Re: [csswg-drafts] [css-color-4] Define gamut mapping (#5191)

Hi @LeaVerou 

> _LCH chroma reduction is a common one, but fails terribly for yellows, producing results far worse than even simple component clipping._

I've been conducting some experiments here to remap only based on the CSS color, knowing little or nothing about the surrounds. In some ways it is similar to the contrast problem, though multiplied — and since gamut mapping affects contrast.... YIKES!!

I've been experimenting with various appearance models including SAPC variants and other experimental code. I don't have concrete answers yet.

**One thing:** in film and TV we (almost by default) use weighted soft-clipping, especially for one-light dailies and some temp proxies. Of course final grading is done manually, shot by shot, by a colorist with a system like DaVinci Resolve (which you can download free).

And also everything we do uses LUTs — lots and lots of LUTs. But ultimately, the color grade is a time consuming manual operation.

There is no "really wonderful" gamut mapping magical bullet, well, except my friend Stu's invention that happens to be called Magic Bullet, LOL. And it is basically a fancy adjustable LUT.

### What's my point already...?

## LUTS! 

There are a small, finite number of spaces. And it is even easier for web content because everything is on a self illuminated display, everything is an RGB color model, and everything is the standard D65.
_(except ProPhoto & I still don't understand why a non-display profile like ProPhoto is in CSS, and ICC v2/v4 PCS which has limited utility for web content and is a performance hog, totally useless for streaming)._

LUTs are already in use to some degree on the user-side for device profiles. A LUT for working-space to a display space is typically considered the best practice outside of manual color grading. An RGB -> RGB LUT is typically small and efficient, unlike an RGB -> CMYK LUT. This also gives some control back to the author: a set of LUTs sent as a single file, perhaps in the CSS. Fingerprinting is less a concern as all the LUTs will be there and a media query will select the appropriate one.

### AccessibLUT

Another advantage is the potential creation of "accessible fallback LUTs" that could in one file increase/decrease contrast, saturation, polarity (maintaining correct contrast) etc etc.

Andy

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Received on Monday, 1 March 2021 10:10:48 UTC