Black becomes dark gray when converting rgb24 to gray16le

[Zsbán Ambrus]

Summary of the bug:

This bug is very similar to the fixed bug #2684, the difference is that we're using 16 bit depth output this time. I am using a newer version of ffmpeg that has #2684 fixed already.

When converting from rgb24 color space to gray16le colorspace, black input (represented as 0 0 0) becomes dary gray (represented as 4096) in the output.

How to reproduce:

I've tried this on windows 7 with the zeranoe build ffmpeg version N-60937-gb5005de built on Feb 26 2014 22:10:15 with gcc 4.8.2.

First, create a raw rgb24 input file with all zero contents, with the following command:

perl -we "binmode STDOUT; print pack q/x/.(3*16*16);" > zero-in-rgb.raw

Then invoke ffmpeg with the following command.

ffmpeg -report -v 99 -f rawvideo -pix_fmt rgb24 -s 16x16 -i zero-in-rgb.raw -f rawvideo -pix_fmt gray16le zero-out-gray16le.raw

Finally check the contents of the output with the following command.

perl -we "open F, q/</, shift or die; binmode F or die; local $/ = \(16*2); while (<F>) { print join(q/ /, unpack q/v*/, $_), qq/\n/; }" zero-out-gray16le.raw

The output shows the raw 16-bit little-endian words in the output, which should be all zero but isn't:

4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096
4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096 4096

Following is the log the ffmpeg command has saved.

ffmpeg started on 2014-02-27 at 11:57:27
Report written to "ffmpeg-20140227-115727.log"
Command line:
"E:\\ambrus\\local\\ffmpeg-20140227-git-b5005de-win64-shared\\bin\\ffmpeg.exe" -report -v 99 -f rawvideo -pix_fmt rgb24 -s 16x16 -i zero-in-rgb.raw -f rawvideo -pix_fmt gray16le zero-out-gray16le.raw
ffmpeg version N-60937-gb5005de Copyright (c) 2000-2014 the FFmpeg developers
  built on Feb 26 2014 22:10:15 with gcc 4.8.2 (GCC)
  configuration: --disable-static --enable-shared --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libcaca --enable-libfreetype --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-zlib
  libavutil      52. 66.100 / 52. 66.100
  libavcodec     55. 52.102 / 55. 52.102
  libavformat    55. 33.100 / 55. 33.100
  libavdevice    55. 10.100 / 55. 10.100
  libavfilter     4.  2.100 /  4.  2.100
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 18.100 /  0. 18.100
  libpostproc    52.  3.100 / 52.  3.100
Splitting the commandline.
Reading option '-report' ... matched as option 'report' (generate a report) with argument '1'.
Reading option '-v' ... matched as option 'v' (set logging level) with argument '99'.
Reading option '-f' ... matched as option 'f' (force format) with argument 'rawvideo'.
Reading option '-pix_fmt' ... matched as option 'pix_fmt' (set pixel format) with argument 'rgb24'.
Reading option '-s' ... matched as option 's' (set frame size (WxH or abbreviation)) with argument '16x16'.
Reading option '-i' ... matched as input file with argument 'zero-in-rgb.raw'.
Reading option '-f' ... matched as option 'f' (force format) with argument 'rawvideo'.
Reading option '-pix_fmt' ... matched as option 'pix_fmt' (set pixel format) with argument 'gray16le'.
Reading option 'zero-out-gray16le.raw' ... matched as output file.
Finished splitting the commandline.
Parsing a group of options: global .
Applying option report (generate a report) with argument 1.
Applying option v (set logging level) with argument 99.
Successfully parsed a group of options.
Parsing a group of options: input file zero-in-rgb.raw.
Applying option f (force format) with argument rawvideo.
Applying option pix_fmt (set pixel format) with argument rgb24.
Applying option s (set frame size (WxH or abbreviation)) with argument 16x16.
Successfully parsed a group of options.
Opening an input file: zero-in-rgb.raw.
[rawvideo @ 000000000061ba60] Before avformat_find_stream_info() pos: 0 bytes read:768 seeks:0
[rawvideo @ 000000000061ba60] All info found
[rawvideo @ 000000000061ba60] Estimating duration from bitrate, this may be inaccurate
[rawvideo @ 000000000061ba60] After avformat_find_stream_info() pos: 768 bytes read:768 seeks:0 frames:1
Input #0, rawvideo, from 'zero-in-rgb.raw':
  Duration: 00:00:00.04, start: 0.000000, bitrate: 153 kb/s
    Stream #0:0, 1, 1/25: Video: rawvideo (RGB[24] / 0x18424752), rgb24, 16x16, 1/25, 153 kb/s, 25 tbr, 25 tbn, 25 tbc
Successfully opened the file.
Parsing a group of options: output file zero-out-gray16le.raw.
Applying option f (force format) with argument rawvideo.
Applying option pix_fmt (set pixel format) with argument gray16le.
Successfully parsed a group of options.
Opening an output file: zero-out-gray16le.raw.
Successfully opened the file.
detected 4 logical cores
[graph 0 input from stream 0:0 @ 00000000004cec80] Setting 'video_size' to value '16x16'
[graph 0 input from stream 0:0 @ 00000000004cec80] Setting 'pix_fmt' to value '2'
[graph 0 input from stream 0:0 @ 00000000004cec80] Setting 'time_base' to value '1/25'
[graph 0 input from stream 0:0 @ 00000000004cec80] Setting 'pixel_aspect' to value '0/1'
[graph 0 input from stream 0:0 @ 00000000004cec80] Setting 'sws_param' to value 'flags=2'
[graph 0 input from stream 0:0 @ 00000000004cec80] Setting 'frame_rate' to value '25/1'
[graph 0 input from stream 0:0 @ 00000000004cec80] w:16 h:16 pixfmt:rgb24 tb:1/25 fr:25/1 sar:0/1 sws_param:flags=2
[format @ 00000000004ceac0] compat: called with args=[gray16le]
[format @ 00000000004ceac0] Setting 'pix_fmts' to value 'gray16le'
[auto-inserted scaler 0 @ 00000000004988a0] Setting 'flags' to value '0x4'
[auto-inserted scaler 0 @ 00000000004988a0] w:iw h:ih flags:'0x4' interl:0
[format @ 00000000004ceac0] auto-inserting filter 'auto-inserted scaler 0' between the filter 'Parsed_null_0' and the filter 'format'
[AVFilterGraph @ 000000000061fe00] query_formats: 4 queried, 2 merged, 1 already done, 0 delayed
[auto-inserted scaler 0 @ 00000000004988a0] w:16 h:16 fmt:rgb24 sar:0/1 -> w:16 h:16 fmt:gray16le sar:0/1 flags:0x4
Output #0, rawvideo, to 'zero-out-gray16le.raw':
  Metadata:
    encoder         : Lavf55.33.100
    Stream #0:0, 0, 1/90000: Video: rawvideo (Y1[0][16] / 0x10003159), gray16le, 16x16, 1/25, q=2-31, 200 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo -> rawvideo)
Press [q] to stop, [?] for help
[output stream 0:0 @ 00000000004cef20] EOF on sink link output stream 0:0:default.
No more output streams to write to, finishing.
frame=    1 fps=0.0 q=0.0 Lsize=       0kB time=00:00:00.04 bitrate= 102.4kbits/s    

