[Ffmpeg-devel-old] Re: [Ffmpeg-devel] Snow motion blocks

[Rich Felker]

On Mon, Apr 18, 2005 at 09:20:46PM +0300, Tuukka Toivonen wrote:
> >	Details at: http://skal.planet-d.net/coding/interpolation.html
> 
> Ah. Finally I understand, I hope, your paper main idea. So you
> generalize half-pixel linear interpolation into "infinite resolution"
> linear interpolation, compute analytically the optimum MV in this
> infinite resolution, and then round it to the nearest
> half- or integer pixel location.
> 
> Interesting idea. I actually found your page when I was looking
> for material for my paper, but back then I didn't quite understand it.
> 
> Might work nicely if newer standards such as H.264 would use
> linear interpolation for fractional pixel interpolation, but as they don't, 
> the methods are less useful :(

I haven't been following this discussion, but I'd be very interested
in replacing snow's motion comp with linear interpolation if empirical
results turn out to be good. The higher order interpolation we're
using now is much slower, and since it's effectively a sharpening
filter, it probably adds artifacts that make it more difficult for the
wavelet transform to encode the residue efficiently (i.e. more
high-frequency coefficients).

My naive guess would be that higher-order motion comp has effects
similar to mpeg_quant for mpeg4 encoding, i.e. improved psnr at very
low quantizers, but worse quality (esp. worse artifacts) at higher
quantizers. Unless removing it makes low-quant snow a LOT better at
compression, I think the speed issue is enough to put me strongly in
favor of using linear interp. But I'd like to hear more points on all
sides.

Rich