Darker images captured when both option `hdr-reference-white = 100` and command `screenshot`

mpv Information

mpv v0.40.0-462-ge6885cb92 Copyright © 2000-2025 mpv/MPlayer/mplayer2 projects
built on Nov 19 2025 00:13:27
libplacebo version: v7.357.0 (v7.351.0-90-g2e5a392-dirty)
FFmpeg version: N-121806-gb39989604
FFmpeg library versions:
libavcodec      62.19.100
libavdevice     62.2.100
libavfilter     11.9.100
libavformat     62.6.103
libavutil       60.18.100
libswresample   6.2.100
libswscale      9.3.100
Configuration: -Ddebug=true -Db_ndebug=true -Doptimization=3 -Db_lto=true -Db_lto_mode=thin -Dlibmpv=true -Dpdf-build=enabled -Dlua=enabled -Djavascript=enabled -Dsdl2-gamepad=enabled -Dlibarchive=enabled -Dlibbluray=enabled -Ddvdnav=enabled -Duchardet=enabled -Drubberband=enabled -Dlcms2=enabled -Dopenal=enabled -Dspirv-cross=enabled -Dvulkan=enabled -Dvapoursynth=enabled -Dgl=enabled -Degl-angle=enabled -Dc_args=-Wno-error=int-conversion -Dprefix=/__w/mpv-winbuild-cmake/mpv-winbuild-cmake/build_x86_64_v3/x86_64_v3-w64-mingw32 -Dlibdir=/__w/mpv-winbuild-cmake/mpv-winbuild-cmake/build_x86_64_v3/x86_64_v3-w64-mingw32/lib -Ddefault_library=shared -Dprefer_static=True --cross-file=/__w/mpv-winbuild-cmake/mpv-winbuild-cmake/build_x86_64_v3/meson_cross.txt
[   0.001][v][cplayer] List of enabled features: build-date cplugins cuda-hwaccel cuda-interop d3d-hwaccel d3d11 d3d9-hwaccel debug direct3d dos-paths dvdnav dxgi-debug-d3d11 egl-angle egl-angle-win32 ffmpeg ffnvcodec gl gl-dxinterop gl-dxinterop-d3d9 gl-win32 glob glob-win32 gpl iconv javascript jpeg lcms2 libarchive libass libavdevice libbluray libplacebo luajit openal rubberband rubberband-3 sdl2-gamepad shaderc spirv-cross uchardet vaapi vaapi-win32 vapoursynth vector vulkan wasapi win32 win32-desktop win32-executable win32-smtc win32-threads zimg zimg-st428 zlib
Built with NDEBUG.
Command line options: '--config=no' '--log-file=mpv-pure.log' '--vo=gpu-next' '--idle=once' '--force-window=yes' '--keep-open=yes' '--hidpi-window-scale=no' '--autofit-smaller=500x500'

Other Information

- Windows version: win11
- GPU model, driver and version: irrelevant
- Source of mpv: shin
- Latest known working version: n/a
- Issue started after the following happened: n/a

Reproduction Steps

start mpv with --hdr-reference-white=100

run the command screenshot

Expected Behavior

Just a common screenshot

Actual Behavior

a darker screenshot

Log File

test.log

Sample Files

No response

I carefully read all instruction and confirm that I did the following:

• I tested with the latest mpv version to validate that the issue is not already fixed.
• I provided all required information including system and mpv version.
• I produced the log file with the exact same set of files, parameters, and conditions used in "Reproduction Steps", with the addition of --log-file=output.txt.
• I produced the log file while the behaviors described in "Actual Behavior" were actively observed.
• I attached the full, untruncated log file.
• I attached the backtrace in the case of a crash.

No source files or tests are named. Start by reproducing the issue with --hdr-reference-white=100 and the screenshot command, then use the attached log while tracing the screenshot and HDR rendering paths. Done means screenshots no longer appear darker under these conditions, with a regression test if the project’s existing test setup supports it.