From dceda690c040c9842bab4a14385e40bd94bb7ebe Mon Sep 17 00:00:00 2001 From: Pekka Paalanen Date: Tue, 10 Jun 2025 14:58:26 +0300 Subject: [PATCH] staging/color-management: recommend gamma22 instead of srgb https://gitlab.freedesktop.org/pq/color-and-hdr/-/blob/main/doc/wayland_qa.md#q-should-srgb-content-be-decoded-with-the-piecewise-srgb-transfer-function I found it unfortunate that we left in a TF code that will intuitively be used incorrectly. It is as if we designed the protocol so that compositors will need to fix up client image descriptions. I am not aware of any use case that would want to target a display with the sRGB piece-wise transfer function, that would be a non-standard display. This patch does not help compositors avoid needing to second-guess client image descriptions using srgb TF, but it at least documents the situation. We could choose to out-law srgb TF in a minor version bump, or drop it completely in the next major version. Compositors can also not advertise support for srgb TF. Signed-off-by: Pekka Paalanen --- staging/color-management/color-management-v1.xml | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/staging/color-management/color-management-v1.xml b/staging/color-management/color-management-v1.xml index ee482c5..4c1bc75 100644 --- a/staging/color-management/color-management-v1.xml +++ b/staging/color-management/color-management-v1.xml @@ -290,6 +290,8 @@ of Federal Regulations 73.682 (a) (20) - Rec. ITU-R BT.1700-0 625 PAL and 625 SECAM Equivalent to H.273 TransferCharacteristics code point 4. + + Note: an sRGB display (IEC 61966-2-1) uses this transfer function. @@ -340,6 +342,10 @@ - IEC 61966-2-1 sRGB Equivalent to H.273 TransferCharacteristics code point 13 with MatrixCoefficients set to 0. + + Note: This is not appropriate for describing sRGB material. + sRGB material is intended to be viewed on an sRGB display, and + that is described by gamma22.