From 8271c366e4c34421a18e6f32cfd928f5ceb68be3 Mon Sep 17 00:00:00 2001 From: Pekka Paalanen Date: Thu, 5 Jun 2025 11:44:42 +0300 Subject: [PATCH] staging/color-management: redefine set_luminance 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 --- staging/color-management/color-management-v1.xml | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/staging/color-management/color-management-v1.xml b/staging/color-management/color-management-v1.xml index 16a39ca..dda6b94 100644 --- a/staging/color-management/color-management-v1.xml +++ b/staging/color-management/color-management-v1.xml @@ -1132,8 +1132,8 @@ 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