CIELUV

CIELUV, or the CIE 1976 Luv color space, is a three-dimensional color model defined by the International Commission on Illumination (CIE). It expresses colors by a lightness component, L, and two chromaticity coordinates, u and v, relative to a reference white point. CIELUV is derived from the CIE XYZ tristimulus values and is designed to provide a perceptually meaningful separation of lightness from chromaticity, with reference to a chosen illuminant such as D65.

To compute CIELUV values from XYZ and a reference white (Xn, Yn, Zn), first derive the chromaticity of the sample:

u' = 4X / (X + 15Y + 3Z)

v' = 9Y / (X + 15Y + 3Z)

Similarly, for the reference white:

u'n = 4Xn / (Xn + 15Yn + 3Zn)

v'n = 9Yn / (Xn + 15Yn + 3Zn)

Next determine lightness using Y relative to the white Yn:

If Y/Yn > 0.008856, L = 116(Y/Yn)^(1/3) - 16; otherwise L = 903.3(Y/Yn)

Finally, compute the chromaticity coordinates:

u = 13L(u' - u'n)

v = 13L(v' - v'n)

White points map to L ≈ 100 with u and v ≈ 0. The CIELUV space is related to CIELAB but uses a different reference framework for chromaticity; it is commonly used for color difference calculations (ΔEuv) and in color management where a separation of lightness and chromaticity is advantageous.

Applications of CIELUV include color difference evaluation, lighting and display technologies, and color specification. It is valued for its straightforward relationship to chromaticity and its alignment with perceptual judgments in certain lighting conditions, though some differences remain in perceptual uniformity compared with newer models like CIEDE2000.

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