[MPlayer-users] denoise3d and encoding DVD

[D Richard Felker III]

On Fri, Feb 07, 2003 at 08:19:37AM -0800, Corey Hickey wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> I've found that most of my DVD's have a certain high-resolution
> grainy-ness to them, and that by using the denoise3d filter like this:
> -vop scale=700:376,denoise3d,crop=716:480:2:0
> right after cropping and before scaling I can increase the PSNR
> somewhat. I've thrown a few short clips into the test, and it seems for
> high motion scenes the PSNR increases by about 0.5, whereas for low
> motion scenes the PSNR is raised by up to 2.

This is a bogus measurement. When lavc tells you the PSNR, the
"signal" it's comparing the encoded picture to is whatever you feed
into it, i.e. the already-filtered frames. Of course frames without as
much noise in them are going to encode better, but they won't
represent the original movie as well since some information was lost
in the filtering. If you could measure the PSNR relative to the
original picture, it would probably be worse with denoise3d.

On the other hand, that doesn't mean it's a bad idea to use denoise3d
for this. When you reduce the noise (which is likely not to be
perceptually important to a human viewer watching the movie), you'll
conserve bits which can then be used for more accurately encoding the
details you actually want to see.

My guess would be that denoise3d is probably a win in terms of
improving visual quality, at least in most cases, but PSNR is not a
good way of measuring whether or not it's a win. So if you really want
to check, you need to do double-blind tests with a group of viewers
and see which encode people identify as looking 'better'. Or else find
a good mathematical model for perceptual quality (good luck! ;).


Rich