#9195: vibrance (video filter) incorrect defaults for luma -------------------------------------+------------------------------------- Reporter: Jim | Type: defect DeLaHunt | Status: new | Priority: normal Component: avfilter | Version: git- | master Keywords: | Blocked By: Blocking: | Reproduced by developer: 0 Analyzed by developer: 0 | -------------------------------------+------------------------------------- Summary of the bug: The "vibrance" video filter appears to have incorrect default values for the luma coefficient parameters "rlum" and "blum". They appear to be swapped. How to reproduce: {{{ % ffmpeg -h filter=vibrance ffmpeg version 4.4 Copyright (c) 2000-2021 the FFmpeg developers built with Apple LLVM version 10.0.0 (clang-1000.10.44.4) configuration: --prefix=/opt/local --enable-swscale --enable-avfilter --enable-avresample --enable-libmp3lame --enable-libvorbis --enable- libopus --enable-librsvg --enable-libtheora --enable-libopenjpeg --enable- libmodplug --enable-libvpx --enable-libsoxr --enable-libspeex --enable- libass --enable-libbluray --enable-lzma --enable-gnutls --enable- fontconfig --enable-libfreetype --enable-libfribidi --disable-libjack --disable-libopencore-amrnb --disable-libopencore-amrwb --disable- indev=jack --enable-opencl --disable-outdev=xv --enable-audiotoolbox --enable-videotoolbox --enable-sdl2 --disable-securetransport --mandir=/opt/local/share/man --enable-shared --enable-pthreads --cc=/usr/bin/clang --enable-libdav1d --arch=x86_64 --enable-x86asm --enable-libx265 --enable-gpl --enable-postproc --enable-libx264 --enable- libxvid libavutil 56. 70.100 / 56. 70.100 libavcodec 58.134.100 / 58.134.100 libavformat 58. 76.100 / 58. 76.100 libavdevice 58. 13.100 / 58. 13.100 libavfilter 7.110.100 / 7.110.100 libavresample 4. 0. 0 / 4. 0. 0 libswscale 5. 9.100 / 5. 9.100 libswresample 3. 9.100 / 3. 9.100 libpostproc 55. 9.100 / 55. 9.100 Filter vibrance Boost or alter saturation. slice threading supported Inputs: #0: default (video) Outputs: #0: default (video) vibrance AVOptions: intensity <float> ..FV.....T. set the intensity value (from -2 to 2) (default 0) rbal <float> ..FV.....T. set the red balance value (from -10 to 10) (default 1) gbal <float> ..FV.....T. set the green balance value (from -10 to 10) (default 1) bbal <float> ..FV.....T. set the blue balance value (from -10 to 10) (default 1) rlum <float> ..FV.....T. set the red luma coefficient (from 0 to 1) (default 0.072186) glum <float> ..FV.....T. set the green luma coefficient (from 0 to 1) (default 0.715158) blum <float> ..FV.....T. set the blue luma coefficient (from 0 to 1) (default 0.212656) alternate <boolean> ..FV.....T. use alternate colors (default false) This filter has support for timeline through the 'enable' option. }}} The vibrance filter is documented at https://ffmpeg.org/ffmpeg- filters.html#vibrance . It looks like coefficients "rlum", "glum", and "blum" are supposed to match the luma computation as defined in BT.709-6 (https://en.wikipedia.org/wiki/Rec._709) or something similar. Wikipedia gives this formula as:

R’G’B’ coefficients 0.2126, 0.7152, and 0.0722 (together they add to 1)

So, `luma = 0.2126 * r + 0.7152 * g + 0.0722 * b`, a value in [0.0, 1.0] for r, g, b in [0.0, 1.0] But the default values I see in the FFmpeg vibrance filter are (per output above):

rlum (default 0.072186), glum (default 0.715158), blum (default 0.212656)

Thus it looks like the default values for rlum and blum are swapped. Vibrance would still compute a luma a value in a range of [0.0, 1.0], but it wouldn't be the correct value per BT.709. Since the vibrance adjustments are relative to luma, they might be slightly off. I believe the fix would be the simple, obvious exchange of default values in ffmpeg/libavfilter/vf_vibrance.c:372-374. But I haven't tried this. Present code: {{{ { "rlum", "set the red luma coefficient", OFFSET(lcoeffs[2]), AV_OPT_TYPE_FLOAT, {.dbl=0.072186}, 0, 1, VF }, { "glum", "set the green luma coefficient", OFFSET(lcoeffs[0]), AV_OPT_TYPE_FLOAT, {.dbl=0.715158}, 0, 1, VF }, { "blum", "set the blue luma coefficient", OFFSET(lcoeffs[1]), AV_OPT_TYPE_FLOAT, {.dbl=0.212656}, 0, 1, VF }, }}} Code with possible fix: {{{ { "rlum", "set the red luma coefficient", OFFSET(lcoeffs[2]), AV_OPT_TYPE_FLOAT, {.dbl=0.212656}, 0, 1, VF }, { "glum", "set the green luma coefficient", OFFSET(lcoeffs[0]), AV_OPT_TYPE_FLOAT, {.dbl=0.715158}, 0, 1, VF }, { "blum", "set the blue luma coefficient", OFFSET(lcoeffs[1]), AV_OPT_TYPE_FLOAT, {.dbl=0.072186}, 0, 1, VF }, }}} -- Ticket URL: <https://trac.ffmpeg.org/ticket/9195> FFmpeg <https://ffmpeg.org> FFmpeg issue tracker