Chromaticity

Chromaticity consists of two independent parameters, often specified as hue (h) and colorfulness (s), where the latter is alternatively called saturation, chroma, intensity,[1] or excitation purity.

[2][3] This number of parameters follows from trichromacy of vision of most humans, which is assumed by most models in color science.

In color science, the white 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 using polar coordinates.

Purity is roughly equivalent to the term saturation in the HSV color model.

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.

The CIE 1931 xy chromaticity space, also showing the chromaticities of black-body light sources of various temperatures, and lines of constant correlated color temperature
sRGB gamut plotted in xyY color space (chromaticity + luminosity)
( u′ , v′ ) , the chromaticity in CIELUV , is a fairly perceptually uniform presentation of the chromaticity as (another than in CIE 1931) planar Euclidean shape. This presentation is a projective transformation of the CIE 1931 chromaticity diagram above.