[Bf-committers] Dithering

[Goran Kocov]

--- Alexander Ewering <blender at instinctive.de> wrote:

> 
> On Wed, 27 Oct 2004, Roland Hess wrote:
> 
> >> 
> >> This looks *very* promising, though I'm a bit
> worried about animation
> >> "flickering" if it uses random noise.
> >> 
> >> Ton, you should have a look at this :)
> >> 
> >> | alexander ewering              instinctive
> mediaworks
> >> | ae[@]instinctive[.]de  
> http://www[.]instinctive[.]de
> >
> > In my experience in image manipulation and
> commercial printing, a noise 
> > variance of only1% in the luminosity of an image
> is enough to remove visual 
> > banding. At that level the noise is almost
> unnoticable to the naked eye. I 
> > would be very surprised if it caused flickering in
> an animation. If anything, 
> > it would give it a slightly more organic feel. The
> only problem I would 
> > foresee is that it would screw with frame
> differential compression methods.
> 
> Only if it is purely random. Floyd-Steinberg
> dithering uses a 'fixed'
> kind of 'noise' (it's not even noise), so it should
> also work well with
> those compression methods.

I don't know a lot about dithering algorithms, so I
spent some time this afternoon googling for
Floyd-Steinberg dithering. From what I understood
about it, it's not possible to implement F-S dithering
in Blender without rewriting a big part of the
renderer. At the moment, the float to char conversion
takes place immediately (or almost immediately) after
a pixel has been rendered. In order for the F-S
dithering algorithm to be able to function, at least
two scanlines need to be kept as float before
converting their pixels to char. 

IMO, a sophisticated dithering algorithm may be of big
importance when converting an 8-bit greyscale image to
a 1-bit black-and-white one, but when converting from
a floating point to an 8-bit image, a simple random
dithering algorithm can do the job just fine (not
counting the compression problems). 

Goran



		
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