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The CIELAB color space, also referred to as L*a*b*, is a color space defined by the International Commission on Illumination (abbreviated CIE) in 1976. [ a ] It expresses color as three values: L* for perceptual lightness and a* and b* for the four unique colors of human vision: red, green, blue and yellow.
The CIE 1976 color difference formula is the first formula that related a measured color difference to a known set of CIELAB coordinates. This formula has been succeeded by the 1994 and 2000 formulas because the CIELAB space turned out to be not as perceptually uniform as intended, especially in the saturated regions.
The CIE 1931 colour space chromaticity diagram with wavelengths in nanometers.The colors depicted depend on the color space of the device on which the image is viewed.. The International Commission on Illumination (usually abbreviated CIE for its French name Commission internationale de l'éclairage) is the international authority on light, illumination, colour, and colour spaces.
CIELAB produces a color space that is more perceptually linear than other color spaces. Perceptually linear means that a change of the same amount in a color value should produce a change of about the same visual importance. CIELAB has almost entirely replaced an alternative related Lab color space called “Hunter Lab”. This space is ...
It includes CIE standard tristimulus colorimetry and transformations to a number of non-linear color appearance models (CIELAB, CIECAM, etc.). Excel spreadsheet with forward and inverse examples Archived 2007-01-09 at the Wayback Machine , by Eric Walowit and Grit O'Brien
Helmholtz–Kohlrausch effect has been described in mathematical models by Fairchild and Pirrotta 1991, Nayatani 1997, and most recently High, Green, and Nussbamm 2023. Given a color's CIELAB coordinates, these methods produce an adjusted "equivalent achromatic lightness" L* EAL, i.e. the shade of grey humans think is as bright as the color. [5]
For example, the color white is a bright color, while the color grey is considered to be a less bright version of that same white. In other words, the chromaticity of white and grey are the same while their brightness differs. The CIE XYZ color space was deliberately designed so that the Y parameter is also a measure of the luminance of a color.
When defining a color space, the usual reference standard is the CIELAB or CIEXYZ color spaces, which were specifically designed to encompass all colors the average human can see. [1] Since "color space" identifies a particular combination of the color model and the mapping function, the word is often used informally to identify a color model.