[FFmpeg-devel] MJPG decoder picture quality

Pavel Pavlov pavel
Wed Jun 9 01:59:11 CEST 2010

> -----Original Message-----
> bounces at mplayerhq.hu] On Behalf Of Baptiste Coudurier
> > 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
> This is weird, using this commandline:
> ffmpeg -i Tulips.jpg test%d.png
> with latest svn, I don't have the same png, the png I obtain have way more hot
> colors and looks exactly like the jpg.
> Btw the png is rgb24 not yuv444.
> Can you please share with us the ffmpeg commandline you are using ?

[Pavel Pavlov] 
I didn't use ffmpeg, I used avcodec. I tried doing it using ffmpeg -i Tulips.jpg test%d.png and I tried a downloadable ffmpeg build and I got the same results and in all cases images look the same.
By the way, I didn't notice any color differences between my image Tulips_yuv444.png, original Tulips.jpg and test%d.png, what color hotness differences do you get? Even if these images look the same, they really are far from the same; look closer: original image has perfect lines and the other two have some jagged edges and colors have some green or black in transition from yellow to red. My Tulips_yuv444.png is a bit different because it's actually yuvj444p rendered by sdl (yuv surface) and then I simply made a screenshot of the window :) yuv444 is the MJPG output for hi quality jpegs, has no relation to png of course.

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