Instead of just clipping when HDR content is brighter than the maximum luminance the
screen can show, when HDR metadata indicates this could happen, KWin now
- converts the rgb colors to ICtCp, to split luminance and color
- applies a tone mapping curve that maps the intensity component from
- [0, reference] to [0, newReference] linearly
- [reference, max content luminance] to [newReference, max display luminance] nonlinearly
- converts the resulting ICtCp color back to rgb
The result is that HDR content looks much, much better on SDR displays, at least when decent
HDR metadata is provided.
As wrong metadata could cause this tone mapping to wrongly kick in in games for example, the
environment variable KWIN_DISABLE_TONEMAPPING is provided to disable tone mapping and fall back
to clipping again instead.
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