[Ffmpeg-devel] upsampling of subsampled video data

[Attila Kinali]

On Sun, 10 Sep 2006 12:26:12 -0400
Rich Felker <dalias at aerifal.cx> wrote:

> > If it's interpolated, how much image quality los would it
> > be to just copy it?
> 
> Absolutely horrid. This is what the old matrox cards do with chroma
> for vertical scaling and it looks disgusting. You're a smart guy;
> throw in what you know about sampling theory and the fact that you're
> not dealing with "pixels" but samples and I'm sure you can realize for
> yourself how offensively wrong nearest-neighbor resampling is.

Well, it depends on how the data was prepared in the encoder.
That's why i asked.
 
> Most hardware does bicubic interpolation. Lanczos/sinc would be more
> theoretically correct but gauss is the most artifact-immune and also
> IMO the most theoretically correct since it's the only filter that's
> radially decreasing in both spatial and frequency domains. But
> probably anything more than bicubic is too expensive to do in
> hardware.

Actauly Bicubic is horribly expensive too. It's easy
to apply a convolution filter in horizontal direction
as you can just read out the data and pass it trough
a FIR or IIR filter. The problem comes from the second
dimension. The data has to be somehow stored and read
out again in a way that does not allow a fast burst read
but each pixel has to be adressed seperately which is a
hughe bandwidth los. Not to talk about the complexity
of the hardware.


			Attila Kinali

-- 
egp ist vergleichbar mit einem ikea bausatz fuer flugzeugtraeger
			-- reeler in +kaosu