Hi all
Whats the difference between sticking a VRayHDRI into the Environment override slot and sticking it into a VRayLight? Which one is the preffered method?
VrayHDRI light is faster and has better sampling. It smooths out the HDR based on a SIGGRAPH paper that was released several years ago. It also gives you more control.
thanks for the reply but I’m unclear of what you mean. Do I stick the VrayHDRI into a VRaylight or into Env override? I’m thinking you mean stick it into a VRaylight?
Here’s some tests I did a couple of years ago when I was trying to figure out the same thing. For HDRIs with a relatively low dynamic range I tend to use the environment option as the dome light seems to require better sampling to reduce noise. However if you’re using HDRIs with a very big dynamic range then the environment option can become very unpredictable and introduces a lot of artifacts while the dome light will give you nice crisp shadows.
Hope that helps!
This is correct with the exception that is is not based on any SIGGRAPH paper specifically 
Best regards,
Vlado
Oh. I thought it was somewhat related to the Median Cut Algorithmn:
http://gl.ict.usc.edu/Research/MedianCut/
Anyways…
While a bitmap in the BG slot gets sampled by GI rays uniformly, potentially wasting sampling for low-contrast, low-contribution areas, and so forcing the user to crank up the number of rays shot, the DomeLight pre-processes the image, finding the most important areas (read: sun, light-sources, generally the brightest, most light-contributing areas of the image), and concentrating the sampling there.
So, for the same number of rays shot, the importance-sampled domelight works much better (cleanly) than a GI with a BG image.
One of the things we have been doing when using Hdri images is to use a blurred downsized hdri for diffuse lighting a higher res map for reflection and a high res jpg for background.
When using the dome light how does the resolution option work?
If I have a 2k image and set the dome to 512 resolution is that 512 resolution just for the pre-process before it importance samples and then it uses the 2k image for both diffuse light and reflections?
If your image is 2k and the dome light resolution is 512, then the dome light will downsample the image for importance sampling. For reflections, the full 2k image will be used.
Best regards,
Vlado