Do not use HSL normalized saturation and hue for certain spaces #582
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The current implementation of HSL normalizes negative saturation, and while the resultant values, if used as a base for HSV conversion, are compatible and will round trip well, it can often produce negative saturation in HSV for out of gamut colors in HSV just due to how the HSV algorithm is defined. Additionally, HWB currently uses HSV as a base for conversion and, if HSL negative saturation normalization is propagated through HSL -> HSV -> HWB, round trip can break down as the HWB algorithm does not mathematically account for such normalization. So HSV forces conversion directly through sRGB and will calculate an non-normalized HSL base for conversion. HSV can then be used safely as a base for HWB conversion.
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Before: > var { default: Color } = require("colorjs.io");
undefined
> new Color('lab', [100, 104.3, -50.9]).to('hwb').to('lab').coords
[ 81.53810579383484, 0, 0 ]
> new Color('lab', [100, 104.3, -50.9]).to('hsv').to('lab').coords
[ 100, 104.30000000000017, -50.90000000000008 ]
> new Color('lab', [100, 104.3, -50.9]).to('hsl').to('lab').coords
[ 100, 104.30000000000017, -50.90000000000008 ]After: > var { default: Color } = require("colorjs.io");
undefined
> new Color('lab', [100, 104.3, -50.9]).to('hwb').to('lab').coords
[ 100, 104.30000000000017, -50.90000000000008 ]
> new Color('lab', [100, 104.3, -50.9]).to('hsv').to('lab').coords
[ 100, 104.30000000000017, -50.90000000000008 ]
> new Color('lab', [100, 104.3, -50.9]).to('hsl').to('lab').coords
[ 100, 104.30000000000017, -50.90000000000008 ] |
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Nice, I just merged the PR on CSS Color 4 and was headed here to do the same change. |
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The current implementation of HSL normalizes negative saturation, and while the resultant values, if used as a base for HSV conversion, are compatible and will round trip well, it can often produce negative saturation in HSV for out of gamut colors in HSV just due to how the HSV algorithm is defined.
Additionally, HWB currently uses HSV as a base for conversion and, if HSL negative saturation normalization is propagated through HSL -> HSV -> HWB, round trip can break down as the HWB algorithm does not mathematically account for such normalization.
HSV is now calculated from sRGB directly which sidesteps the HSL hue/saturation normalization. In turn, HWB which uses HSV as the base for conversion will also not be affected by the HSL hue/saturation normalization.
w3c/csswg-drafts#10695