[css-color-hdr] Should CSS filters produce HDR results?

[smfr]

Should filter: brightness(2) result in HDR output on a capable display?

[smfr]

cc @ccameron-chromium

[ccameron-chromium]

Scattered thoughts:

My inclination is that this shouldn't make things that weren't HDR become HDR. It should clamp colors to wherever they were clamped before.

But what happens if this is applied to already-HDR content, or a mix of HDR content?

This API is not a good one for enabling HDR, because it works in absolute headroom (and we don't want to expose that, either for privacy or for performance reasons).

[svgeesus]

CSS filters are, as currently specified and implemented, restricted to sRGB and clamped to the [0, 1] range. Even extending them to SDR P3 is problematic