[FFmpeg-devel] ffmpeg gama problem (Was: Fwd: Re: [Ffmpeg-user] jpg frame export : gama problem)

[Nicolas Jauffret]

Hello,

On Wed, 11 Jul 2007 15:01:58 +0200, Nicolas Jauffret <nicolas at buf.fr>  
wrote:

> Hi,
>
> On Wed, 04 Jul 2007 15:23:17 +0200, Nicolas Jauffret <nicolas at buf.fr>
> wrote:
>
>> Hi
>>
>> On Fri, Jun 29, 2007 at 11:14:53AM +0200, Nicolas Jauffret wrote:
>>> On Thu, 21 Jun 2007 19:08:54 +0200, Nicolas Jauffret <nicolas at  
>>> buf.fr> wrote:
>>>> Hello,
>>> > here is a discussion thread about a jpg export gama problem.
>>> > Thank you for your time and support.
>>> > Best regards,
>>> >
>>> > Nick
>>> >
>>> > ------- Forwarded message -------
>>> > From: "Nicolas Jauffret" <nicolas at buf.fr>
>>> > To: "FFmpeg user questions and RTFMs" <ffmpeg-user at mplayerhq.hu>
>>> > Cc:
>>> > Subject: Re: [Ffmpeg-user] jpg frame export : gama problem
>>> > Date: Thu, 21 Jun 2007 18:58:17 +0200
>>> >
>>> > On Thu, 21 Jun 2007 18:08:44 +0200, Michel Bardiaux
>>> > <mbardiaux at mediaxim.be> wrote:
>>> >
>>> >> Nicolas Jauffret wrote:
>>> >>> Hello,
>>> >>>
>>> >>> When I try to extract a frame from a dv video with this command :
>>> >>>
>>> >>>    ffmpeg -i "input.mov" -vframes 1 -ss 0.0000 -t 0.0400  
>>> "out.%08d.jpg"
>>> >>
>>> >> You should always post the complete output messages too.
>>> >>
>>> >>>
>>> >>> I have a gama problem : the initial black RGB(0,0,0) becomes >>>  
>>> RGB(16,16,16).
>>> >>> ffmpeg doesn't seem to do a yuv level range conversion when  
>>> exporting >>> to
>>> >>> jpeg.
>>> >>>
>>> >>>
>>> >>> If I choose png file format for output, I have no problem.
>>> >>> I get a pure black RGB(0,0,0) in my exported frame.
>>> >>>
>>> >>>    ffmpeg -i "input.mov" -vframes 1 -ss 0.0000 -t 0.0400  
>>> "out.%08d.png"
>>> >>>
>>> >>
>>> >> If only a few pixels of that image are black, well, JPEG is lossy,  
>>> so
>>> >> its no surprise it takes liberties with some pixels. Make an  
>>> all-black
>>> >> image as a BMP or raw or other lossless format, and convert it to  
>>> JPEG
>>> >> with ffmpeg. If still not black, then report the bug.
>>> >
>>> > Of course, I have done that with a black images test sequence.
>>> >
>>> > I confirm that there is a problem doing this:
>>> >
>>> > $ ffmpeg -i input.bmp -f image2 output.%d.jpg
>>> > FFmpeg version SVN-r9377, Copyright (c) 2000-2007 Fabrice Bellard,  
>>> et al.
>>> >     configuration: --enable-gpl --enable-static --enable-swscaler
>>> > --enable-pthreads --enable-libmp3lame --enable-libogg  
>>> --enable-libxvid
>>> > --disable-ffserver --enable-memalign-hack --enable-libx264 >  
>>> --enable-liba52
>>> > --extra-ldflags=-l m
>>> >     libavutil version: 49.4.0
>>> >     libavcodec version: 51.40.4
>>> >     libavformat version: 51.12.1
>>> >     built on Jun 21 2007 16:36:33, gcc: 3.3.5 (Debian 1:3.3.5-13)
>>> > Input #0, image2, from 'input.bmp':
>>> >     Duration: 00:00:00.0, start: 0.000000, bitrate: N/A
>>> >     Stream #0.0: Video: bmp, bgr24, 420x300, 25.00 fps(r)
>>> > Output #0, image2, to 'output.%d.jpg':
>>> >     Stream #0.0: Video: mjpeg, yuvj420p, 420x300, q=2-31, 200 kb/s,  
>>> 25.00
>>> > fps(c)
>>> > Stream mapping:
>>> >     Stream #0.0 -> #0.0
>>> > Press [q] to stop encoding
>>> > Compiler did not align stack variables. Libavcodec has been  
>>> miscompiled
>>> > and may be very slow or crash. This is not a bug in libavcodec,
>>> > but in the compiler. Do not report crashes to FFmpeg developers.
>>> > frame=    1 fps=  0 q=3.5 Lsize=       0kB time=0.0 bitrate=    
>>> 0.0kbits/s
>>> > video:3kB audio:0kB global headers:0kB muxing overhead -100.000000%
>>> >
>>> > Although, the "input.bmp" is a full black RGB(0,0,0) image,
>>> > the "output.1.jpg" is not black : RGB(16,16,16).
>>> >
>>> > I am going to report this issue to the devel mailing list.
>>> > Best regards,
>>> >
>>> > Nick
>>> Ping ?
>>> Have you well received my mail ?
>>
>> yes and patch welcome, its likely a problem with the colorspace  
>> convertion
>> see sws_setColorspaceDetails() and the code responsible for RGB->YUV
>
> I won't be able to patch it, but found similar problems when compressing
> from jpeg image sequences.
>
> There are some strange gama differences when compressing from a jpg  
> images
> sequence or a png images sequence.
>
> I made a test example and wrote a detailed README file to go with.
> You can find these in the mplayer FTP repository :
>
>     upload.mplayerhq.hu:/MPlayer/incoming/gama_problem
>
> Thank you for your time and support,

Have you had time to check out my test files ?
It seems like an overall gama conversion problem.
Regards,

Nick