Chromaticity diagram
A chromaticity diagram plots color qualities such as hue and saturation independently of overall intensity, usually by normalizing tristimulus values.
CIE XYZ color space: A color space whose three tristimulus values represent color matches using nonnegative coordinates and a standardized reference white. The diagram’s familiar x and y coordinates are normalized from X, Y, and Z.
Color matching functions: Functions describing how much of each set of primary lights is needed to match monochromatic light at different wavelengths. They underpin the standard observer data from which chromaticity coordinates are derived.
Color gamut: The range of colors that a device, process, or color space can represent or reproduce. A device’s achievable colors appear as a bounded region in chromaticity coordinates.
CIE 1976 UCS: A CIE color space designed to make geometric distances between chromaticities more nearly uniform in perceived difference. Its u′v′ diagram improves on the uneven spacing of the traditional x,y diagram.
International Commission on Illumination: An international organization that develops standards for light, illumination, and color measurement. The CIE established the observer data and conventions used in standard chromaticity diagrams.
CIE xyY color space: A color representation that pairs CIE x and y chromaticity coordinates with luminance Y. It makes explicit that chromaticity and luminance are separate parts of a color description.
CIE standard observer: A standardized model of average human color-matching sensitivity, defined by the CIE for specified viewing conditions. Its color-matching functions make the diagram a standardized observer-based representation.
Gamut mapping: The process of transforming colors so they fit within the reproducible range of an output device or color space. Diagram geometry helps show which source colors must be altered for a target gamut.
CIE Lab color space: A perceptually organized color space with lightness and opponent-color axes, designed for color-difference comparisons. Unlike a basic chromaticity diagram, it includes lightness and aims for perceptual uniformity.
David MacAdam: An American color scientist known for research on color discrimination and chromaticity diagrams. His discrimination studies revealed that equal distances on the 1931 diagram do not mean equal perceived differences.