[XviD-devel] Smoothening of the vector field

[Christoph Lampert]

Hi,

I just tested some GMC stuff and had to look at motion vectors for a
faster moving scene with only few textured blocks (beginning of DVD "Fifth
Element") The result looked horrible! Not only very long vectors (which is
okay for fast motion), but also very long "prediction corrections" (which
means the motion field is very irregular), and it's the corrections that
are saved to the bitstream and cost bits. :(

I would therefore like to see an option for smoothening the vector field 
after ME: In a second pass one tests for each MV if the current vector
really is that much better than the one of it's left and right neighbours. 
Somehow this is done in normal ME already, because search starts with
prediction of left, top and topright vectors. But that does not consider
blocks to the right and botto, of course. 
Also, there is also code that favours (0,0) in order to increase the
number of not_coded (SKIP) blocks. It seems that when there are large flat
areas, this causes the vector field to always skip between (0,0) and the
large vector of "real" motion. 

So again, either we have to _not_ favour SKIP during normal ME, and check
for more skip possibilities later (including the length of vectors that
_have_ to be coded, if the current block is skipped), or we leave ME as it
is and then remove SKIPs later when we know what the next vectors are
going to.

Comments?

gruel