[FFmpeg-devel] Rework color quantization in palette{gen,use}

[Clément Bœsch]

On Sun, Nov 06, 2022 at 06:30:22PM +0100, Michael Niedermayer wrote:
> On Sun, Nov 06, 2022 at 06:09:41PM +0100, Michael Niedermayer wrote:
> > On Sat, Nov 05, 2022 at 04:26:02PM +0100, Clément Bœsch wrote:
> > > Hi,
> > > 
> > > This patchset essentially fixes a few core problems in these filters and
> > > switches to a perceptual model.
> > > 
> > > I've generated a report for each key commit on this (temporary) page:
> > > http://big.pkh.me/pal/ (warning: heavy page, ~500M; I did try to add some lazy
> > > loading of the images but I'm not sure it's actually working as expected).
> > 
> > i just looked at file00 and 16 and 64 colors with dither for it and they look
> > different, some areas look better before and some better afterwards
> 
> looked at more of the 16 color cases with dither 
> (16 colors as i asumed fewer would magnify any issues )
> file 01, IMHO current looks better than last (variance per axis)
> file 02, IMHO current looks better than last (variance per axis)
> file 03, IMHO VPA looks better but both really are quite off in terms of color,
>          thats not the color of the original image.
> file 04, VPA is not good thats not the correct color
> 
> It seems th last (variance per axis) is more pale and looses color
> 

You're right, the variance per axis change is not always very good, I
might dismissed it entirely.

It also makes me question the use of the variance entirely when splitting
the boxes. I need to investigate if choosing the box with a simpler
heuristic (something naive like picking the box with the highest volume)
is not actually improving things.

I'll investigate and share the results.

Thanks for looking deeply into that!

> > Have you done any double blind comparission ?

Nope, I probably should, but I'm not sure I have the energy to setup such
a thing yet.

Regards,

-- 
Clément B.