[cairo] Reducing number of colors

[Bernhard R. Fischer]

On Tuesday 02 July 2013 14:33:02 Chris Wilson wrote:
> On Tue, Jul 02, 2013 at 02:04:11PM +0200, Bernhard R. Fischer wrote:
> > On Tuesday 02 July 2013 13:27:00 Chris Wilson wrote:
> > > On Tue, Jun 25, 2013 at 08:16:22AM +0200, Bernhard R. Fischer wrote:
> > > > Hi!
> > > > 
> > > > Image surfaces are supported as true color (24/32 bit) or 5/6/5 bit
> > > > pixels.
> > > > 
> > > > Is there any native way in cairo to reduce colors to fixed number
> > > > palette image?
> > > 
> > > No, there is nothing inside cairo to perform the quantization you wish
> > > - it is outside of Cairo's scope.  I would suggest you hook the output
> > > of your rendering into ImageMagick and use some of its routines to
> > > control the quantization of the image to a fixed palette.
> > > -Chris
> > 
> > Hi Chris,
> > 
> > I think that there is some code somwhere which could be used for that
> > purpose because it is possible to copy a 24 bit surface to a 16 bit
> > surface which obviously requires color reduction.
> 
> The code you mention is src/cairo-xlib-surface.c when pushing images to
> X.  If both are truecolor, we use pixman to do the conversion (or failing
> that do the shifts ourselves). For other formats, we have a relatively
> simple mapping from r8g8b8 to the Visual's palette. That is a much
> simpler task than picking an optimal palette for an image.
> -Chris


Ok thanks. I'll have a look there.

Bernhard
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