--image-subs-hdr-peak doesn't work on hdr display

mpv Information

mpv v0.41.0-687-gdb7385799 Copyright © 2000-2026 mpv/MPlayer/mplayer2 projects
 built on May 22 2026 00:26:43
libplacebo version: v7.364.0 (v7.360.0-55-g464d6ea-dirty)
FFmpeg version: N-124570-gb67570b76
FFmpeg library versions:
   libavcodec      62.34.100
   libavdevice     62.4.100
   libavfilter     11.17.100
   libavformat     62.18.100
   libavutil       60.31.100
   libswresample   6.4.100
   libswscale      9.7.100

and

mpv v0.41.0 Copyright © 2000-2025 mpv/MPlayer/mplayer2 projects
 built on Dec 25 2025 15:27:46
libplacebo version: v7.358.0 (v7.351.0-106-gbc90ef9-dirty)
FFmpeg version: N-122267-gabb152413
FFmpeg library versions:
   libavcodec      62.23.102
   libavdevice     62.2.100
   libavfilter     11.10.101
   libavformat     62.8.101
   libavutil       60.20.100
   libswresample   6.2.100
   libswscale      9.3.100

Other Information

- Windows version: Microsoft Windows [Version 10.0.26200.8457]
- GPU model, driver and version: nvidia rtx3090, 596.36
- Source of mpv: scoop
- Latest known working version: I don't know any
- Issue started after the following happened:

Reproduction Steps

mpv --no-config --gpu-debug --vo=gpu-next --log-file=mpv.log --image-subs-hdr-peak=10 --blend-subtitles <file>

Expected Behavior

subtitles should be dimmer.

Actual Behavior

subtitles still shows in bright white, seemingly no change from not setting it.

I tried with and without --blend-subtitles, no difference.

I've tried on the 0.41 stable and latest mpv-git on scoop, same behavior.

Log File

mpv.log

Sample Files

I've tested multiple hdr files with pgs subtitles, they behave the same, so I guess there's no need to upload a particular file, correct me if I'm wrong.

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

• I tested and confirmed that the issue exists with the latest release version or newer.
• 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.

Start with the reproduction command and attached mpv.log, focusing on --image-subs-hdr-peak, --blend-subtitles, and the gpu-next video-output path. Compare runs with and without --image-subs-hdr-peak on the reported HDR display; done means subtitle brightness changes as expected while the existing reproduction conditions remain valid.