Fwd: Convolution

[Bart Coppens]

On Thursday 26 May 2005 10:50, Boudewijn Rempt wrote:
> The curious thing is, I've tried to use
>
> depth = src -> colorSpace() -> nColorChannels()
> instead of
> depth = src -> colorSpace() -> nChannels()
>
> and the emboss/edge detection filters stopped working correctly, although
> the sharpen and blur filters worked fine. I wonder what I am doing wrong --
> my experiments with convolution have been marred by integer overflow,
> off-by-ones and a complete disregard for correct coordinate calculation so
> it could be anything :-).
Well, maybe that's because I put a -1 there somewhere, to avoid affecting the 
alpha channel with regular filters.

> As for the selection: I guess nothing much changes there. You need just the
> one kernel, and have it operate on all the channels in the paint device,
> i.e, just the alpha channel.
Yes, but I feared this would give very strange effects if you tried to apply 
something like edge detection on the alpha channel. It could work, though, I 
never actually tried it :)