Trichromatic, defined

Colorimetry [1.17] - [1.19]. The principles of colorimetry are based on the fact that all color stimuli can be simulated by additively mixing only three selected color stimuli (trichromatic principle). A color stimulus can, however, also be produced by mixing the spectral colors. Thus, it has a spectral distribution, which in the case of nonluminous, perceived colors is called the spectral reflectance q (2). After defining three reference stimuli, the trichromatic principle allows a three-dimensional color space to be built up in which the color coordinates (tristimulus values) can be interpreted as components of a vector (CIE system for standards, see Table 1, Colorimetry CIE = Commission Internationale de l Eclairage). For uncolored illumination the three CIE tristimulus values depend on the spectral reflectance as follows ... 

Thus, a color is characterized by three numbers, X, Y, and Z, and, consequently, can be shown as a point in a three-dimensional coordinate system. Since each kind of color may be defined by its color proportion, or what is known as the standard color value proportion (trichromatic coefficient), and, by definition, the sum of all the trichromatic coefficients is unity, then, the color can be shown as a point in a two-dimensional diagram. This diagram is also known as the chromaticity diagram or color table (Figure 14-8). The line joining the points at 400 and 700 nm is called the purple line. Thus, all real colors lie within the horseshoe structure in Figure 14-8. 

Trichromat tri-kro- mat [back-formation fir. trichromatic] (1929) n. Person requiring mixtures of three component primaries to match colors. Normal observers fall into this classification the CIE standard observer is defined in terms of the amounts of three primary colors required to match all spectral colors. Not all trichromats are normal, however. Some observers exhibit anomalous trichromatism, requiring abnormal proportions of three primary colors for color matching. 

Five important treatises on color have appeared in recent years. Handbook of Colorimetry (Hardy, 1936) is a direct outcome of the eighth session of the International Commission on Illumination in 1931. It enables us to compute psychophysical values for brightness (later termed luminous refiectance and now, lightness) and chromaticity (dominant wave length and purity) from the raw spectrophotometric data. In these psychophysical terms, a colored sample may be uniquely defined with respect to its color, provided that we follow a standard procedure for determining the spectral refiectance or transmittance of the sample. The perceived color, however, is not defined, and we enter here into psychological considerations as distinct from those of psychophysics. The C.I.E. quantities x and y (the trichromatic coefficients which... 

---