alpha channel with a softened matte

[Diego A Grimaldi]

Hey Everybody,

I looked all over this and the Sidefx forum for the answer to my (presumably simple) problem but I couldn't find it.

I am still very new to shops so here is my problem.

I am trying to have an object with an alpha channel with a softened matte.

I am convinced this is a very easy problem, but I really donno how to do it.

Please help!

Thanks

Attached is a picture of my problem and the desired effect.

[Aeonx21]

This is just a hunch but try to render out each of them separately and then take the alpha of the sphere and blur it then apply it to the alpha of the smoke

[Diego A Grimaldi]

Thanks for the reply! In the example I provided that would definitely be an easy solution, but in our actual shot it is necessary to accomplish this in render. We have a body of smoke being composited onto an object and parts of the simulation need to exist in front of the object but other parts need to be occluded (behind the object) at the same time. Any ideas?

[rayman]

It is possible to do this in sops.

Create Sdf represantation of the sphere (using iso offset SOP node).

Then Add Volumevop with ramp or volumeblur node to control edge falloff.

Use Volume Mix and multiply both volumes.

SOP_volumeMix.hip

Edited September 27, 2013 by rayman

[Diego A Grimaldi]

Thanks a lot! I replaced the box in your scene with our pyro simulation and it worked as expected, but when I replaced the sphere with a more complicated mesh (a hand) I had difficulty getting the volume visualization to make a clear cut out of the hand. Played around with the volumevop and volume visualization but no luck. Any tips?