video:0kB audio:0kB subtitle:0 data:0 global headers:0kB muxing overhead 0.000000%
1 frames successfully decoded, 0 decoding errors
[AVIOContext @ 000000000061b980] Statistics: 0 seeks, 1 writeouts
[AVIOContext @ 000000000061e8c0] Statistics: 768 bytes read, 0 seeks

[Carl Eugen Hoyos]

(The output of your perl script looks different here, what's wrong with hexdump?)

Could you test if attached patch fixes the issue for your usecase? The values are not 0 even with the patch...

[Carl Eugen Hoyos]

Were you able to test the patch I attached here?

[Carl Eugen Hoyos]

Should be fixed in 37c07d45

[Zsbán Ambrus]

The output has changed but is still not what I expect. Testing with the Zeranoe ffmpeg build for windows x64 "ffmpeg version N-61870-g62094e2 Copyright (c) 2000-2014 the FFmpeg developers built on Mar 26 2014 22:12:29 with gcc 4.8.2 (GCC)", using the commands in my report, I get the following output.

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

I expect all 0 values.

[Carl Eugen Hoyos]

Yes.

Why didn't you test before 2.2 was released?
Honestly: Bug reports are very important and very welcome but ignoring requests for testing probably doesn't help much motivating developers...

[Zsbán Ambrus]

Replying to cehoyos:

ignoring requests for testing probably doesn't help much motivating developers...

I'm sorry I didn't have time to contribute to this project.