[FFmpeg-trac] #9460(avfilter:closed): ssim only 0.47 while PSNR is 37, and skimage's result is 0.914

[FFmpeg]

#9460: ssim only 0.47 while PSNR is 37,  and skimage's result is  0.914
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             Reporter:  xmufzy      |                    Owner:  (none)
                 Type:  defect      |                   Status:  closed
             Priority:  normal      |                Component:  avfilter
              Version:  git-master  |               Resolution:  invalid
             Keywords:              |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
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Changes (by Elon Musk):

 * status:  reopened => closed
 * resolution:   => invalid

Comment:

 This is not support channel.
 The ssim algorithm are different, so you can not expect same results as
 python implementation.

 skimage converts to grayscale, you can do same with ffmpeg, if you learn
 how to do it:

 ffmpeg -i src0.png -i src1.png
 "[0:v]format=yuv444p[a];[1:v]format=yuv444p[b];[a][b]ssim" -f null -

 Even more if you extract each R/G/B component from src0.png and src1.png
 with -vf extractplanes=r+g+b and give each component image to skimage you
 get very similar low score.
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Ticket URL: <https://trac.ffmpeg.org/ticket/9460#comment:5>
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