Right I've got the shrinking the rendered image to create colour map + alpha channel working.

The top two quadrants are renders the bottom two are the generated colour and alphamaps (scaled up).
Now I need to squirt the data into a sprite to see if it works properly.
The top two quadrants are renders the bottom two are the generated colour and alphamaps (scaled up).
Now I need to squirt the data into a sprite to see if it works properly.