Note: I am posting this in the maya section, but the potential workaround I have found is only available in 3dsmax (skylight portal for VrayDomeLight). All the image below were rendered using 3dsmax.
It would seem I cannot get the correct result in my Global Illumination render element when using the VrayDomeLight. There seems to be additional light information included in the global illumination that, correct me if I’m wrong, is incorrect. It is affecting both the Global Illumination render element and the final ‘Beauty’ frame.
I have found a potential workaround, enabling ‘Skylight portal’ for the domelight, however this option is not currently available in maya (only 3dsmax), and we need to find a solution in maya.
Please find some images attached below that illustrate what I’m talking about, all renders using the same VrayDomeLight with a generic HDRI, only setting that was changed was use 'Skylight Portal.
Beauty - Skylight Portal = Off
Beauty - Skylight Portal = On
GI - Skylight Portal = Off
GI - Skylight Portal = On
GI - Difference between - Skylight Portal = On + Skylight Portal = Off
Things seem to work as expected. V-Ray uses multiple importance sampling to calculate the contribution of the dome light, which means that it will be present both in the GI and in the direct lighting channels. When you add both together you get the actual contribution. Not doing MIS usually results in increased noise and longer render times.
Doing some tests rendering 2 images, one with GI, and one without, extracting the difference between the VrayLighting element from both passes, then removing it the difference from the GI element gives me the seperate control over the GI. However, as you said, it is resulting in ‘increased noise and longer render times’, especially given I need to do 2 separate renders. The interesting thing is, I get a much cleaner, similar result using the ‘skylight portal’ cheat, with all the control I need. Is there any chance the ‘skylight portal’ option could be added to the VrayDomeLight in maya?
