[MPlayer-dev-eng] spp deblocking GREAT optimization !!!

[Nikolaj Poroshin]

Hello,

NP> You can get a 4-6x speedup of the SPP fiter by decomposing vert and
NP> horiz 1d dct/idct and decimating horizontal ones. This way, number of
NP> horiz passes will be 4 times for 4 & 5 levels, or 8 times for 6 level
NP> (which is rather useless, as noted in the original paper) lower.
NP> Vert passes are more suitable for optimization :)

NP> Next, you can use implied non-flat treshold with AAN dct w/o scale.
NP> (BTW, it is an interesing question - which treshold matrix provides
NP> best psnr?)

A futher explanation of the major point:

SPP deblocking is a series of 2D 8x8 dct->treshold->idct. For example,
at 6 (maximal) level, this is performed for all possible 8x8 block
locations, like row by row (or column by column), with step 1 both on X and Y. All results
of overlapping idct's are summed.

2D (i)dct (8x8) can be decomposed into horizontal & vertical passes of
1D (i)dct's. Lets take 1 column of SPP process:

-
- <(1) - <(2)
-      -
-      -
       -

Here "-" is a 1D horizontal dct8 pass. Its obvious, that results of
the (1) and (2) dct's are the same! (btw, not with all realizations).
This means decimation of horizontal 1D dct passes.

After vertical 1D dct ->treshold->idct (which I don't know how to
decimate :) ) :


==> -
==> -  +  - <==
==> -  +  - <==
==> -  +  - <==
          - <==

Here, "-" is a 1D horizontal Idct8 pass. "==>" and "<==" are the
'dataflows' from the vertical part. "+" is a sum of Idct8 passes and a
place, there the result is gets available. Due to Idct linearity,
"==> -  +  - <==" can be rewritten as

==> \
     +  -
==> /

(So, vert passes accumulates data for single horiz idct pass).
This means decimation of horizontal 1D Idct passes!

Personally I'd like to see & compare _different_ realization, since I
know, here exist great developers :) So, I rather give ideas, than
ready code. However, the code is ready - on the Celeron 633 SPP level
4 is fully working at the ~512x288 Divx film.

-- 
Regards,
 Nikolaj                          mailto:nialpof at pisem.net