[FFmpeg-devel] MJPG decoder picture quality

[Michael Niedermayer]

On Tue, Jun 08, 2010 at 03:46:16PM -0400, Pavel Pavlov wrote:
> I use libavcodec's jpeg decoder and I noticed that some pictures weren't looking good. Knowing that these pictures were meant to be very high quality, I decided to check out what was wrong.
> I couldn't find anything wrong, other that the fact that pictures that come out of libavcodec's MJPG decoder don't looks as good as they are supposed to.
> As a simple test I took a picture that comes from win7 install : 
> http://dev5.summit-tech.ca/pps/ffmpeg/Tulips.jpg
> Here's how this picture gets decoded by ffmpeg:
> http://dev5.summit-tech.ca/pps/ffmpeg/Tulips_yuv444.png

you need -sws_flags +accurate_rnd+full_chroma_int
the scalers defaults are tuned a bit toward realtime speed for video decoding.
This may arguably be something we should change for ffmpeg, iam not sure ...


> Here's doubled pixel compare image:
> http://dev5.summit-tech.ca/pps/ffmpeg/Tulips_compare_200.png (On the left, regular windows image viewer, on the right is MJPG from libavcodec)
> 
> I also saved raw yuv444: http://dev5.summit-tech.ca/pps/ffmpeg/Tulips_1024x768.yuv.bin
> Seems that ffplay can't open raw images (would be useful for development purposes), so I use yay.exe that can view raw yuv images: http://dev5.summit-tech.ca/pps/ffmpeg/yay.exe

-f rawvideo -pix_fmt yuv444p -s 1024x768 or something like that

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No snowflake in an avalanche ever feels responsible. -- Voltaire
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