[Photoshop] Assigning transparency based on color values
I have a 32 bit image I wish to import into photoshop. It's an anti-aliased 2d black circle. Currently it's opaque and sitting on a white background.
The idea is to make the background transparent. Now, I know there are other options. But I'm trying to explore the possibility of setting individual pixels transparency level based on their B value in the HSB color mode or some other more appropriate method that translates the anti-alias rim into several grades of transparent pixels. On this simple case, white would translate to completely transparent and black to completely opaque, with all shades of grey in between gaining their appropriate transparency levels.
Incidentally, this goes hand-in-hand with the possibility of building some sort of filter that I can adjust to other things, like setting transparency levels based on color values...
Being somewhat brain damaged on these matters, can you give me a few pointers on where to start?