[XviD-devel] EDGE_SIZE == 64

suxen_drol suxen_drol at hotmail.com
Mon Mar 10 10:23:30 CET 2003


On Sun, 9 Mar 2003 17:44:57 +0100 (CET) Christoph Lampert <chl at math.uni-bonn.de> wrote:

> I'm sure this was asked before, but: Why is EDGE_SIZE defined 
> as 64 in image/image.h? That's far beyond what is needed for
> unrestricted motion vectors. 16 should be sufficient for this, or not? 


EDGE_SIZE was originally set to 32 because we need an additional 16
pixels on each side of the image for unresticted mvs.
EDGE_SIZE reflects 16+16. EDGE_SIZE2 reflects 16.


EDGE_SIZE was increased to 64 to accomdate quarterpel. qpel filters may
need to access upto 3 pixels (i think...) outside the unrestricted range.

notes:
* we could use 48 instead of 64, and still maintain 16-byte stride alignment
* we dont need to setedges the entire EDGE_SIZE, only the 16+3 pixels
per side. 

-- pete; life is like a box of ammo




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