Mia_x Passes Plus Nuke Equals Fringe

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  01 January 2014
Mia_x Passes Plus Nuke Equals Fringe

Hey guys,
I hope u can help me with the following scenario, because this gives me bad headaches.

What I want to do:

Compose MIA_material_x passes (from Maya 2013, rendered with MentalRay) in Nuke like this:
Beauty = diffuse_level * (diffuse_raw + (indirect_raw * ao_raw))
+ spec_level * spec_raw
+ refl_level * refl_raw
+ refr_level * refr_raw
+ tran_level * tran_raw
+ add_result

Mia_material_x outputs to writeToColorBuffer outputs to Custom Color pass outputs to OpenEXR 32-bit.

The difference between the compsite and the master beauty is a little fringe around objects with contrasty colors. The fringe occurs when multiplying the diffuse_level pass.
Ive attached 2 images to visualize the problem.

There is a way to composite like this: Beauty = diffuse_result + indirect_result + spec_result + refl_result + refr_result + tran_result + add_result

It works like a charm. I guess because of the plus only commands. But I would like to have more control over indirect lighting, which consists of indirect_raw * ao_raw, what requires the first way.

I really hope u guys can help me.

Regards, Rob.

Fringe (left: beautypass, right: composite)
Nuke Node Graph
Attached Images
File Type: png fringe.png (10.2 KB, 5 views)
File Type: png nodegrpah.png (23.1 KB, 3 views)

Last edited by Yoolan : 01 January 2014 at 05:00 PM.
  01 January 2014
Well I solved the problem.
Maybe out there are people, who are stuggling with the exact problem. For those, read on.

The deal is that you cant use the multiply operation in post, because every single render pass is filtered. If you do uncheck the filtering in render passess then everything is fine and there are no artifacts. But who wants non anti-aliased images?
What you can do to minimize this artifacts is using contribution maps to sepreate each object with its own alpha channel and uncheck premultipy in render section. Later on in post you have to premultipy every object with its alpha channel and everything is fine.
But in my case I cant use contribution maps because my scene contains many many objects.
So my little workaround is a little bit weired, but its working.

I wrote that the beauty pass is created by:

Beauty = diffuse_result + indirect_result + spec_result + ...

Beauty = diffuse_level * (diffuse_raw + (indirect_raw * ao_raw))
+ spec_level * spec_ra w+..........

As a consequence:
diffuse_result + indirect_result = diffuse_level * (diffuse_raw + (indirect_raw * ao_raw))
diffuse_result + indirect_result = diffuse_level * diffuse_raw +diffuse_level * indirect_raw * ao_raw

diffuse_result = diffuse_level * diffuse_raw
indirect_result = diffuse_level * indirect_raw * ao_raw

So if you want to have more control over the ao_raw you just adjust the equation:
ao_raw = indirect_result /diffuse_level / indirect_raw.

Therefore you have to render the three passes indirect_result, diffuse_level, indirect_raw and divide them in post to get the ao_raw pass. Now you are to able to adjust the ao_raw pass. And it pretty looks like the one, which is rendered as a custom pass in maya. The only difference are the edges

Okay Im done now. Maybe it will help someone.
  01 January 2014
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