I'm a little confused about the differences between the two in the render queue. I've used RGB+Alpha before to composite stuff. For some reason I thought I could also export just the Alpha and use that as a trackmat, but when I bring it back in there is no transparency.
The situation is I have a simple animation with a transparent background, which I would like to render and re-import as footage. Of course that gives me a black background and none of the transfer modes are suitable. So I went back and rendered just the alpha channel. Yet when I bring that in and try to merge the two it doesn't work. The problem is the rendered alpha channel doesn't have transparency, it is just black and white.
Like I said this is just me messing around, to fix this I just did a RGB + alpha version, but I was looking for alternatives. Is RGB+A the best/only way to bring in footage to composite? It always creates such a large file so I was looking for other methods.
As opposed to RGB+Alpha, Alpha creates no transparency. It creates a black-and-white image which can be used as a luma matte -- white is completely opaque, black is completely transparent, shades of gray are semi-transparent.
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA