[MPlayer-users] Comparison of different software scaler types

[Matthias Wieser]

Am Mittwoch, 15. Oktober 2003 02:05 schrieb D Richard Felker III:
> On Tue, Oct 14, 2003 at 04:29:22PM +0200, Matthias Wieser wrote:
> > Results:
> > - sws 0    produces acceptable results
> > - sws 1    produces blurred images
> > - sws 2    produces very good images
> > - sws 7    is even worse than -sws 1
> > - sws 8    produces shadows near strong edges and increases contrast
> > - sws 9/10 produce the fewest artifacts and gives even a bit better
> >            results than -sws 2
>
> I looked at your pictures, and IMO you misunderstand what these are.
> There is no correct (much less no unique correct) way to scale images
> down.

I think, there is one.
A good downscaler should try to
 -preserve as much as possible details
- not introduce artifacts or noise (as -sws 8 does)
After scaling up, the difference to the original imige should be minimal.

If you want slightly blurred images, you could just use a gauss blur 
filter afterwards, or one of the special scaling filters like -sws 7.

I would say, -sws1 or -sws 7 are good filters,if you want to do two steps 
(scale and blur) at once, maybe because you do realtie encoding.

> If you want a better test, you should use MPlayer to scale the images
> *UP* with different filters, and then scale them back down and compare
> to the original.

Maybe I will test that, too.

But do you know, why -sws 8 is so broken? Sinc should produce very good 
quality (see
http://www.path.unimelb.edu.au/~dersch/interpolator/interpolator.html), 
but color and contrast should never be changed.

Are those heavy color changes, seen after more than one scaling, rounding 
errors?


Regards,
   Matthias