[FFmpeg-user] Problems controlling sws-scale dithering.

[Steinar Apalnes]

fre. 25. jun. 2021 kl. 10:14 skrev Steinar Apalnes <steipal at gmail.com>:

> Hi,
>
> I'm having difficulty controlling dithering when video bit depth goes
> down. The following command illustrates the problem:
>
> ffplay.exe -f lavfi -i mandelbrot -sws_dither none -vf
> scale=sws_dither=none,format=rgb8
>
> I'm just using ffplay to visually show the undesired effect. Normal
> operation would be with ffmpeg but the outcome is the same in both cases.
> The image goes down from 8 bit to 3 bit per component and is dithered, even
> though I'm trying to turn it off dithering. So I'm interested in
> controlling dithering in the sws-scaler in general but cannot find the
> means to do it. Either it's not working properly or I'm doing something
> wrong.
>
> -steinar
>

Sorry, forgot:

ffplay version N-102783-gc010994fa7 Copyright (c) 2003-2021 the FFmpeg
developers
  built with gcc 10.3.0 (Rev2, Built by MSYS2 project)
  configuration:  --disable-static --enable-shared --pkg-config=pkgconf
--cc='ccache gcc' --cxx='ccache g++' --disable-autodetect --enable-amf
--enable-bzlib --enable-cuda --enable-cuvid --enable-d3d11va --enable-dxva2
--enable-iconv --enable-lzma --enable-nvenc --enable-zlib --enable-sdl2
--enable-ffnvcodec --enable-nvdec --enable-cuda-llvm --enable-libmp3lame
--enable-libopus --enable-libvorbis --enable-libx264 --enable-libx265
--enable-libdav1d --enable-libaom --disable-debug --enable-fontconfig
--enable-libass --enable-libbluray --enable-libfreetype --enable-libmfx
--enable-libmysofa --enable-libopencore-amrnb --enable-libopencore-amrwb
--enable-libopenjpeg --enable-libsnappy --enable-libsoxr --enable-libspeex
--enable-libtheora --enable-libtwolame --enable-libvidstab
--enable-libvo-amrwbenc --enable-libwebp --enable-libxml2 --enable-libzimg
--enable-libshine --enable-gpl --enable-avisynth --enable-libxvid
--enable-libopenmpt --enable-version3 --enable-libsrt --enable-libgsm
--enable-libvmaf --enable-libsvtav1 --enable-mbedtls
--extra-cflags=-DLIBTWOLAME_STATIC --extra-libs=-lstdc++
--extra-cflags=-DLIBXML_STATIC --extra-libs=-liconv --disable-w32threads
--shlibdir=/local64/bin-video
  libavutil      57.  0.100 / 57.  0.100
  libavcodec     59.  1.102 / 59.  1.102
  libavformat    59.  3.101 / 59.  3.101
  libavdevice    59.  0.100 / 59.  0.100
  libavfilter     8.  0.102 /  8.  0.102
  libswscale      6.  0.100 /  6.  0.100
  libswresample   4.  0.100 /  4.  0.100
  libpostproc    56.  0.100 / 56.  0.100
Input #0, lavfi, from 'mandelbrot':0KB vq=    0KB sq=    0B f=0/0
  Duration: N/A, start: 0.000000, bitrate: N/A
  Stream #0:0: Video: rawvideo (RGB[0] / 0x424752), rgb0, 640x480 [SAR 1:1
DAR 4:3], 25 tbr, 25 tbn
   1.24 M-V:  0.008 fd=   0 aq=    0KB vq=15600KB sq=    0B f=0/0

-steinar