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Incorret HCL interpolation between saturated colors and black #310

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aarthificial opened this issue Feb 26, 2023 · 2 comments
Open

Incorret HCL interpolation between saturated colors and black #310

aarthificial opened this issue Feb 26, 2023 · 2 comments

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@aarthificial
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aarthificial commented Feb 26, 2023

Description
When using the hcl/lch color space for interpolating between saturated colors and black, the resulting value is not correct:

interpolate('#f00', '#000', 1, 'hcl').hex() // #5b0000 (should be #000000)

The problem occurs only if one of the colors is pure black. Increasing the brightness even sliglty results in a correct color:

interpolate('#f00', '#010101', 1, 'hcl').hex() // #010101

Similarly, if the other color has no saturation, the interpolation is also correct:

interpolate('#ccc', '#000', 1, 'hcl').hex() // #000000

Possible explanation
It seems that this may be caused by the interpolator used for hcl/lch:

} else if (!isNaN(hue0)) {
hue = hue0;
if ((lbv1 == 1 || lbv1 == 0) && m != 'hsv') sat = sat0;
} else if (!isNaN(hue1)) {
hue = hue1;
if ((lbv0 == 1 || lbv0 == 0) && m != 'hsv') sat = sat1;

If one of the colors has a NaN hue and lb == 0 (pure black), the saturation is taken as-is from the other color.
This means that interpolate('#f00', '#000', 1, 'hcl') results in hcl(40, 104, 0) instead of hcl(40, 0, 0).

Version
2.4.2

@bkahlert
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bkahlert commented May 1, 2023

@aarthificial Did you try oklch? According to https://evilmartians.com/chronicles/oklch-in-css-why-quit-rgb-hsl#oklch-vs-hsl it's better than HCL it performs better in blue colors but maybe it coincidently it of help.

@aarthificial
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@bkahlert Thanks for the suggestion!
We use chroma.js to handle colors in Motion Canvas and this problem was reported by one of our users.
I told them to use a different color space but it would be great to have it fixed here.

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