Chromaticity is an objective specification of the quality of acolor regardless of itsluminance. Chromaticity consists of twoindependent parameters, often specified ashue (h) andcolorfulness (s), where the latter is alternatively calledsaturation,chroma,intensity,[1] orexcitation purity.[2][3] This number of parameters follows fromtrichromacy of vision of most humans, which is assumed by most models incolor science.
In color science, thewhite point of an illuminant or of a display is a neutral reference characterized by a chromaticity; all other chromaticities may be defined in relation to this reference usingpolar coordinates. Thehue is the angular component, and thepurity is the radial component, normalized[clarification needed] by the maximum radius for that hue.
Purity is roughly equivalent to the termsaturation in theHSV color model. The propertyhue is as used in general color theory and in specificcolor models such asHSL and HSV color spaces, though it is moreperceptually uniform in color models such asMunsell,CIELAB orCIECAM02.
Somecolor spaces separate the three dimensions of color into oneluminance dimension and a pair of chromaticity dimensions. For example, the white point of ansRGB display is anx, y chromaticity of (0.3127, 0.3290), wherex andy coordinates are used in the xyY space.
These pairs determine a chromaticity asaffine coordinates on atriangle in a2D-space, which contains all possible chromaticities. Thesex andy are used because of simplicity of expression inCIE 1931 (see below) and have no inherent advantage. Othercoordinate systems on the same X-Y-Z triangle, or othercolor triangles, can be used.
On the other hand, some color spaces such asRGB andXYZ do not separate out chromaticity, but chromaticity is defined by amapping that normalizes out intensity, and its coordinates, such asr andg orx andy, can be calculated through thedivision operation, such asx = X/X +Y +Z, and so on.
The xyY space is a cross between the CIE XYZ and its normalized chromaticity coordinates xyz, such that the luminance Y is preserved and augmented with just the required two chromaticity dimensions.[4]
chromaticity hue saturation chroma colorfulness purity.
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