Three-dimensional color space

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 ... 

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... 

Figure 2.9. Three-dimensional color space (a) and color solid (b) of hue, lightness, and saturation (Minolta, 1993).

CIELAB An internationally accepted color space. CIE stands for Conjxnission Internationale de FEclairage. LAB stands for coordinates 1, a, and b, which are defined as mathematical coordinates in the three-dimensional color space. (Billmeyer, F. W. Saltzman, M. Principles of Color Technology , 2nd ed. Wiley New York, 1981 Chap. 2.)... 

A color can be numerically defined as a point in a three-dimensional color space. In the past, a vast number of color spaces, optimized for different applications have been developed. The most physical of these is the CIE-Yxy space, where all colors lie within a plane resembling a shoe sole. An arbitrary point B within that plane is defined by the Cartesian coordinates x and y, where the redness increases with x, and the greenness increases with y. The lightness, Y, is perpendicular to x and y out of the plane. An alternative... 

D Zmura and Lennie assume that red-green as well as blue-yellow color opponent cells are used to arrive at stable hue descriptors. They represent the chromatic sensitivity of a cell using a three-dimensional chromaticity space as shown in Figure 8.10. The white point is denoted by W. The white point describes the steady state of adaptation of the cell. The vector C represents the most effective choice of chromatic contrast, which will activate the cell. The preferred hue of the cell can be found by projecting the vector C onto... 

Figure 8.10 Three-dimensional chromaticity space of a color cell. (Reproduced from D Zmura M and Lennie P 1986. Mechanisms of color constancy. Journal of the Optical Society of America A, 3(10), 1662-1672, by permission from The Optical Society of America.)...

This transformation results in a three-dimensional space that follows the opponent color system with +a as red, —a as green, +5 as yellow, and — b as blue. CIELAB is closely related to the older Adams-Nickerson, modified Adams-Nickerson, and other spaces of the Y,a,b type, which it replaced (1,3). 

In the CIELAB and CIELUV color spaces, the difference between a batch sample and a reference standard designated with a subscript s, can be designated by its components, eg, AAL = L — L. The three-dimensional total color differences are given by EucHdian geometry as the 1976 CIE lYa b and 1976 CIE lYu Y color difference formulas ... 

The HunterLab system (1958) was the hrst to use the opponent color theory stating that the red, green, and blue cone responses are re-mixed into opponent coders as they move up the optic nerve to the brain.Based on that theory, the HunterLab color space is three-dimensional and rectangular (see Figure 1.6). 

Ultramarines are three-dimensional cage-like structures. They differ from feldspars and zeolites because of the large spaces within the structures that can contain cations and anions but not water, illustrating a natural buckeyball-like structure and cavity, and a diversity of environment between the internal and external cages. Ultramarines can act as ion-exchangers for both anions and cations. The blue color of ultramarines is due to the presence of the ion although a yellow ion S2 also exists in the same structure. 

In the work with cottonseed flours, we used the Hunterlab color meter D25D2A and expressed these measurements as Hunter L, a, b color values. These are coordinates of the three-dimensional opponent-color space shown in Figure 2. The L value measures lightness, or the amount of light reflected or transmitted by the object. The a and b values are the chromaticity coordinates from which information about hue and saturation can be obtained. The a value measures redness when plus and greenness when minus. The b value measures yellowness when plus and blueness when minus. 

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