hdr tonemapping: target-peak + hdr-compute-peak=yes desaturates and breaks the image in dark scenes (saturation, contrast, brightness)

mpv Information

mpv v0.39.0-355-g45c1c586 Copyright © 2000-2024 mpv/MPlayer/mplayer2 projects
 built on Nov 19 2024 00:07:00
libplacebo version: v7.349.0 (v7.349.0-26-g5788a82-dirty)
FFmpeg version: N-117832-ge9c3698ed
FFmpeg library versions:
   libavcodec      61.25.100
   libavdevice     61.4.100
   libavfilter     10.6.101
   libavformat     61.9.100
   libavutil       59.47.100
   libswresample   5.4.100
   libswscale      8.9.101

Other Information

Windows version: Windows 10 22H2 Build 19045.4170)
GPU model, driver and version: intel HD Graphics 4600, driver: 20.19.15.5171
Source of mpv: https://sourceforge.net/projects/mpv-player-windows/files/
Introduced in version: present since v38.0

Reproduction Steps

With target-trc=bt.1886 and target-prim=bt.709
when you set target-contrast=1000 and target-peak=auto the image gets almost black and white in a dark scene. When you change target-peak to 10 then you get the colors back.

target-prim=bt.709
target-trc=bt.1886
tone-mapping=st2094-10
hdr-compute-peak=no
allow-delayed-peak-detect=yes

Expected Behavior

saturation stays the same

Actual Behavior

dark scenes get desaturated and look washed out

Log File

full output
output full.txt
gpu-debug
output.txt

Sample Files

almost black and white

normal

washed out

normal

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.

Start by reproducing the dark-scene comparison using the listed target-prim, target-trc, tone-mapping, target-contrast, target-peak, and hdr-compute-peak settings. Review full.txt and output.txt alongside the reproduction, then confirm the fix preserves saturation, contrast, and brightness when target-peak is auto rather than a fixed value.