Hi guys! I’m a little confused and am unsure if I’m doing things right with premultiply. Normally when I get a CG render, I just inject into the action node and premultiply inside it and it works (with no black edges). But recently I have come across some instances when I tried to premultiply, white edges appears around the CG layer. Also sometimes if i have to post blur the cg layer, premultiply doesnt work too. So I just use it unpremultiplied and pixelspread to remove the black edges. Not sure if this is the right way. Would love some advice! Thanks!
I always like to do the unpremultiply at the very start using a comp node.
I like to do it this way because the alpha passes through and comes out of the alpha on the comp node 
Unpremultiplying is important if I am doing any grading or mixing up of the AOVs to the CG.
If I need to blur then I multiply back again, blur both RGB and Alpha the same way and then unpremultiply directly afterwards.
Doing it inside action is perfectly fine but I love for it to be explicit in my setups.
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Sometimes errors occur in action when you scale or reposition surfaces that require unpremultiplying.
I believe that the order of events does the resampling before the unpremultiply
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this works awesome! thanks man!
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This bites me allll the time with imported PS layers. So annoying!
The other related thing I just learned - Adobe apparently has a weird way of handling premult in After Effects. I had some premult renders and still go some weird halos.
In After Effects there is a background color which is set on a per-comp basis. Might default to white or black. Apparently when AE premults on export it does some blending with that background color for odd reasons I don’t totally understand, and that can come through.
So on AE comps you definitely want to receive straight alpha renders.
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Or just tell your AE artists to premult only with black like every other app uses and stop being iconoclast nutjobs.
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