[Ffmpeg-devel] [PATCH] DV image quality improvement

[Michael Niedermayer]

Hi

On Mon, Feb 27, 2006 at 07:15:58AM -0500, Dan Maas wrote:
> > I have nothing against having this alternative method for assigning 
> > class numbers, but I would like to 
> > suggest one thing: could you, please, make it easy to switch 
> > between the two versions of how classes are assigned ? 
> 
> See attached... I've rewritten the patch so that it's just a one-line
> change from the SMPTE method.
> 
> I also included the new checksums. The PSNR increase on ffmpeg's test
> video is from 29.03 to 29.17. The impact on natural-looking live video
> is more dramatic - the 4825-frame BBC test video (all live scenes)
> goes up from 41.77 to 44.72 with my adjustment (in DV50 mode - patch
> forthcoming).
> 
> > I completely agree with you here. In fact, when I was developing DV encoder 
> > the quantization step table (on page 37) made me very puzzled. It is quite
> > obvious to anyone that having just two class numbers 2 and 3 is enough
> > to cover *all* possible cases of quantization
> 
> Class number is per-block, whereas QNO is per-macroblock. A really
> sophisticated encoder could optimize class numbers together with QNO
> to squeeze out every last bit of efficiency. Of course, that would
> come at a huge cost in CPU time.
> 
> On the bright side, I've looked at a lot of DV encoders, and most of
> them don't even come close to the sophistication of ffmpeg's. For
> instance, my $1500 Canopus ADVC-500 hardware encoder assigns a fixed
> QNO to almost all blocks, and performs quantization very coarsely by
> playing with class numbers. Only Apple's encoder seems to make an
> attempt of optimizing both class numbers and QNO. But it's still more
> conservative than ffmpeg in QNO assignment, so the results aren't
> necessarily better. With this class-number patch, ffmpeg's output is
> roughly equal in image quality to the Apple encoder. (no small feat,
> as Apple's is one of the best, if not the best one out there)

if you care so much about quality, then maybe you want to implement trellis
quantization for dv, see dct_quantize_trellis_c()

[...]

-- 
Michael