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Does anyone know why HUSL is based on CIELUV rather than CIELAB? It seems that, although CIELUV and CIELAB were considered equally good when adopted in 1976, C

• jacobolus 11y ago
  The CIE 1976 (u', v') UCS chromaticity diagram is a somewhat better chromaticity diagram than the standard 1931 (x, y) version for e.g. showing chromaticity of the primaries on a computer display: it reduces some of the dramatic perceptual distortions of xy. CIELUV is supposed to be a full 3D color space made out of a combination of a (very bad) chromatic adaptation method, the same lightness L* from CIELAB, and color coordinates L* u* v* which are simply derived from L*, u', and v'. In theory, CIELUV is a bit more directly relevant to colored lights or images on a television / computer display, whereas CIELAB is defined for surface colors. In practice, CIELUV just isn’t a very good uniform model of human color vision, and CIELAB is somewhat better (even for display colors) while still being quite easy to compute. The reason color difference measures are defined with reference to CIELAB coordinates is that they are typically used for specifying tolerances on surface colors in industry. For instance, you might specify that a particular textile or paint color must be within a particular perceptual distance of a target color. CIELUV wouldn’t make any sense for such a use case. Personally, I’d recommend people move on to use IPT or CIECAM02 or something similar instead.