https://bugs.kde.org/show_bug.cgi?id=527279
Bug ID: 527279
Summary: Color discrepancy between composited vs drm color
pipeline (direct scanout)
Classification: Plasma
Product: kwin
Version First 6.8.0
Reported In:
Platform: Arch Linux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
DESCRIPTION
My GPU is AMD Radeon 680M. When Firefox or mpv is full-screen, there is a
subtle but noticeable color change when bringing other window on top, e.g. by
opening krunner or alt-tab an window.
The full-screen Firefox or mpv is under direct scanout, confirmed by the lack
of red outline from "show compositing" kwin effect. DRM color pipeline usage
can be seen in drm_info. If "Color accuracy" is set to "Prefer color accuracy"
then the color discrepancy does not appear.
For Firefox (158.0), I tested with this very page
(https://bugs.kde.org/enter_bug.cgi?product=kwin), the gray on the side seems a
bit darker under direct scanout than composited. In https://lwn.net/Kernel/,
the gray horizontal strips are darker under direct scanout. In the built-in
about:support page, the purple is also darker.
For mpv (v0.41.0-1200-gdde067107), the command is "mpv --no-config
--hwdec=vulkan,vaapi --vo=gpu-next --target-colorspace-hint-mode=source
<video>" (target-colorspace-hint-mode=source because this way mpv presents an
RGB format buffer instead of YUV for direct scanout, while still letting kwin
do the color conversion from video to monitor).
I tested with an SDR/Rec.709 video
(https://www.youtube.com/watch?v=YThelfB2fvg) and an HDR/PQ video (Camp by
Sony). Both video changes color tint slightly when krunner pops up, especially
for red or orange.
STEPS TO REPRODUCE
1. Open Kwin debug console and enable "showcompositong"
2. Make Firefox or mpv full-screen and confirm it is in direct scanout (the
lack of red outline)
3. Press alt+space to bring up krunner to exit direct scanout. Notice color
changes.
OBSERVED RESULT
The color changes slightly when krunner appear.
EXPECTED RESULT
The color should stay the same.
SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 6.8.0
KDE Frameworks Version: 6.31.0
Qt Version: 6.12.0
Kernel Version: 7.2.9-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 PRO 6850HS with Radeon Graphics
Memory: 16 GiB of RAM (14.9 GiB usable)
Graphics Processor: AMD Radeon Graphics
ADDITIONAL INFORMATION
I am using an HP laptop (Elitebook 849 G9), connected to external monitor with
a USBC-DP cable. Both monitors have the same color change behavior:
- Redmi G27U 2026 from Xiaomi. I use it in SDR standard mode (wide gamut
similar to P3). In KDE settings, color profile is set to built-in (from EDID),
color accuracy is prefer efficiency.
- Laptop monitor. EDR is disabled. Color profile is None, color accuracy is
also prefer efficiency.
Though full-screen color change is probably not very distracting, it surely is
when combined with overlay plane support: with KWIN_USE_OVERLAYS=1, many
programs will change color frequently and irregularly, depending on whether it
is suitable for overlay plane.
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