[FFmpeg-trac] #9750(avfilter:new): overlay filter alpha premultiplied performs brighter on transparent images

[FFmpeg]

#9750: overlay filter alpha premultiplied performs brighter on transparent images
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             Reporter:  windowsair  |                    Owner:  (none)
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  avfilter
              Version:  git-master  |               Resolution:
             Keywords:              |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
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Comment (by windowsair):

 Let's first focus on the RGBA file "a.hex" as rawvideo input. (I have
 uploaded that before)

 1. get the expected output:

 {{{
 ffmpeg.exe  -i a1.mp4 -f rawvideo -s 1920x540 -pix_fmt rgba -i a.hex
 -filter_complex
 "[0:v][1:v]overlay=x=0:y=0:alpha=premultiplied:format=rgb[v]" -map "[v]"
 -c:v:0 libx264 -f mp4  output.mp4
 }}}

 2. get the wrong output (black becomes bright)

 {{{
 ffmpeg.exe  -i a1.mp4 -f rawvideo -s 1920x540 -pix_fmt rgba -i a.hex
 -filter_complex
 "[0:v][1:v]overlay=x=0:y=0:alpha=premultiplied:format=yuv420[v]" -map
 "[v]"  -c:v:0 libx264 -f mp4  output.mp4
 }}}


 Maybe, as you said, there is a loss of accuracy in the different pixel
 format conversions.

 But when I first set the output format of overlay to rgb and then convert
 it back to yuv420p, I get the correct output as expected. I use the
 following command:
 {{{
 ffmpeg.exe  -i a1.mp4 -i imagename.png -filter_complex
 "[0:v][1:v]overlay=x=0:y=0:format=rgb:alpha=premultiplied[v0];[v0]format=yuv420p[v]"
 -map "[v]"  -c:v:0 libx264 -f mp4  output.mp4
 }}}

 Sorry, I don't know anything about FFmpeg. Hope this helps!
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Ticket URL: <https://trac.ffmpeg.org/ticket/9750#comment:9>
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