https://bugs.kde.org/show_bug.cgi?id=513895
Bug ID: 513895
Summary: HDR content looks different in window mode and
fullscreen. Direct scanout lacks luminance clipping.
Classification: Plasma
Product: kwin
Version First 6.5.4
Reported In:
Platform: Arch Linux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: colour-management
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
SUMMARY
HDR content has a mastering luminance, f.e. 1000, 2000, 5000 or 10.000 nits.
The display has a maximum brightness it can display, f.e. 1150 nits. Plasma
allows to limit the display to a number below its capabilities in the system
settings to a value <= the display's capability, f.e. to 1000 nits.
For HDR content that has a higher mastering luminance than the set limit in the
system settings, KWin has to do some sort of luminance limiting to prevent an
image that is too bright and shows color artifacts. This works when an
application is in windowed mode or in fullscreen, but the hardware cursor is
still shown. Unfortunately this color transformation seems not to be active,
when applications get into the state "direct scanout", which can happen when
they are in fullscreen and the cursor goes away.
This can be seen using mpv with the parameters and a video that has a mastering
luminance higher than the set limit in the system settings: `mpv
--vo=dmabuf-wayland "path/to/video"`
To show the issue drastically one can use a 10.000 nits video file.
This leads to the problem that full screen video with a mastering luminance
higher than the set limit in kwin cannot be accurately displayed, sometimes
making the image unwatchable.
As far as I can understand, kwin should be able to apply luminance limiting
also in direct scanout, so fullscreen applications can display HDR content the
same as non fullscreen applications.
STEPS TO REPRODUCE
1. Activate HDR in KDE Plasma with a monitor that has less than 10.000 nits of
max. luminance.
2. Open a video file with a mastering luminance of 10.000 nits in mpv with `mpv
--vo=dmabuf-wayland "path/to/video"`, enable fullscreen and wait three seconds
until the mouse cursor disappears.
OBSERVED RESULT
As soon as the mouse cursor disappears (and direct scanout gets activated) the
image becomes a lot brighter and obviously incorrect.
EXPECTED RESULT
As soon as the mouse cursor disappears the image should stay the same as with
mouse cursor or as in windowed mode.
SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 6.5.4
KDE Frameworks Version: 6.21.0
Qt Version: 6.10.1
Kernel Version: 6.18.2-arch2-1 (64-bit)
Graphics Platform: Wayland
Processors: 24 × AMD Ryzen 9 5900X 12-Core Processor
Memory: 32 GiB of RAM (31.3 GiB usable)
Graphics Processor: AMD Radeon RX 6900 XT
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