CIE XYZ Color Space

Using these sensitivities, we can calculate the luminous flux of any light source (International Commission on Illumination 1983 Jahne 2002). Let f (/,) be the radiant flux at wavelength X of the light source. Let V (X) be the sensitivity of scotopic vision and V(X) be the sensitivity of photopic vision, then the intensity of the light source is 

After the linear transformation has been applied, the weights x, y. and z are computed as follows  

Tristimulus values X, Y, and Z are computed for a primary light source with power spectrum L(X) from the color-matching functions x, y, and z as follows  

Here R(k) denotes the reflectance of the object. In this case, the constant k is set to 

If the energy of each primary color is increased by the same percentage, then the relative responses of the receptors will not be any different. Therefore, colors are usually specified using normalized colors, or chromaticities. The chromaticities of the CIE color space are given by 

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In 1976, the CIE defined a three-dimensional color space that is perceptually more uniform than the CIE XYZ color space (International Commission on Illumination 1996). The... 

Since 1931, the most widespread color spaces for colorimetry of luminescent materials are based on the CIE XYZ color space. The CIE (commission intemationale de I eclairage) is an organization that standardizes all the color sciences. Here, X, Y, and Z coordinates represent a defined combination of R, G, and B so that the sensitivity function that defines the Y coordinate fits the photopic sensitivity of the eye (average sensitivity function of the... 

Figure 4.7 Gamut of colors in CIE XYZ space. The chromaticities of light in the visible range from 400 nm to 700 nm form a horseshoe-shaped region. The chromaticities for a black-body radiator at different temperatures is shown in the center. The color of a black-body radiator passes from red at low temperatures through white and on to blue at higher temperatures. The point of equal energy is located at the center of the graph.

By creating scales for hue, lightness, and chroma, we can now measure color numerically. Other methods for expressing color numerically were developed by the Commission Internationale de l Eclairage (CIE), an international organization concerned with light and color. The two most widely known of these methods are the Yxy color space, devised based on tristimulus values XYZ defined by CIE, and... 

Subsequent to determining standard and lot tristimulus XYZ values, one simply plugs those calculated values into the CIE Lab color equations. Why the CIE system Because CMC uses the DLab values, generated in CIE color space, to determine DC, DH, and eventually CMC DE. 

Chromaticity diagram A 2D plot of the chromaticity values X and y derived from the tristimulus values XYZ. A plot of CIE color space. 

Tristimulus values Three values (XYZ) calculated using a spectrum in the visible range, standard illumirrate values, and weighting factors associated with the CIE color space system. 

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