[FFmpeg-trac] #8724(avfilter:new): chromakey does not observe existing transparency

[FFmpeg]

#8724: chromakey does not observe existing transparency
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             Reporter:  zerodefect   |                    Owner:
                 Type:  enhancement  |                   Status:  new
             Priority:  wish         |                Component:  avfilter
              Version:  git-master   |               Resolution:
             Keywords:  chromakey,   |               Blocked By:
  alpha                              |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by pdr0):

 Here is a workaround using blend on the alpha channel

 (using "gray" as the background and your chromkey arguments)

 {{{
 ffmpeg -f lavfi -i color=c=gray:s=640x400 -i green_screen4.png
 -filter_complex
 "[1:v]extractplanes=a[origa];[1:v]chromakey=color=0x00ff00:similarity=0.24:blend=0.01,format=gbrap,split[ckout1][ckout2];[ckout1]extractplanes=a[cka];[origa][cka]blend=all_mode=darken,format=gbrap[blend];[ckout2][blend]mergeplanes=0x00010210:gbrap[merge]"
 -map [merge] merge.png
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/8724#comment:5>
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