Clamping out-of-gamut lab/lch colors
carlosame opened this issue · comments
The current procedure to clamp out-of-gamut colors when converting from lab() and lch() to RGB (sRGB color space) in toRGBColorValue() and CSSColorValue.toRGBColorValue(boolean) is inadequate, and a more elaborated process should be used.
This issue is opened as a reminder that whatever comes out from CSSWG's (csswg-drafts) issue 5191 should be looked upon.
I want to ship Lab/LCh with version 3.4.0, so I implemented a procedure close to the spirit of what is being discussed in CSSWG's issue 5191: perform a chromaticity reduction until the clipped value is within a ΔE2000 of 2 from the non-clipped RGB.
Here are some figures from the unit tests, where ΔE2000 is the distance from the original to the clamped color:
| Original | RGB | ΔE2000 |
|---|---|---|
| lab(54.2324% 80.9288 70.8493) | #f00 | 0.334 |
| lab(72% 15.9649 130.0235) | rgb(85.74%, 65.89%, 0%) | 9.948 |
| lab(59% -100.8654 78.8047) | rgb(0%, 65.42%, 16.8%) | 9.727 |
| lch(54.2324% 107.5597 41.2006) | #f00 | 0.334 |
| lch(72% 131 83) | rgb(85.74%, 65.89%, 0%) | 9.948 |
| lch(59% 128 142) | rgb(0%, 65.42%, 16.8%) | 9.727 |
Closing the issue.