In Color Science
Purity is roughly equivalent to the term "saturation" in the HSV color model. The property "hue" is as used in general color theory and in specific color models such as HSV or HSL, though it is more perceptually uniform in color models such as Munsell, CIELAB or CIECAM02.
Some color spaces separate the three dimensions of color into one luminance dimension and a pair of chromaticity dimensions. For example, the chromaticity coordinates are a* and b* in CIELAB, u and v in CIELUV, x and y in xyY space, etc. These pairs define chromaticity vectors in a rectangular 2-space, unlike the polar coordinates of hue angle and saturation that are used in HSV color space.
On the other hand, some color spaces such as RGB and XYZ do not separate out chromaticity; chromaticity coordinates such as r and g or x and y can be calculated by an operation that normalizes out intensity.
The xyY space is a cross between the CIEXYZ and its normalized chromaticity coordinates xyz, such that the luminance Y is preserved and augmented with just the required two chromaticity dimensions.
Read more about this topic: Chromaticity
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