Am 17.04.2012 19:54, schrieb zzzzzz:

> What should be the best way to achieve this ?
> The Dreambox expects an 8-bit paletted PNG file

Are you sure 24 bit PNG with 8 bit alpha channel doesn't cut it?

> Right now I create the image in TGA format in Povray with the +ua option, so
> that the background is transparent.
> Then I use Imagemagick to convert this image to GIF, thereby automatically
> converting the 24 bit colour with 8 bit alpha channel to a 256 colour palette
> file, then convert it with the same tool to PNG.
> The result is far from perfect, though.

Of course - GIF supports only one single transparent palette entry. As 
far as I know, PNG does support semi-transparent palette entries.

> As you can see from the edges, the edges are rough because of this double
> transformation.

Can't you convert from TGA to 8-bit paletted PNG directly? I'd expect 
Imagemagick to be able to do that stunt.

> I was wondering if there was a way to immediately create such an 8-bit paletted
> PNG file from within Povray itself, or if there is another, better way to obtain
> this result.
> Does anyone know a way of doing this ?

POV-Ray does not support paletted image output in any format; the reason 
is that there are plenty of different ways of choosing a suitable 
palette, and plenty of different ways to dither the image, each with 
their own strength and weaknesses, so we leave that job up to image 
processing software as a post-processing step.

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