[FFmpeg-trac] #9872(undetermined:new): WebP vs PNG alpha

[FFmpeg]

#9872: WebP vs PNG alpha
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             Reporter:  Jozef        |                    Owner:  (none)
  Chutka                             |
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  unspecified  |               Resolution:
             Keywords:  scale alpha  |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by Jozef Chutka):

 After some more testing (and updated .webp and .png exports from my
 graphic program) it appears the issue not related to webp or pixel format
 itself, but rather related to the RGB values of the semi-transparent pixel
 and scale filter. While the shape edge is rendered correctly without scale
 filter used, once `scale` is used, the alpha of the edge pixels gets
 "premultiplied".
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Ticket URL: <https://trac.ffmpeg.org/ticket/9872#comment:6>
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