[Gllug] Faster maths?

[Richard Jones]

On Thu, Mar 08, 2007 at 11:11:26PM +0000, Adrian McMenamin wrote:
> I have some perl which indexes and dithers a PNG image to a 256 colour
> palette.
> 
> The indexing is pretty fast - a 59K (compressed) PNG image on a 4000
> BogoMIPS machine in about a second.
> 
> But I turn on dithering it takes half an hour!!
> 
> The bottleneck appears to be calculating the distance of a point in
> colourspace (ie the original colour + diffused error) from any point in
> the palette (to find the closest match).
> 
> I don't use sqrt - just compare square with square (and save a match so
> don't have to do the same lookup twice).

There's a fast, high-quality implementation of this algorithm in the
source code to xv.  Unfortunately it has a non-free license ...

Rich.

-- 
Richard Jones
Red Hat
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