mental ray Architectural and Design Visualization Shader Library

48 2 Architectural Material2.6 Tips and Tricks2.6.1 Final Gathering PerformanceThe Final Gathering algorithm in mental ray 3.5 is vastly improved from earlier versions,especially in it’s adaptivity. This means one can often use much lower ray counts and muchlower densities than in previous versions of mental ray.Many stills can be rendered with such extreme settings as 50 rays and a density of 0.1 - if thiscauses “over-smoothing” artifacts, one can use the built in AO (see page 29) to solve thoseproblems.When using Final Gathering together with GI (photons), make sure the photon solution isfairly “smooth” by rendering with Final Gathering disabled first. If the photon solutionis noisy, increase the photon search radius until it “calms down”, and then re-enable FinalGathering.2.6.2 Quick Guide to some Common MaterialsHere are some quick rules-of-thumb for creating various materials. They each assume basicdefault settings as a starting point.2.6.2.1 General Rules of Thumb for Glossy Wood, Flooring, etc.This is the kind of “hybrid” materials one run into in many architectural renderings; lacqueredwood, linoleum, etc.For these materials brdf fresnel should be off (i.e. we define a custom BRDF curve). Startout with brdf 0 degree refl of 0.2 and brdf 90 degree refl of 1.0 and apply some suitabletexture map to the diffuse. Set reflectivity around 0.5 to 0.8.How glossy is the material? Is reflections very clear or very blurry? Are they Strong or Weak?• For clear, fairly strong reflections, keep refl gloss at 1.0• For slightly blurry but strong reflections, set a lower refl gloss value. If performancebecomes an issue try using refl interpolate.• For slightly blurry but also very weak reflections one can often “cheat” by setting a lowerrefl gloss value (to get the broader highlights) but set refl samples value to 0. Thisshoots only one mirror ray for reflections - but if they are very weak, one can often notreally tell.• For medium blurry surfaces set an even lower refl gloss and maybe increase therefl samples. Again, for performance try refl interpolate.