Prepasses for Irradiance Maps

[mjm223]

I've noticed on occasion when I'm rendering an image on VRay that the number of prepasses change. I use the Irradiance Map as my primary engine and the Light Cache as my secondary. I don't really change any of the settings when I render different images (except for the output size).

Most of the time, an image has 4 prepasses, but sometimes it'll have either 2 or 1. Does VRay automatically determine the number of prepasses needed to render the image, or is there a setting in the VRay Options that will allow me to adjust the number of prepasses?

[dalomar_cg]

Re: Prepasses for Irradiance Maps

Prepasses tell you NOTHING...5 prepasses doesn't mean good or bad...2 prepasses doesn't mean much either. What determines the number of prepasses is the numeric "distance" between your minimum and maximum rate*. So -3,-1 yields 3 prepasses...-8,-6 also yields 3 prepasses, but you can expect a significant drop off in quality between the two. In general, its good to have between 3 and 5 prepasses...fewer and you're probably not getting enough adaptation in your solution and too many you're likely to get artifacts.


*There is one current exception to this and one potentially future one. There is an option within IR that is enabled by default called Multipass, which forces each "level" of IR calcs to be done separately. Disabling that will force them all to be done at the same time (same calcs though) and therefore will only result in one prepass. The future exception has to deal with interpolation, but that's another subject.

[mjm223]

Re: Prepasses for Irradiance Maps

Cool, thanks for clearing that up for me, Damien.