[ptx] ALpha blending 24 bit images

[Pablo d'Angelo]

Daniel M. German schrieb:
> Does anybody have a simple (but stable) algorithm to alpha blend two
> 8 bit-per color pixels? Or point me to a place where I can find it?
> I am trying to generate JPEGs with PTmender and this is one of the
> last steps missing.

I don't know how about the blending itself. For seam generation as done by 
nona, I have used the nearest feature transform as implemented in enblend. 
However, this doesn't give you a feathered mask, just the boundary.
But I guess a feather mask could be creating by extending the algorithm, 
since it basically calculates a distance of the seam from the border of the 
overlap. This distance could probably be also reused for calculating the 
alpha values along the seam.

ciao
   Pablo