black outline on alpha

[stevesideas]

I'm not sure what I am doing wrong. Normally I can render out an object to be comped without any outline but with this scene I cannot. I have a helicopter rendered on a black background. The lighting etc is all in the env override.

I'm using motion blur on just the blades. There is a dark outline around the body of the heli - as shown below



The background is totally black. I am saving out to EXR with alpha.

[Morne]

did you also add the lighting in the reflection/refraction env override?

[stevesideas]

Yep. All 3 have the same vray sun map.

[Morne]

Is this for a still or animation? Are you comping with PhotoChop or Nuke?

Maybe pre-multiplied issue?

[stevesideas]

I'm comping with aftereffects. It's an animation. I've done this method before and not had this problem so it's confusing me completely ! I thought you only had to render to a black background with the lighting in the env slots as we've discussed and then output to an 32bit EXR with alpha. I was using straight comp method in aftereffects but it lost detail in the motion blur parts of the helicopter rotors. If I premult the image I have to make the matt colour a light gray to reduce the edging but I'm pretty sure this isn't a correct comp with perfect alpha.

[Morbid Angel]

it happens when you multiply elements over each other, you need to unpremultiply everything by the alpha, do your comp then premultiply it again.