alpha channel?

can anybody tell me where can I find good tutorial about alpha channel and how it works?

you could try;
http://www.keithp.com/~keithp/porterduff/p253-porter.pdf

cheers,
John

thank for your help

This site

nehe.gamedev.net

Originally posted by alpha1:
can anybody tell me where can I find good tutorial about alpha channel and how it works?