[MEncoder-users] Help understand SSIM

[Matyas]

I did an encode at crf=1.  I used cropping, yadif, hqdn3d and scaling.
Mencoder printed the mean SSIM as: 0.9944191.

My question is what does the above SSIM measure?  What are the two frames
compared?  I thought that crf=1 will result in lossless encoding *after*" the
filters applied.  Correct me please if I am wrong in this assumption.  (The
doc says qp=0 is lossless and that crf has similar scale and the lowest
possible value is 1.0.)

I assume that the effect of denoising, deinterlacing etc. is not captured by
the reported SSIM.  So why does the SSIM do not equal to 1?

How cropping and scaling affect the SSIM calculation used in mencoder?

Thanks!
Matyas
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