[FFmpeg-devel] Issues with ljpeg

[Mathieu Malaterre]

A couple of comments on ljpeg encoder:

1. (minor) There is no such thing as Ss=8 in JPEG lossless.

 $ ffmpeg -f image2 -i beach.jpg -f image2 -pred 7 -vcodec ljpeg
/tmp/out0.ljpeg

As far as I under the code when pred is > 7 then predictor=7 is used
(see PREDICT macro in mjpeg.h). But Ss=8 is stored in the jpeg header.

2. A more serious issue is for pred=4, pred=5 and pred=6. I made some
snapshots of what I can see using IJG decompressor (+lossless patch)
here:

http://jpeg.sourceforge.net/ffmpeg/

  Using the following command lines:

./ffmpeg -f image2 -i beach.jpg -f image2 -pred 6 -vcodec ljpeg  /tmp/out6.ljpeg
./ffmpeg -f image2 -i beach.jpg -f image2 -pred 5 -vcodec ljpeg  /tmp/out5.ljpeg
./ffmpeg -f image2 -i beach.jpg -f image2 -pred 4 -vcodec ljpeg  /tmp/out4.ljpeg

Sorry I could not find the issue, but if anyone understand where the
issue could be coming from, I volunteer to prepare the patch.

Thanks,
-- 
Mathieu