Vray Diffuse Filter

V-Ray V-Ray Common Public
1

Hello all,

I have come across a problem when rendering out in passes.
I turn on Vray DiffuseFilter and when it renders out I get this:

You can see that it is not rendering correctly since there is some sort of shading in there. It is not caused by any lights since this is how the final render turns out.

I have narrowed down the problem to happen when I use a falloff map or turn on Fresnel reflections. When neither of those are on, the diffuse renders correctly.

Any ideas on how to get around this?

Thank you,
Keith

2

what version of vray? And could you share the problem scene?

3

Version 1.5
http://keithbeltramini.com/passes.zip

Thanks!

4

I can confirm this problem. The diffuse element isn’t completely disregarding reflections when rendered. In fact if you turn off fresnel, and have a complete mirror surface, you lose all diffuse, which technically is correct, but not in the spirit of what a diffuse element is used for.

5

I feel it is rendering correctly. If you think about how a fresnel falloff works then as you look at a surface at a shallower angle i.e. as the surface is further away then you will see more of the reflection and less of the diffuse colour. That is why it appears to darken here, so that when you place the reflection pass over it with an additive blend mode it retains the correct illumination value. If the diffuse remained the same value all over then the areas with higher reflections would come out too bright when composited with the reflection pass.

6

You might be correct, but I feel its a difference in philosophy. The vrayReflectionFilter is there to give you the proper fresnel value.

7

I guess I feel that certain render elements, diffuse being one of them, should be created completely independent of other passes.

8

I’m afraid I don’t know enough about the ins and outs of the render elements to say for sure, I was more commenting from a theoretical point of view. I’m sure one of the developers could clear it up properly though.

9

Sure. But even on a theoretical level, I would think a compositor would want the diffuse pass to be without shading, and then the reflection pass would incorporate the necessary adjustments to lay over the top of the diffuse pass correctly.

10

I completely agree. If it is something that is happening due to changes in the reflection, why would it alter the diffuse map?

Odd.

11

What did you mean by ‘in the spirit of what a diffuse element is used for’? Surely what it is used for is to composite with other elements to give a complete image. In the case of a mirror surface as you said there is no diffuse, just black. When this is overlaid with the reflection pass in additive mode then it gives the correct result. What other colour should a mirror surface be in the diffuse element but black? By that rationale then a surface with a fresnel reflection should surely be a gradient going from full diffuse at 90° to pure black when viewed at 180° to the surface. Would you not agree?

Edit: Sorry not fully black, but a darker value depending on the IOR.

12

Well both scanline and mentalray do it like vray does, so I suppose your right.