Incolorimetry, theCIE 1976L*,u*,v*color space, commonly known by its abbreviationCIELUV, is acolor space adopted by theInternational Commission on Illumination (CIE) in 1976, as a simple-to-compute transformation of the 1931CIE XYZ color space, but which attemptedperceptual uniformity. It is extensively used for applications such as computer graphics which deal with colored lights. Although additive mixtures of different colored lights will fall on a line in CIELUV's uniformchromaticity diagram (called theCIE 1976 UCS), such additive mixtures will not, contrary to popular belief, fall along a line in the CIELUV color space unless the mixtures are constant inlightness.

CIELUV is anAdams chromatic valence color space and is an update of theCIE 1964 (U*,V*,W*) color space (CIEUVW). The differences include a slightly modifiedlightness scale and a modified uniform chromaticity scale, in which one of the coordinates,v′, is 1.5 times as large asv in its1960 predecessor. CIELUV andCIELAB were adopted simultaneously by the CIE when no clear consensus could be formed behind only one or the other of these two color spaces.

CIELUV uses Judd-type (translational)white point adaptation (in contrast with CIELAB, which uses avon Kries transform).^[1] This can produce useful results when working with a single illuminant, but can predictimaginary colors (i.e., outside thespectral locus) when attempting to use it as achromatic adaptation transform.^[2] The translational adaptation transform used in CIELUV has also been shown to perform poorly in predicting corresponding colors.^[3]

By definition,0 ≤L* ≤ 100.

CIELUV is based on CIEUVW and is another attempt to define an encoding with uniformity in the perceptibility ofcolor differences.^[4] The non-linear relations forL*,u*, andv* are given below:^[4]

The quantitiesu′_n andv′_n are the(u′,v′) chromaticity coordinates of a "specified white object" – which may be termed thewhite point – andY_n is its luminance. In reflection mode, this is often (but not always) taken as the(u′,v′) of theperfect reflecting diffuser under that illuminant. (For example, for the2° observer andstandard illuminant C,u′_n = 0.2009,v′_n = 0.4610.) Equations foru′ andv′ are given below:^[5][6]

The transformation from(u′,v′) to(x,y) is:^[6]

The transformation from CIELUV to XYZ is performed as follows:^[6]

CIELCh_uv, orHCL color space (hue–chroma–luminance) is increasingly seen in theinformation visualization community as a way to help with presenting data without the bias implicit in using varyingsaturation.^[7][8][9]

Thecylindrical version of CIELUV is known as CIELCh_uv, or CIELChuv, CIELCh(uv) or CIEHLC_uv, whereC*_uv is thechroma andh_uv is thehue:^[6]

${\displaystyle C_{uv}^{\ast }=\mathrm{hypot}(u^{\ast },v^{\ast })=\sqrt{(u^{\ast }{)}^2+(v^{\ast }{)}^2},}$

${\displaystyle h_{uv}=\mathrm{atan2}(v^{\ast },u^{\ast }),}$

whereatan2 function, a "two-argument arctangent", computes thepolar angle from a Cartesian coordinate pair.

Furthermore, the saturation correlate can be defined as

${\displaystyle s_{uv}=\frac{C^{\ast }}{L^{\ast }}=13\sqrt{(u^{\prime }-u_n^{\prime }{)}^2+(v^{\prime }-v_n^{\prime }{)}^2}.}$

Similar correlates of chroma and hue, but not saturation, exist for CIELAB. SeeColorfulness for more discussion on saturation.

Thecolor difference can be calculated using theEuclidean distance of the(L*,u*,v*) coordinates.^[6] It follows that a chromaticity distance of${\displaystyle \sqrt{(\mathrm{\Delta }{u}^{\prime }{)}^2+(\mathrm{\Delta }{v}^{\prime }{)}^2}=1/13}$ corresponds to the same ΔE*_uv as a lightness difference ofΔL* = 1, in direct analogy to CIEUVW.

The Euclidean metric can also be used in CIELCh, with that component of ΔE*_uv attributable to difference in hue as^[4]ΔH* =√C*₁C*₂ 2 sin (Δh/2), whereΔh =h₂ −h₁.

• YUV
• CIELAB color space

• Chromaticity diagrams, including the CIE 1931, CIE 1960, CIE 1976
• Colorlab MATLAB toolbox for color science computation and accurate color reproduction (by Jesus Malo and Maria Jose Luque, Universitat de Valencia). It includes CIE standard tristimulus colorimetry and transformations to a number of non-linear color appearance models (CIELAB, CIE CAM, etc.).

• Color space
• 1976 introductions

• Articles with short description
• Short description matches Wikidata