Alpha channels and such

Hi Folks - I recently asked a simple question about alpha channel formation in Radiance and got a nice answer from Peter. So, I'm looking around and trying to come up with some nifty ideas for pulling off such a stunt and, as a very new user to Radiance, I find that Radiance has its OWN FUNCTIONAL LANGUAGE. Well, that makes me feel better, because I spent a while figuring out the mechanics of the "if" statement in the man page example for pcomb. Damn if this software isn't just the coolest.