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The spectrum of a standard illuminant, like any other profile of light, can be converted into tristimulus values. The set of three tristimulus coordinates of an illuminant is called a white point. If the profile is normalized, then the white point can equivalently be expressed as a pair of chromaticity coordinates.
An illuminant is characterized by its relative spectral power distribution (SPD). The white point of an illuminant is the chromaticity of a white object under the illuminant, and can be specified by chromaticity coordinates, such as the x, y coordinates on the CIE 1931 chromaticity diagram (hence the use of the relative SPD and not the absolute SPD, because the white point is only related to ...
The color swatches represent the color of each white point, ... light white fluorescent F7 0.31292: 0.32933 0.31569: 0.32960 6500 D65 simulator, daylight simulator F8
where , , and are the color-balanced tristimulus values; , , and are the tristimulus values of the viewing illuminant (the white point to which the image is being transformed to conform to); ′, ′, and ′ are the tristimulus values of an object believed to be white in the un-color-balanced image, and ′, ′, and ′ are the tristimulus ...
The white point is generally defined as—or assumed to be—equal energy white (illuminant E). This is defined as [x, y] = (1/3, 1/3) in CIE xyY , and as [X, Y, Z] = (1, 1, 1) in XYZ color space . However, other white points may be used, generally defined by "white" standard illuminants or a color temperature such as 6500 K (D65).
For example, the white point of an sRGB display is an x, y chromaticity of (0.3127, 0.3290), where x and y coordinates are used in the xyY space. (u′, v′), the chromaticity in CIELUV, is a fairly perceptually uniform presentation of the chromaticity as (another than in CIE 1931) planar Euclidean shape.
The mathematical procedure for determining the correlated color temperature involves finding the closest point to the light source's white point on the Planckian locus. Since the CIE's 1959 meeting in Brussels, the Planckian locus has been computed using the CIE 1960 color space, also known as MacAdam's (u,v) diagram. [6]
The elements of the diagonal matrix D are the ratios of the cone responses (Long, Medium, Short) for the illuminant's white point. The more complete von Kries transform, for colors represented in XYZ or RGB color space, includes matrix transformations into and out of LMS space, with the diagonal transform D in the middle. [6]