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Hi Steinar, Thomas,

I saw your new constrained low pass filter draft for Thor and decided
to start experimenting with it. Putting the filter in Daala, I saw a
PSNR bd-rate improvement around 2.1% in the 0.05 bpp to 0.1 bpp range
over our ntt-short1 test set (I disabled our deringing filter for this
comparison to avoid the interactions). However, I was unable to see
improvements of 4-7% like you are reporting in the draft.

Of course, it's quite likely that I messed up the implementation or
the adaptation to Daala. It's also possible that somehow Daala cannot
benefit from the CLP as much as Thor does. This is the code I wrote
for filtering a small block of pixels:
https://pastebin.mozilla.org/8850049
I've had to do some adaptation since the Daala pixels are shifted up
by 4 at the point where we're applying the filter. Does this look
correct to you?

The other experiment that would be nice to try is using the Daala
deringing filter in Thor. In Daala, our deringing filter is improving
PSNR bd-rate by about a 6.5% in the 0.05 bpp to 0.1 bpp range. The
deringing filter is documented in this IETF draft:
https://tools.ietf.org/html/draft-valin-netvc-deringing-00
or (for those who don't like ASCII equations) in this pdf:
http://jmvalin.ca/notes/dir_dering.pdf
I uploaded some still image examples at:
http://jmvalin.ca/video/deringing_examples/
Any interest in trying the Daala deringing filter in Thor?

Cheers,

        Jean-Marc
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