Unexpected Color Conversion (bgr->yuv vs rgb->yuv)

[natt]

Input file is bgr24. Output file is yuv420p. If I instruct ffmpeg to convert to rgb24 first (instead of bgr24->yuv420p directly), the colors are slightly different.

Test input, exact command lines, and console output attached.

[natt]

output of testcase executable

[richardpl]

Whatever issue you are reporting I can not reproduce it.
rgb24(->bgr24)->yuv is fine here

[natt]

Replying to richardpl:

Whatever issue you are reporting I can not reproduce it.
rgb24(->bgr24)->yuv is fine here

The two conversions should be identical, right? Since rgb24<->bgr24 is lossless, bgr->rgb->yuv should produce the same output as bgr->yuv. If it doesn't, it's not working right.

ffmpeg -f rawvideo -video_size 256x256 -pix_fmt bgr24 -i testin.raw -sws_flags lanczos -f rawvideo -pix_fmt yuv420p md5:
0ba2a7494930baaa64869462d54b85cc

ffmpeg -f rawvideo -video_size 256x256 -pix_fmt bgr24 -i testin.raw -filter format=rgb24 -sws_flags lanczos -f rawvideo -pix_fmt yuv420p md5:
d5bd2d94675b67d23eb2661ca462966d

[cehoyos]

If there is an issue, is is reproducible with this command:

$ ./ffmpeg -i tests/lena.pnm -pix_fmt yuv420p -f crc - -vf format=bgr24 -pix_fmt yuv420p -f crc -
ffmpeg version N-37568-g8162c6f Copyright (c) 2000-2012 the FFmpeg developers
  built on Feb  5 2012 16:31:32 with gcc 4.5.3
  configuration: --cc='/usr/local/gcc-4.5.3/bin/gcc -m32'
  libavutil      51. 37.100 / 51. 37.100
  libavcodec     54.  0.102 / 54.  0.102
  libavformat    54.  0.100 / 54.  0.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 61.100 /  2. 61.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0.  6.100 /  0.  6.100
Input #0, image2, from 'tests/lena.pnm':
  Duration: 00:00:00.04, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: ppm, rgb24, 256x256, 25 tbr, 25 tbn, 25 tbc
[buffer @ 0x8dd20a0] w:256 h:256 pixfmt:rgb24 tb:1/1000000 sar:0/1 sws_param:
[buffersink @ 0x8dd2360] auto-inserting filter 'auto-inserted scale 0' between the filter 'src' and the filter 'out'
[scale @ 0x8dd28e0] w:256 h:256 fmt:rgb24 -> w:256 h:256 fmt:yuv420p flags:0x4
[buffer @ 0x8de20e0] w:256 h:256 pixfmt:rgb24 tb:1/1000000 sar:0/1 sws_param:
[buffersink @ 0x8de1780] auto-inserting filter 'auto-inserted scale 1' between the filter 'Parsed_format_0' and the filter 'out'
[format @ 0x8de0a80] auto-inserting filter 'auto-inserted scale 2' between the filter 'src' and the filter 'Parsed_format_0'
[scale @ 0x8df3960] w:256 h:256 fmt:rgb24 -> w:256 h:256 fmt:bgr24 flags:0x4
[scale @ 0x8de0b40] w:256 h:256 fmt:bgr24 -> w:256 h:256 fmt:yuv420p flags:0x4
Output #0, crc, to 'pipe:':
  Metadata:
    encoder         : Lavf54.0.100
    Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 256x256, q=2-31, 200 kb/s, 90k tbn, 25 tbc
Output #1, crc, to 'pipe:':
  Metadata:
    encoder         : Lavf54.0.100
    Stream #1:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 256x256, q=2-31, 200 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (ppm -> rawvideo)
  Stream #0:0 -> #1:0 (ppm -> rawvideo)
Press [q] to stop, [?] for help
CRC=0x7db3d981
CRC=0x74eb2924
frame=    1 fps=  0 q=0.0 Lq=0.0 size=       0kB time=00:00:00.04 bitrate=   3.0kbits/s
video:192kB audio:0kB global headers:0kB muxing overhead -99.992371%

[natt]

Replying to cehoyos:

If there is an issue, is is reproducible with this command:

Yes, I get exactly that.

>ffmpeg -i lena.pnm -pix_fmt yuv420p -f crc - -vf format=bgr24
-pix_fmt yuv420p -f crc -
ffmpeg version N-37541-g670229e Copyright (c) 2000-2012 the FFmpeg developers
  built on Feb  3 2012 20:07:47 with gcc 4.6.2
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-ru
ntime-cpudetect --enable-avisynth --enable-bzlib --enable-frei0r --enable-libope
ncore-amrnb --enable-libopencore-amrwb --enable-libfreetype --enable-libgsm --en
able-libmp3lame --enable-libopenjpeg --enable-librtmp --enable-libschroedinger -
-enable-libspeex --enable-libtheora --enable-libvo-aacenc --enable-libvo-amrwben
c --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-
libxvid --enable-zlib
  libavutil      51. 37.100 / 51. 37.100
  libavcodec     54.  0.102 / 54.  0.102
  libavformat    54.  0.100 / 54.  0.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 61.100 /  2. 61.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0.  6.100 /  0.  6.100
  libpostproc    52.  0.100 / 52.  0.100
Input #0, image2, from 'lena.pnm':
  Duration: 00:00:00.04, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: ppm, rgb24, 256x256, 25 tbr, 25 tbn, 25 tbc
[buffer @ 003DA880] w:256 h:256 pixfmt:rgb24 tb:1/1000000 sar:0/1 sws_param:
[buffersink @ 01B9D2A0] auto-inserting filter 'auto-inserted scale 0' between th
e filter 'src' and the filter 'out'
[scale @ 01B9D680] w:256 h:256 fmt:rgb24 -> w:256 h:256 fmt:yuv420p flags:0x4
[buffer @ 01B9DB20] w:256 h:256 pixfmt:rgb24 tb:1/1000000 sar:0/1 sws_param:
[buffersink @ 01C1CCA0] auto-inserting filter 'auto-inserted scale 1' between th
e filter 'Parsed_format_0' and the filter 'out'
[format @ 01C1BE40] auto-inserting filter 'auto-inserted scale 2' between the fi
lter 'src' and the filter 'Parsed_format_0'
[scale @ 01C1AAA0] w:256 h:256 fmt:rgb24 -> w:256 h:256 fmt:bgr24 flags:0x4
[scale @ 01C1BDE0] w:256 h:256 fmt:bgr24 -> w:256 h:256 fmt:yuv420p flags:0x4
Output #0, crc, to 'pipe:':
  Metadata:
    encoder         : Lavf54.0.100
    Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 256x256, q=2-31,
200 kb/s, 90k tbn, 25 tbc
Output #1, crc, to 'pipe:':
  Metadata:
    encoder         : Lavf54.0.100
    Stream #1:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 256x256, q=2-31,
200 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (ppm -> rawvideo)
  Stream #0:0 -> #1:0 (ppm -> rawvideo)
Press [q] to stop, [?] for help
CRC=0x7db3d981
CRC=0x74eb2924
frame=    1 fps=  0 q=0.0 Lq=0.0 size=       0kB time=00:00:00.04 bitrate=   3.0
kbits/s
video:192kB audio:0kB global headers:0kB muxing overhead -99.992371%