Deband grain is far too strong

mpv Information

mpv v0.41.0-918-g1d1568614 Copyright © 2000-2026 mpv/MPlayer/mplayer2 projects
 built on Aug  2 2026 12:32:00
libplacebo version: v7.371.0 (v7.360.0-109-g4d82c68-dirty)
FFmpeg version: N-125907-ga7e72069f
FFmpeg library versions:
   libavcodec      63.7.100
   libavdevice     63.2.100
   libavfilter     12.3.101
   libavformat     63.5.101
   libavutil       61.5.100
   libswresample   7.2.100
   libswscale      10.2.100

Other Information

- Windows version: 11
- GPU model, driver and version: RTX 4080, Game Ready 610.88
- Source of mpv: https://github.com/zhongfly/mpv-winbuild/releases
- Latest known working version: mpv-x86_64-20260610-git-304426c
- Issue started after the following happened: After updating mpv to latest, but it happens as far back as mpv-x86_64-20260704-git-33111f3212 (probably earlier, this is the oldest zhongfly offers)
It doesn't occur with vo=gpu or gpu-api=opengl
It doesn't show up in mpv screenshots, so I also took some with ShareX
https://slow.pics/c/VNywxdPd

Reproduction Steps

Enable deband

Expected Behavior

Debands the video with a small amount of grain

Actual Behavior

Debands the video with a huge amount of grain

Log File

output.txt

Sample Files

No response

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 by reproducing the issue with deband enabled using the conditions in output.txt, then compare the affected GPU path with vo=gpu and gpu-api=opengl, where it does not occur. Inspect the deband rendering path and use screenshots to verify the result: the GPU output should retain debanding while producing only a small amount of grain.