Re: [csswg-drafts] [css-color-4] Premultiplication in cylindrical spaces and mixing (#11238)

I'm still needing to be convinced, both the example and the argument from math.

The huge discrepancy in the second example is caused by hue fixup. That is most definitely a complication (and I hadn't thought about that in my initial analysis), but I don't think it's a showstopper. Hue fixup can be defined in terms of un-premultiplying, and then in turn can be evaluated efficiently without division with some algebraic manipulation (basically it's `h1 * a2 - h2 * a1 > 180 * a1 * a2` being equivalent to `h1 / a1 - h2 / a2 > 180`).

And I don't quite follow the argument about affine spaces, and don't think compositing is restricted to coordinates that have a meaningful concept of scaling. Ultimately, the final output is a weighted sum of values, and if the weights sum to 1 then I don't see a fundamental mathematical problem.

Of course, the hue fixup *is* a real source of trouble, and the fact it can create discontinuities is a good reason to not consider it form of compositing. But there are ways to get discontinuities from blend modes also.


-- 
GitHub Notification of comment by raphlinus
Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/11238#issuecomment-2486839801 using your GitHub account


-- 
Sent via github-notify-ml as configured in https://github.com/w3c/github-notify-ml-config

Received on Tuesday, 19 November 2024 22:00:17 UTC