Merge "mask/stencil" and edge issue

[Simma]

Hi all,

I've noticed something that I haven't noticed before. See attached script. Basically, if I connect both input of a merge node to a premultiplied alpha, I loose some edge details. I noticed the same thing by for example adding a multiply node, connect both the input and mask input to the alpha and bring it all down. I loose edge details. I would expect nothing would change, but I'm guessing it's some kind of premultiply issue? How would you tackle this?

Thanks for your help.

[radders]

Yeah, you are effectively double premultiplying. If you have a pixel that is already 0.5 and you apple the same alpha to it again you are doing 0.5 x 0.5 = 0.25. This is what I would expect to happen. You shouldn't need to mask something that is premultiplied by itself.

One thing I did discover about mask/stencil the other day is that if clamps the RGB values to 1. I had to use multiply instead to keep my float values intact.

[Simma]

Thanks for your reply radders, makes sense.