[Austin Page]

Using a black background is useless if one is trying to use any of the myriad of effects in Looks to blend a CG element into a background plate for example – such as adding halation to just the rendered elements.

My fairly easy work-around that seems to work ok is the following:
1. Precompose the element(s) you want to apply Looks to that needs to maintain an alpha edge.
2. Inside the precomp add Looks on an adjustment layer above your footage.
3. Then below your footage add a solid that fills the whole background area.
4. Set that solid color to be pure white.
5. Then set the blending mode for the solid to Multiply.
6. In your main comp click the “continuous rasterization” option (looks like a little sun icon) for that pre-comp layer, and that should resolve the issue.

Inside the precomp Looks sees everything as 100% opaque. In the main comp the white background disappears because of the blending mode.

Hope it helps someone.

[Austin Page]

what was the solution?