CIE 1931 color space

A color space defined by the CIE 1931 standard observer and color-matching functions, representing colors with tristimulus values X, Y, and Z. Its XYZ coordinates encode color matches independently of a particular display’s primaries.

CIE 1931 standard observer: A standardized model of average human color-matching responses, defined by the CIE in 1931. Its color-matching functions are the basis for the XYZ tristimulus system.
Color matching: The process of adjusting light sources until their perceived colors match. The XYZ system formalizes matches made by the CIE standard observer.
CIE xyY color space: A color representation using chromaticity coordinates x and y together with luminance Y. It repackages XYZ into separate chromaticity and luminance coordinates for practical use.
RGB color model: A color model that represents colors as combinations of red, green, and blue primaries. Unlike XYZ, RGB coordinates depend on specified primaries and a device or encoding.
CIE color-matching functions: Functions that specify the amounts of three primaries needed to match monochromatic lights for a standard observer. They transform a light’s spectral power distribution into the X, Y, and Z values.
Metamerism: The phenomenon in which different spectral distributions produce the same perceived color under specified viewing conditions. Different spectra can yield identical XYZ values when they match for the standard observer.
CIE Lab color space: A perceptually organized color space with lightness and opponent-color axes, defined relative to a reference white. Its coordinates are calculated from XYZ and are designed to make color differences more uniform.
sRGB: A standardized RGB color space designed for common displays and digital imaging. Its bounded display gamut contrasts with XYZ’s role as a reference color space.
Tristimulus values: Three numerical quantities that specify a color match for a given observer and set of matching functions. XYZ is a particular tristimulus system derived from the 1931 functions.
CIE standard illuminant: A defined spectral power distribution used as a reference light source in colorimetry. XYZ measurements for reflecting objects depend on the illuminant used to calculate their stimulus.

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