Black Halo After Precomping 3D Render Passes

[Ben Waflik]

Here they are. But note that I don’t have problems when using just one pass. It looks as it should either on a transparent or opaque background, I can even safely precomp it and nothing bad happens. The halo only appears when I’m stacking 2 or more layers on top of each other. I’ve also attached the project file

Main Comp: Opaque BG
Main Comp: Transparent BG
Main Comp: PreComped Passes, Opaque BG
Main Comp: PreComped Passes, Transparent BG
PreComp: Opaque BG
PreComp: Transparent BG

[Darby Edelen]

This takes some knowledge of the order of operations (specifically blending) in AE.

In the pre-comp you are ‘Add’-ing the reflection and lighting passes to the global illumination pass, but then in the Main Comp all of that information is being blended ‘Normal’-ly with the shadow and background passes. The alphas of the 3 passes in the pre-comp are being added together before the normal blend in the main comp. In addition the color values at the edges actually end up being darker than you’d expect because in the area where the alpha blending occurs in the main comp the additive passes are not added to the background, but rather blended normally. This is simply due to AE’s rendering.

There are 2 solutions for this problem.

The first is easy and more accurate, simply enable Continuously Rasterize/Collapse Transformations on the pre-comp layer in the main comp, however this will break if you apply any effects to the pre-comp layer.

The second takes a few steps and results in a slightly less pristine edge:

1. Enable the Layer > Preserve Transparency switch on the 2 additive layers inside the pre-comp. This will eliminate the additive build up of the alpha on the edges and should improve your results some.

2. To deal with the darkening of the color values you can apply the Channel > Remove Color Matting effect to the pre-comp layer in the main comp. This will result in some overbright values at the very fringes of the layer so apply the Channel > Set Matte effect to matte those out.

I’ll also add that I don’t usually run into the issue you’re having here when using Unmult through the EXtractoR effect so I have a suspicion that there may be better render settings for AE in your 3D package that won’t require the above workarounds.

Darby Edelen

[Ben Waflik]

This is simply due to AE’s rendering

Thanks for explaining how Ae renders things, just what I wanted to know!

…simply enable Continuously Rasterize/Collapse Transformations on the pre-comp layer in the main comp…

Yeah, I need to add effects to the precomp so it won’t work.

…apply the Channel > Set Matte effect to matte those out

Well, I could apply a “set matte” effect to my precomp, but then, if I’ll add a glow, say, to the reflection pass, it won’t go beyond the matte I’ve set.

I’ll also add that I don’t usually run into the issue you’re having here when using Unmult through the EXtractoR effect…

But how? I made a test even with plain red and blue solids using “add” blending mode. I applied feathered circular masks to them, precomped and got halo too!