[XviD-devel] Mode decision

[Christoph Lampert]

On 24 Mar 2003, skal wrote:
> > What you can't see, is how much a misclassification of INTER->INTER4V
> > or vice versa would cost in extra bits. 
> > And you also cannot see that there are hardly any real INTER4V blocks
> > with sad16 below 600. So maybe this would be a way to speed things up, 
> > simply not doing inter4v for those.
> 
> 	Even with a rather crude sad16-vs-sad8 final criterion for
> 	INTER/INTER4v decision, I've tried to guess whether a 16x16
> 	INTER block was worth a candidate for a sub 4V search (which
> 	takes times). I've tried some criterion based of local gradient
> 	and divergence (is the MV-field torn appart?), but it's not
> 	convincing. Actually, it seems that 4V works best at image's
> 	segmentation limits. So far, so good, I ended up with a sad
> 	-based criterion that is a good hint of whether going for a
> 	sub search might be rewarding: after a 16x16 regular search,
> 	I re-use the best MV found so far to evaluate sad8 of each of
> 	the four 8x8 sub blocks. If the maximum of these sad8 values 	is
> greater than a fraction the sad16 for the full block
> 	(in practice 60% is a good compromise), then I go for a
> 	refined search...
> 
> 	Any opinion?

Yes, it might be possible to check earlier if INTER4V is promising
(INTER is already very good => no, SAD8 very different => yes).
I had plans using that current search also find best positions and
SADs so far for the 8x8 blocks during search for 16x16.  But my results
were not convincing.

If yours is better, great! Do you have results? 

gruel