- Posts: 266
- Joined: Sun Jul 15, 2018 1:50 am
- Real Name: Paul Rayner
Put an Alpha Divide right before the grain node and an Alpha Multiply right after. The grain will get applied to the entire image, but then multiplying by the alpha will knock it back down to 0 in the transparent areas. Dividing out the alpha first ensures you don't get a double-premultiplication.
However, if there are portions of the image that have non-zero RGB with zero alpha, this will destroy those pixels. If that's the case, then you'll need a different method. I'd have to give it a big think to figure out what that method might be, though.