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staging/color-management: redefine set_luminance

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The BT.1886 recommendation is impossible to implement precisely if
min_lum includes other sources than the display emission. BT.1886
transfer function requires L_W and L_B to determine the function
parameters black level lift and gain. The black level lift changes the
non-linearity, and cannot be implemented as an optical addition.

I believe the inclusion of optical additives, particularly the ambient
flare, came from sRGB specification. I do not recall seeing it anywhere
else.

Drop the optical additives from the definitions of the luminances. It
was probably incorrect for everything but sRGB, if they even had it
specified at all. This allows implementing BT.1886 as specified.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
This commit is contained in:
Pekka Paalanen 2025-06-05 11:44:42 +03:00 • committed by Pekka Paalanen
parent fff667c829
commit 8271c366e4
1 changed files with 2 additions and 2 deletions
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4
staging/color-management/color-management-v1.xml
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@ -1132,8 +1132,8 @@
<request name="set_luminances">
<description summary="primary color volume luminance range and reference white">
Sets the primary color volume luminance range and the reference white
luminance level. These values include the minimum display emission
and ambient flare luminances, assumed to be optically additive and have
luminance level. These values include the minimum display emission, but
not external flare. The minimum display emission is assumed to have
the chromaticity of the primary color volume white point.
The default luminances from