[FFmpeg-trac] #8588(avfilter:closed): Palettegen adds one color on transparent input

[FFmpeg]

#8588: Palettegen adds one color on transparent input
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             Reporter:  RedError     |                    Owner:
                 Type:  defect       |                   Status:  closed
             Priority:  normal       |                Component:  avfilter
              Version:  git-master   |               Resolution:  invalid
             Keywords:  palettegen   |               Blocked By:
  alpha                              |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by RedError):

 Replying to [comment:7 cehoyos]:
 > But the filter is not gif-only.
 And? The gif discussion was only how I got to that conclusion. The fix
 doesn't make any assumption about the input being a gif.
 >The solution is to not call color_inc if p[x]'s alpha is zero.
 This applies to PNG and GIF and any format that has Alpha/transparency.
 For any of those, if the color has an alpha of Zero, the user doesn't
 expect it to appear in the palette.

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Ticket URL: <https://trac.ffmpeg.org/ticket/8588#comment:8>
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