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ACM SIGGRAPH Asia 2018 (Transactions on Graphics)

Practical Multiple Scattering for Rough Surfaces
  Joo Hoo Lee Adrian Jarabo* Daniel S. Jeon Diego Gutierrez* Min H. Kim  
  KAIST *Universidad de Zaragoza, I3A  
  Three different objects made of rough conductors (gold, silver, and copper), with spatially-varying roughness specified by a texture, rendered with the Cook-Torrance model (left) and our multiple-scattering-aware microfacet model (middle). Cook-Torrance assumes single scattering, which results in significant energy losses, specially for rough surfaces, as shown in the difference image (right). Our model accounts for multiple scattering in a closed-form analytical way, therefore conserving energy, with a small overhead, and without the need for costly stochastic light transport simulations.  
  Microfacet theory concisely models light transport over rough surfaces. Specular reflection is the result of single mirror reflections on each facet, while exact computation of multiple scattering is either neglected, or modeled using costly importance sampling techniques. Practical but accurate simulation of multiple scattering in microfacet theory thus remains an open challenge. In this work, we revisit the traditional V-groove cavity model and derive an analytical, cost-effective solution for multiple scattering in rough surfaces. Our kaleidoscopic model is made up of both real and virtual Vgrooves, and allows us to calculate higher-order scattering in the microfacets in an analytical fashion.We then extend our model to include nonsymmetric grooves, allowing for additional degrees of freedom on the surface geometry, improving multiple reflections at grazing angles with backward compatibility to traditional normal distribution functions. We validate the accuracy of our model against ground-truth Monte Carlo simulations, and demonstrate its flexibility on anisotropic and textured materials. Our model is analytical, does not introduce significant cost and variance, can be seamless integrated in any rendering engine, preserves reciprocity and energy conservation, and is suitable for bidirectional methods.
  author  = {Joo Ho Lee and Adrian Jarabo and Daniel S. Jeon
             and Diego Gutierrez and Min H. Kim},
  title   = {Practical Multiple Scattering for Rough Surfaces},
  journal = {ACM Transactions on Graphics (Proc. SIGGRAPH Asia 2018)},
  year    = {2018},
  volume  = {37},
  number  = {6},
  pages   = {275:1--12},
  doi     = "10.1145/3272127.3275016",
  url     = "",
Preprint paper:
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Supplemental document:
PDF (10.1MB)

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