by Kali » Sun Jun 19, 2011 8:50 am
* Make sure the background colour is the same as the background on the model.
* When you make the selection to take to the alpha channel, make sure it's antialiased and then expand it by one pixel
* Only then fill the alpha channel in.
That way your jagged edges will be in the background colour, hopefully, which shouldn't show up. I say shouldn't because there's other issues like specularity which will change the background colour, but it should be nearer.