[FFmpeg-trac] #769(swscale:open): png gray8 alpha decodes incorrectly

[FFmpeg]

#769: png gray8 alpha decodes incorrectly
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             Reporter:  ami_stuff     |                    Owner:
                 Type:  defect        |                   Status:  open
             Priority:  normal        |                Component:  swscale
              Version:  git-master    |               Resolution:
             Keywords:  gray8a alpha  |               Blocked By:
             Blocking:                |  Reproduced by developer:  1
Analyzed by developer:  0             |
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Comment (by ami_stuff):

 I attache output from irfanview which I consider correct.

 Now please create these files:

 ffmpeg -loop 1 -t 5 -i basi4a08.png -vcodec rawvideo -pix_fmt rgba
 rgba.avi

 ffmpeg -loop 1 -t 5 -i basi4a08.png -vcodec rawvideo -pix_fmt yuv420p
 yuv420p.avi

 and play rgba.avi and yuv420p.avi with vlc.

 rgba.avi will look more or less ok (there are still some strange black
 dots - something like flipped "F", but let's ignore it for now).
 yuv420p.avi will have vertical black lines, which is not correct.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/769#comment:7>
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