boundary in CIEXYZ space is well defined in chromaticity diagrams as the spectrum locus enclosed by spectral stimuli.
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