Opacity map performance tweak in VRay

I recently did some test to confirm that disabling the map filtering op an Opacity map in a VRay material improves performance. This is a well know trick that can save you some time if your scene contain a lot of these kind of maps. All following tests are done with the universal settings described in the help files, VRaySun & Sky.

The first test is done without any tweak, simple metal louvres with small circular holes :

Rendertime is 2m53s

Then when tweaking these vaules in the Opacity map parameters :

And then after a rerender :

note how the rendertime has dropped : 2m13s… almost 30% faster ! The only bad side is that the overlapping shadows are less transparent… but in many cases it won’t be a problem.

Then I had the idea to test the workaround we did used in the good old days, when the VRay materials hadn’t an opacity slot ;) The trick was simple, the “opacity” bitmap in the refraction slot and an IOR of 1.0 to avoid refraction.

The result is intresting : 2m38s and no real difference. Faster than the simple opacity slot but slower than the unfiltered one. But there are disadvantages : You can’t use refraction slot anymore, you have to mask every other texture to avoid, for example, reflection in the holes, and the object will appear without his holes in some render pass like VRayWireColor (whereas the opactiy slot won’t have this problem)

I’ll conduct other test shortly to see if there are special cases where the refraction technique would be faster than the opacity one, but I doubt it will happen.