Re: [csswg-drafts] [css-color-6] add color functions for some (or all) compositing/blending operations (#8431)

So, in terms of specifying this: we should presumably reference [General Formula for Compositing and Blending](https://drafts.fxtf.org/compositing-1/#generalformula) from Compositing 1. However, that spec is silent about colorspace, at least in the normative parts, and simply refers to "the premultiplied color". 

The examples use Red Green and Blue, natural given the age of the spec, and at the time sRGB would be assumed. The more complex parts such as blend modes even use the NTSC luma formula (operating on gamma-encoded RGB values)

> Lum(C) = 0.3 x Cred + 0.59 x Cgreen + 0.11 x Cblue

but that doesn't affect the simple `color-over(<color>#)` being proposed here. Assuming sRGB though, implies either

1. Forcing all colors to be in the sRGB gamut, which is undesirable, or
2. Converting all colors to extended-range sRGB and verifying that the formulae do something sensible with negative component values, or component values greater than 1

I recall hearing that on some systems, compositing happens in the native RGB colorspace of the display (eg P3).

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Received on Monday, 29 July 2024 12:33:26 UTC