You can choose to render your objects with split-alpha, at least with TGA files. Then you'll have a mask, and an image.
"Don't anti-alias against background" makes jaggies against background though.
Tried rendering against a black background?
"Note: You must be rendering against a black background if Don’t Antialias Against Background is turned on. "
"Don't anti-alias against background" makes jaggies against background though.
Tried rendering against a black background?
"Note: You must be rendering against a black background if Don’t Antialias Against Background is turned on. "