[kwin] [Bug 524038] New: HDR ICC profile in KWin 6.7.4 crushes PQ blacks and compresses midtones

https://bugs.kde.org/show_bug.cgi?id=524038

            Bug ID: 524038
           Summary: HDR ICC profile in KWin 6.7.4 crushes PQ blacks and
                    compresses midtones
    Classification: Plasma
           Product: kwin
      Version First 6.7.4
       Reported In:
          Platform: Other
                OS: Linux
            Status: REPORTED
          Severity: major
          Priority: NOR
         Component: colour-management
          Assignee: [email protected]
          Reporter: [email protected]
                CC: [email protected]
  Target Milestone: ---

SUMMARY

Applying an HDR ICC profile in KWin 6.7.4 severely crushes the lower PQ curve
and compresses midtones. The same profile produces the expected PQ response
when its BToA cLUT is applied in the native Wayland HDR test application
instead of by KWin.

This profile was created while the display was in HDR mode. The profiling
patches were submitted by a native Wayland client using a Vulkan HDR10 ST 2084
swapchain. DisplayCAL and XWayland were not used.

STEPS TO REPRODUCE

1. Enable HDR on the display.
2. Assign the attached ICC profile as the HDR ICC profile in Display
Configuration.
3. Select the ICC profile as the HDR color profile source.
4. Display neutral HDR10 ST 2084 patches through a native Wayland client.
5. Measure 20%, 30%, 50%, and 100% PQ patches.
6. Change the HDR color profile source back to EDID.
7. Apply the same profile's BToA cLUT inside the native Wayland test client.
8. Repeat the same patches without changing the display, meter, signal format,
or patch geometry.

OBSERVED RESULT

With KWin applying the profile:

    PQ input    Measured luminance
    20%         No meter reading
    30%         0.758 cd/m2
    50%         51.425 cd/m2
    100%        307.868 cd/m2

With the same profile applied locally by the native HDR client:

    PQ input    ST 2084 value    Measured luminance
    20%         2.429 cd/m2       2.416 cd/m2
    30%         10.038 cd/m2      10.033 cd/m2
    50%         92.246 cd/m2      92.543 cd/m2
    100%        Display clips     307.726 cd/m2

With KWin applying the profile, 5%, 10%, and 15% all measured as black. The
profile's local cLUT result follows ST 2084 closely from 20% through 50% and
reaches the same display peak.

The attached profile has a 33 point AToB0 cLUT, a 33 point BToA0 cLUT, 2048
entry input and output tables, 256 entry TRCs, matrix tags, and no MHC2 or VCGT
tag. Its SHA-256 is:

    2b704808224e5109baea26551cd16b2c41a7b972db95ae1af490c2f259644281

EXPECTED RESULT

KWin should apply the profile without changing the intended PQ luminance
response. The result should be comparable to applying the same BToA cLUT in the
native HDR client.

ADDITIONAL TESTS

An MHC2 version of the profile produced nearly the same result through KWin:

    PQ input    Measured luminance
    20%         No meter reading
    30%         0.763 cd/m2
    50%         50.930 cd/m2
    100%        308.534 cd/m2

Changing the ICC lumi tag to 1000 cd/m2 did not correct the curve. Changing the
Wayland surface reference luminance, mastering luminance metadata, and render
intent also did not correct it. The local cLUT and KWin tests used the same
display, 10% patch size, HDMI full range output, meter, and patch values.

The display profile was built from 424 valid measured characterization patches
and a separate 254 point neutral measurement. ArgyllCMS generated the ICC
profile. Internal profile validation reported average Delta E 2000 of 0.459 and
95th percentile of 1.644.

SYSTEM INFORMATION

Operating System: Fedora Linux 44 KDE Plasma Desktop Edition
KDE Plasma Version: 6.7.4
KWin Version: 6.7.4
KDE Frameworks Version: 6.28.0
Qt Version: 6.11.1
Kernel Version: 7.1.6-201.fc44.x86_64
Mesa Version: 26.1.5
Graphics Platform: Wayland
GPU: AMD Phoenix1, amdgpu
Display: YCT Innoview AMOLED connected over HDMI
HDR: enabled
Output range: full
VRR: disabled
Patch client: PGenerator+ Patch Companion 1.4.7, Vulkan renderer, native
Wayland HDR10 ST 2084 surface
Meter: Calibrite/X-Rite i1Display Pro Plus
Patch geometry: borderless fullscreen with a centered 10% window

ATTACHMENTS

1. Innoview_Fedora_Dense_256_Neutral_KDE-KDE-HDR-XYZ-cLUT-matrix.icc
2. dense256-local-clut-validation.json
3. dense256-kwin-system-validation.json
4. Innoview_Fedora_Dense_MHC2-HDR-MHC2-XYZ-cLUT-matrix.icc
5. kwin-mhc2-system-validation.json

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