[FFmpeg-devel] Fwd: Re: [Ffmpeg-user] jpg frame export : gama problem
Fri Jun 29 11:14:53 CEST 2007
On Thu, 21 Jun 2007 19:08:54 +0200, Nicolas Jauffret <nicolas at buf.fr>
> here is a discussion thread about a jpg export gama problem.
> Thank you for your time and support.
> Best regards,
> ------- Forwarded message -------
> From: "Nicolas Jauffret" <nicolas at buf.fr>
> To: "FFmpeg user questions and RTFMs" <ffmpeg-user at mplayerhq.hu>
> 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:
>>> 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
>>> ffmpeg doesn't seem to do a yuv level range conversion when exporting
>>> 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
> --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
> 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,
Have you well received my mail ?
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