Nuke and reflection pass.

[nomads]

Hi,


I am having lots of problems with compositing the reflection pass.

I get fringing around the edge of my objects.

I have tried using both methods Vray reflection pass and Vray raw reflection and still get fringing.

I am using the reflection pass as a plus.

Am I doing something wrong or can you only go so far with compositing.

thanks

[cheerioboy]

are you doing an unpremult + premult?

I think you need to unpremult(iply) each pass, combine, and then premult(iply)..
Maybe share a screen grab of your comp, or attach some basic files of your issue to troubleshoot.

- a dirty solution is to take that reflection pass and do an errode on the alpha to eat off that fringe.

[nomads]

I think your right.


I can sort of make it work by grading the back plate to black and adding it on top.

[Morbid Angel]

You need to render your main object against black, in case your background is not black this will also contribute to the problem. As cheerioboy pointed out though you need to first unpremult everything then do your layering, then primult it again by the alpha at the end of the comp.

[nomads]

I am trying to color correct an object using MultiMatteElements.

The grade is creating halos. Unpremultiplying grading and premultiply makes worse artifacts.

Is there a procedure for grading with MultimatteElaments that does not cause this?

[nomads]

Does that mean breaking up the objects in the scene into elements and rendering them each separately against back?

[Morbid Angel]

Does that mean breaking up the objects in the scene into elements and rendering them each separately against back?

yeah that's probably your best bet.

[nomads]

Is there an easy way of doing this?

Im thinking it would be quicker to render it properly in max and not bother with compositing.

[nomads]

Is there some sort of way of using render elements to render the object id's onto black in the diffuse?

[Svetlozar Draganov]

I am trying to color correct an object using MultiMatteElements.
The grade is creating halos. Unpremultiplying grading and premultiply makes worse artifacts.
Is there a procedure for grading with MultimatteElaments that does not cause this?

Can you send us a sample Max/Maya scene files along its nuke-composition and render elements for investigation?
Have you tried to work with deep-exr files? They usually provide a more elegant and easy solutions to these hallo-issues.

[nomads]

Hi

I have put up a we transfer link. It includes .max .nk and a renderd still. http://we.tl/zIW1MEZN4J



In nuke when I adjust the diffuse with multimatElement2.red I am getting white outlines.

The yellow objects have the same material. I was concerned there might be a highlight on the curved object. The box has no highlight.


I set up a switch to test deferment methods.

0 is as is

1 is a grade on the diffuse.

2 Is blacking out multimatElement2.red selection and adding the grade on top.

3 is Using premult unpremult.




Version 2 works best


Should I be getting something else out of max? Is there another way to do this.


Thanks.

[cheerioboy]

It looks like if you only want to have a single rendered image, you need to be more gentle with the grading. If you want to push the grade that far, you should look at separating your objects into different renders, background & object, with the object rendered on a black background/alpha. You're getting issues because either way you do it with the single render, using a multimatte mask, or using premult & unpremult, your object's edge is blending with a lighter colored background. So those pixels on the edge will go brighter when you raise the gain or multiply up.

I'm not sure if Deep EXR resolves this? Will need to do some more tests when I'm at the office.
Check this out, http://jokermartini.com/deep-compositing-101/

[nomads]

Is there a way to do this using Render elements?

I have been experimenting with the VRayMtlSelect but haven't got it to work.

[Deflaminis]

Couldn't you just grade the alpha?