Mental Ray | Illustration | Ambiant Occlusion VS Global Illum.

Lately I had the opportunity to test Mental Ray. In MR 3.4 I found “Ambiant Occlusion”, a shading tool that is becoming a true alternative to Global Illumination. Amb. Occ. is nothing new to CG, but it last implementation in Mental Ray comes with a lot of handy parameters :

  • sampling rate : quite obvious, will determine the amount of rays cast by the shader
  • spread angle : will make the probing from narrow to wide angle, thus more or less sensitive to the details around
  • distance : a critical parameter that define the probing range from near to far

Among them, Distance is a real breakthru against Global Illumination. Small probing distance make shorter render times (more than 200% in some cases). And it gives subtles areas of shadow.

Of course, it doesn’t take account of the “boucing energy” phenomenon. Fortunately that’s the funniest part of the lighting job : adding pointlights here & there to mimic the bouncing of light. That what I did in this scene.

In the end, hires render time came under 2 minutes (VS 8 minutes for a full GI solution with LW)