https://bugs.kde.org/show_bug.cgi?id=511493
Bug ID: 511493
Summary: [Plasma 6.5.1] HDR content is severely overexposed and
DDC/CI brightness control fails after enabling HDR
mode
Classification: Plasma
Product: plasmashell
Version First 6.5.1
Reported In:
Platform: Arch Linux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: 1.0
Created attachment 186402
--> https://bugs.kde.org/attachment.cgi?id=186402&action=edit
HDR
SUMMARY [Plasma 6.5.1] HDR content is severely overexposed and DDC/CI
brightness control fails after enabling HDR mode
STEPS TO REPRODUCE
Start with the system in standard SDR mode. Confirm that DDC/CI brightness
control is fully functional via Plasma's brightness slider or keyboard
shortcuts.
Enable HDR mode in System Settings > Display & Monitor.
Play any native HDR content (e.g., an HDR video file or an HDR-enabled game).
Attempt to adjust the screen brightness using the Plasma brightness slider.
OBSERVED RESULT
Overexposure of HDR Content: Native HDR content is displayed with severe
overexposure. Bright areas of the image ("highlights") are completely blown
out, leading to a significant loss of detail and a "clipped" appearance.
Brightness Control Failure: Immediately after HDR is enabled, all brightness
control ceases to function. DDC/CI, which was working perfectly in SDR mode,
becomes completely unresponsive. The brightness slider can be moved, but it has
no effect on the actual screen luminance.
Diagnostic tools confirm the issue: running kscreen-doctor -o shows that
brightness control is stuck at 100% (Brightness control: supported, set to 100%
and dimming to 100%).
EXPECTED RESULT
HDR content should be correctly tone-mapped without overexposing highlights.
The system's brightness control should remain functional after enabling HDR,
allowing the user to adjust the overall screen brightness to a comfortable
level (likely via a software dimming mechanism, since DDC/CI is often disabled
by the monitor in HDR mode).
SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 6.5.1
KDE Frameworks Version: 6.19.0
Qt Version: 6.10.0
Kernel Version: 6.12.56-1-lts (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 5600X 6-Core Processor
Memory: 32 GiB of RAM (31.3 GiB usable)
Graphics Processor: AMD Radeon RX 7900 XTX
ADDITIONAL INFORMATION This appears to be a critical regression in Plasma
6.5.1, where enabling HDR mode simultaneously breaks brightness control and
causes incorrect tone mapping.
The key observation is the direct link between the two issues: DDC/CI
brightness control works flawlessly in SDR mode but fails the instant HDR is
activated.
My hypothesis is that a failure in KWin's brightness control mechanism for HDR
mode is causing the monitor's backlight to remain at its maximum physical
level. However, KWin's compositor seems to be rendering the HDR content based
on the configured SDR reference brightness (200 nits in my case), assuming a
much dimmer baseline. This severe mismatch between the software rendering
intent and the actual hardware brightness level results in the final image
being drastically overexposed.
This issue is separate from the UI blur saturation changes tracked in bug
#510818.
Diagnostic Information (kscreen-doctor -o output):
Output: 1 DP-3 a57eaaef-a13d-451c-867f-54f3db0e791a
enabled
connected
priority 1
DisplayPort
replication source:0
Modes: 1:[email protected]*! 2:[email protected] 3:[email protected]
4:[email protected] 5:[email protected] 6:3
[email protected] 7:[email protected] 8:[email protected] 9:[email protected]
10:[email protected] 11:[email protected] 12:256
[email protected] 13:[email protected] 14:[email protected] 15:[email protected]
16:[email protected] 17:[email protected] 18
:[email protected] 19:[email protected] 20:[email protected] 21:[email protected]
22:[email protected] 23:[email protected]
24:[email protected] 25:[email protected] 26:[email protected] 27:[email protected]
28:[email protected] 29:[email protected] 30
:[email protected] 31:[email protected] 32:[email protected] 33:[email protected]
34:[email protected] 35:[email protected] 36:720x576
@50.00 37:[email protected] 38:[email protected] 39:[email protected] 40:[email protected]
41:[email protected] 42:[email protected] 43:7
[email protected] 44:[email protected] 45:[email protected] 46:[email protected]
47:[email protected] 48:[email protected] 49:1
[email protected] 50:[email protected] 51:[email protected] 52:[email protected]
53:[email protected] 54:[email protected] 55:
[email protected] 56:[email protected] 57:[email protected] 58:[email protected]
59:[email protected] 60:[email protected] 61:
[email protected]
Geometry: 0,0 1920x1080
Scale: 2
Rotation: 1
Overscan: 0
Vrr: Automatic
RgbRange: unknown
HDR: enabled
SDR brightness: 200 nits
SDR gamut wideness: 0%
Peak brightness: 1350 nits, overridden with: 1350 nits
Max average brightness: 911 nits
Min brightness: 0 nits
Wide Color Gamut: enabled
ICC profile: none
Color profile source: EDID
Color power preference: prefer efficiency and performance
Brightness control: supported, set to 100% and dimming to 100%
DDC/CI: allowed
Color resolution: automatic (10), range: [8; 16] bits per color
Allow EDR: unsupported
Sharpness control: unsupported
--
You are receiving this mail because:
You are watching all bug changes.
