[XviD-devel] trellis questions
skal
skal at planet-d.net
Sat Sep 11 07:33:27 CEST 2004
Hi Syskin and all,
On Sat, 2004-09-04 at 14:00, Radek Czyz wrote:
> Hi everyone,
>
> I'm still breaking trellis search :) and I have a question:
>
> There is a code
>
> /* source (w/ CBP penalty) */
> Run_Costs[-1] = 2<<TL_SHIFT;
>
> As far as I understand, it's an approximation of CBP cost - but I have
> absolutely no idea how it works... so, how?
It's really a rough approximation, based on few
experimentations. This pseudo-cost associated to
the node -1 is just an artificial barrier to overcome
when any coeff gets coded at all.
> Also, how do I change the code if the block is initially empty and I'm
> running trellis anyway? (IF I do that. if.)
>
> Or maybe CBP is just not taken into account?
Sure, the real CBP is not taken into account.
We only evaluate the save for not coding a
block as 2 bits/block, on average.
(maybe the real value is a little lower, btw).
bye!
Skal
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