Tristimulus values defined

We finally arrive at the result we want, since we can now set up "Tristimulus Filters" to use in defining colors. We can now define "y as our standard luminosity curve for the human eye (photopic vision). Note that x, the red tristimulus value, has a certain amount of blue in it in order to duplicate the response of the red preceptor in the retina. 

In Eqs. (7)—(10), 5(A) is the spectral power distribution of the illuminant, and R A) is the spectral reflectance factor of the object. Jc(A), y(A), and 5(A) are the color-matching functions of the observer. In the usual practice, k is defined so that the tristimulus value, Y, for a perfect reflecting diffusor (the reference for R A)) equals 100. Using the functions proposed by the CIE in 1931, y(A) was made identical to the spectral photopic luminous efficiency function, and consequently its tristimulus value, Y, is a measure of the brightness of objects. The X and Z values describe aspects of color that permit identification with various spectral regions. 

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 ... 

The uniformity was assessed by selecting representative samples from the dyed lot and determining the color (tristimulus values) on a standard colorimeter (DIANO/LSCE Automate System). The difference in color of each specimen from the average color of all specimens was determined using the FMC II color difference formula (5J. In this system one unit of color difference is defined as the minimum perceptible difference in color. Thus spots or unlevel dyeing could be readily identified by variations in color difference between specimens from the same dyeing. 

The "tristimulus" variables X, Y, Z are defined by color-matching functions x(l), y(l), and z(l) (Fig. 10.4) that roughly correspond to the color sensitivity of the three types of human retina rods. For any "primary" color, with intensity 1(1), the tristimulus values X, Y, and Z are defined by... 

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... 

Color The color of the film can affect the consumer acceptance of coated produce (60). Five different color systems XYZ, Yxy, L a b, L C H° and Hunter Lab are used to express absolute chromaticity. Color system XYZ is measured as tristimulus values of color and forms the basis for most calculations. In the color system Yxy, Y is a lightness factor expressed as a percentage based on a perfect reflection of 100%. x and y are chromaticity coordinates defined by the following equations ... 

However, we find that these values are difficult to use since each color gives a set of tristimulus values, but each set does not have a specific relation to any other. The reason for this is that the intensity of Ir Ig 1b Therefore, we define a set of chromaticity coordinates where ... 

Luminous lu-m3-n9s [ME, fr. L luninosus, fr. lumin-, lumen] (15c) adj. (1) Adjective used to imply dependence on the spectral response characteristic of the Standard Observer defined in the CIE System. Thus, the luminous reflectance or the luminous transmittance is described by the Y-tristimulus value in the CIE System. The adjective is applied to many measures of light, such as... 

Reflectance, luminous n. Reflectance derived firom radiant flux by evaluating the radiant energy reflected according to its action upon a selective receptor (such as the eye), whose spectral sensitivity is defined by a standard relative luminous efficiency function. In popular usage, the term is used to describe the Y tristimulus value in the CIE system. 

The CIELUV formula is based on the chromatic scaling defined by this transformation combined with a scale of lightness. The system is related to a white reference object having tristimulus values, 7 , Z , with 7 , usually... 

The GIE Standard Observer. The CIE standard observer is a set of curves giving the tristimulus responses of an imaginary observer representing an average population for three primary colors arbitrarily chosen for convenience. The 1931 CIE standard observer was deterrnined for 2° foveal vision, while the later 1964 CIE supplementary standard observer appHes to a 10° vision a subscript 10 is usually used for the latter. The curves for both are given in Eigure 7 and the differences between the two observers can be seen in Table 2. The standard observers were defined in such a way that of the three primary responses x(X),jy(X), and X), the value ofjy(X) corresponds to the spectral photopic luminous efficiency, ie, to the perceived overall lightness of an object. 

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