VrayEnvironmentFog and split render passes

[AbeMata]

Hello. Is it possible to have vray environment fog affect your scene ie scattering gi and obscuring lighting, but be non visible to the render?

I like the way the fog affects the overall look, but want to split the passes for comp.


I'll answer this and just say "no", but maybe you guys have an idea What I should do is light my beauty to simulate fog scattered gi and render a separate atmosphere
pass without scatter gi.

Ideas? Thanks guys.

[Svetlozar Draganov]

There is an option Affect Camera Rays under the Ray Filter rollout which will make the fog invisible in the render while GI scattering, Light obscuring and all other fog-features will be still taken into account:

[AbeMata]

Wow, thanks I guess I've been programmed to look for the phrase "visible to camera"

[AbeMata]

Attempting to comp them together. First image is the fog rendered with the environment. Second is
the comp assembled. Noticing some differences. Some fog is missing and the lighting looks different.
Its just a normal slap in after effects. No blending modes just a over b.

[Svetlozar Draganov]

The difference most likely comes from the fact that the GI-scattering on the Environment Fog is missing.
When Fog is invisible and GI-scattering is activated V-Ray will calculate GI scattering contribution from the Fog over the objects in the scene, the GI scattering on the FOG itself won't be rendered.
This information is also missing in the Atmosphere pass since GI scattering is disabled.

[AbeMata]

To get this straight, gi scattering will affect only what is visible to the camera? Invisible fog will gi scatter for the visible environment, but not itself. Does that mean when the fog pass is rendered alone, the gi contribution from the invisible environment onto the fog is not calculated?

I have the scatter gi checkbox checked for both passes, of course.

edit: This cant be, as I can generate more gi from the matted environment onto the fog pass. Perhaps I'm misunderstanding the issue.

[Svetlozar Draganov]

To get this straight, gi scattering will affect only what is visible to the camera? Invisible fog will gi scatter for the visible environment, but not itself. Does that mean when the fog pass is rendered alone, the gi contribution from the invisible environment onto the fog is not calculated?
I have the scatter gi checkbox checked for both passes, of course.
edit: This cant be, as I can generate more gi from the matted environment onto the fog pass. Perhaps I'm misunderstanding the issue.

If Scatter GI was enabled for both passes the GI both Fog and Visible Environment is properly calculated.
I assumed that the Environment Fog pass was calculated with Scatter GI off since in your first post in this thread you've mentioned that you would like to turn it off for the Environment Fog pass.

The discrepancies between the composition and the beauty pass might also comes from the way that both passes blends together.
In order to get perfect result you should also consider the depth information. Blending both passes without considering the depth will not give the proper final look since the Fog affects distant objects more than ones close to the camera. The Depth information might be extracted via VRayZDepth render element - use this element as a blending mask when merging both passes.