[XviD-devel] Re: qpel smearing/noise problem

[Michael Niedermayer]

Hi

On Thursday 09 January 2003 13:19, Radek Czyz wrote:
[...]
> Does anyone remember where can I find in the specs, what size of block
> is used for halfpel interpolation in qpel mode? I've been doing all my
> experiments both on 8x8 blocks and 16x16 blocks, simply because I don't
> know which is correct. I'v been looking for it, but I havn't found the
> answer.
for 1MV the lowpass filter is done on a 17x17 block with the boundary mirrored
for 4MV its done on 9x9 block with the boundary mirrored

all just IMHO ...

AFAIK, the reason behind this weird boundary mirroring is btw, to reduce the 
memory bandwidth needed for fetching the blocks in hardware implementations

the number of fetched bytes for
1mv with mirroring    17x17  = 289
1mv without mirroring 23x23  = 529
4mv with mirroring    9 x 9x4= 324 
4mv without mirroring 15x15x4= 900 
so its quite significant worst case reduction

[...]

Michael