[XviD-devel] Interview with Gej, mentioning XviD
Radek Czyz
syskin at ihug.com.au
Mon Mar 22 13:24:21 CET 2004
Christoph Lampert wrote:
> I know you know this, but maybe somebody else is interested, too:
>
> In theory, distorsion D of R+lambda*D is already quadratic (it's
> sum-of-squared quantization error). The rate R includes bits for
> vector as well as bits for coding of quantized coefficients.
As an electrical engineer (more or less), I prefer to see
sum-of-squared-stuff as energy (just linear energy). But sure, there was
one square involved.
> To speed this us, it is only approximated by R + lambda*D with
> R = vector bits and D=SAD (and different lambda), and there, the
> SAD somehow compensates that the coefficient bits aren't taken into
> account. Usually, SAD doesn't tell anything about PSNR, because it's
> calculated before the reconstructed images (from quant/dequantized DCT
> coefficient) is subtracted from current.
Okay yes, but I was talking about VHQ mode decison and ME. I'm also
thinking how to repeat this step for trellis quantization, but I'm not
even trying to implement that one.
> If you find a combination that works better, hey, that would be great. The
> problem might be how to "measure" is, because PSNR won't help there.
That's right.... The minimum PSNR (across all frames) would rise, but it
would rather be a side-effect - the idea wouldn't really work on whole
frames but on blocks - and I haven't seen "minimum block PSNR in given
frame" yet.
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