Need tips for rendering heavy refractive scene

#1

Hello, im workin on a scene that involves only refractive materials in maya2012 with vray2.0, something that will look as crystals and I cant find any workflow to get decent render times. The scene have simple boxes geometry that forms a coridor and the camera fly close to one of this walls. The renderings without refraction are quite easy around 1-2 mins with lighting but when i activate refraction is imposible to work or even see one frame. i get 3 hours for 960x540 resolution and i have to render full HD in the end.

Right now im using only and hdr for reflections and refractions and one vray mat with colored fog and a bump map. no lights, no gi and still no good render times

So, my question to you guys, are there any tips and tricks, any good renders out there, any special workflows for rendering heavy glass scenes?

Thanks a lot

#2

Things that could work (or not by depending on your renderer) are:

-separate reflections from refraction calculations - depending on your renderer you might need to render both aspects in separate passes and then compose them back in additive mode.

  • no process radiosity reflectivity or inter-reflections for transparent objects.
  • for background transparent objects, make an HDR environment map and use it as spherical map for refractions (and probably reflections).
  • for middle-ground transparent objects, separate them with different material/surface and limit the ray recursion per surface to minimum possible.
  • Limit ray bounces per surface (less for background objects, more for foreground objects).
  • if blurred refractions are needed, limit the sampled ray per surface for middle-ground transparent objects; and for background objects, blur the transparency as pre-processing (by front-projecting blurred background image and displacing this map with an incidence gradient/ramp) or as post-processing with the refraction buffer.
    -if render engine supports sub-frame motion blur, changing IOR in the course of one frame to the other repeatedly, may produce also quicker soft-refractions.

Gerardo

#3

thx a lot gerardo, ill try a couple of them, hope it will speed things up.