Compositing vray fog

[thanulee]

Hi, whats the proper way of setting up/compositing fog if i wanna do 2 renders, 1 with no fog and another one only with fog element, that would produce a similar result as if i was having everything in 1 scene? Hope i described this proper.

Thanks

[Deflaminis]

32-bit linear add I would imagine...

[thanulee]

Yes, but how? Black objects diffuse? Only diffuse? No gi? How would the second pass be? thanks!

[m_hinks]

Black material in override, turn off GI and maps. Make it render as quick as possible. Add the VrayEnvFog environment effect and select which lights to use. And set up a gizmo works well to control the location of the fog. Should render black and white, and pretty quick. Just doing it on a project now!

[thanulee]

Thanks. And i want scatter gi i should use a fog emmision? This was the first method that i tried and didnt work well in interiors that im doing atm.

[m_hinks]

I find in a lot of cases scatter is not needed, for clouds maybe, but arch viz not so much. If you increase the scatter times from 1 I believe you will also need GI turned back on.

[thanulee]

Yep, and i wanna avoid having GI, so i changed the emission color to fake the gi bounces. I wouldnt go into all this trouble, but its a 3 minute video with some interiors and tight deadline so...
Thanks a lot for the help!