[FFmpeg-trac] #3795(swscale:new): SWSCALE: Quantization Errors in Y Studio Range

FFmpeg trac at avcodec.org
Wed Jul 23 05:51:43 CEST 2014


#3795: SWSCALE: Quantization Errors in Y Studio Range
------------------------------------+--------------------------------------
             Reporter:  troy_s      |                     Type:  defect
               Status:  new         |                 Priority:  normal
            Component:  swscale     |                  Version:  git-master
             Keywords:  709 Y luma  |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
------------------------------------+--------------------------------------
 Summary of the bug:

 It appears FFMPEG has some +/- single unit quantization errors in the
 YCbCr transform.

 How to reproduce:

 Generate a raw YCbCr image and diff against theoretically correct values.
 {{{
 ./ffmpeg -i ~/Documents/FFMPEG\ Color\ Research/ARIB_STD-B28.png -pix_fmt
 yuv444p -vcodec rawvideo -f rawvideo -vf
 scale="in_range=full:in_color_matrix=bt709:out_range=full:out_color_matrix=bt709"
 test.yuv
 ffmpeg version N-64815-gb53bdae Copyright (c) 2000-2014 the FFmpeg
 developers
   built on Jul 19 2014 16:33:49 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
   configuration: --enable-gpl --enable-libx264 --disable-asm
   libavutil      52. 92.101 / 52. 92.101
   libavcodec     55. 69.100 / 55. 69.100
   libavformat    55. 48.101 / 55. 48.101
   libavdevice    55. 13.102 / 55. 13.102
   libavfilter     4. 11.102 /  4. 11.102
   libswscale      2.  6.100 /  2.  6.100
   libswresample   0. 19.100 /  0. 19.100
   libpostproc    52.  3.100 / 52.  3.100
 Input #0, image2, from '/home/aphorism/Documents/FFMPEG Color
 Research/ARIB_STD-B28.png':
   Duration: 00:00:00.04, start: 0.000000, bitrate: N/A
     Stream #0:0: Video: png, rgb24, 1920x1080 [SAR 2835:2835 DAR 16:9], 25
 tbr, 25 tbn, 25 tbc
 Output #0, rawvideo, to 'test.yuv':
   Metadata:
     encoder         : Lavf55.48.101
     Stream #0:0: Video: rawvideo (444P / 0x50343434), yuv444p, 1920x1080
 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 25 fps, 25 tbn, 25 tbc
     Metadata:
       encoder         : Lavc55.69.100 rawvideo
 Stream mapping:
   Stream #0:0 -> #0:0 (png (native) -> rawvideo (native))
 Press [q] to stop, [?] for help
 frame=    1 fps=0.0 q=0.0 Lsize=    6075kB time=00:00:00.04
 bitrate=1244160.0kbits/s
 video:6075kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: 0.000000%
 }}}

 Diff'd versions of the theoretically ideal values versus FFMPEG's output.
 Lowest red stripe is due to theoretical version preserving the -2% patch,
 and not relevant.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/3795>
FFmpeg <https://ffmpeg.org>
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