[MPlayer-users] Re: [POOL] Moderate some users (was: Re: [-] Re: divx 6)

[Rich Felker]

On Sat, May 06, 2006 at 10:19:41PM +0400, Vladimir Mosgalin wrote:
> PSNR PROVES NOTHING.
> 
> Now read this again as many times as you need to remember it.
> 
> 0.1 dB improvement - I can only laugh at that. Even 0.5 dB difference in
> PSNR doesn't mean that one of the encoded version looks better.
> 
> For example, why do you use mpeg_quant? It improves quality, but very
> often reduces psnr.
> 
> I've seen so many cases when psnr and my eye tell me opposite, so now I
> don't even try to compare psnr. In some cases quality difference is
> obvious at the first sight, in other cases you need to look harder, but
> that's exactly when psnr starts to fail too.

Provided you only change certain parameters, psnr can be a good
comparison to tell you whether changes to the codec improved quality
or made it worse. However like you say there are many parameters (like
changing the quantization) that changes the game entirely. Here's a
good example for anyone who worships psnr:

http://www.cns.nyu.edu/~zwang/files/research/quality_index/demo_lena.html

Rich