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Rich-VPLs for Improving the Versatility of Many-Light Methods

Florian Simon, Johannes Hanika, and Carsten Dachsbacher

Computer Graphics Forum (Proceedings of Eurographics 2015)

Rich-VPL
The Disco-scene with multiple colored light sources and reflected highly-glossy caustics where colors add to whitish light. Rendered with our new virtual light type “Rich-VPL” (left), standard VPLs (middle left), virtual spherical lights (VSL, middle right), and path tracing reference (right). All many-light methods use 25k virtual lights; our method introduces an overhead of about 50% (less in more complex scenes) on top of standard VPL rendering, but significantly improves the ability to capture glossy and near-specular light transport. VSL require about 20% additional rendering time on top of standard VPLs due to stochastic sampling.
Abstract
Many-light methods approximate the light transport in a scene by computing the direct illumination from many virtual point light sources (VPLs), and render low-noise images covering a wide range of performance and quality goals. However, they are very inefficient at representing glossy light transport. This is because a VPL on a glossy surface illuminates a small fraction of the scene only, and a tremendous number of VPLs might be necessary to render acceptable images. In this paper, we introduce Rich-VPLs which, in contrast to standard VPLs, represent a multitude of light paths and thus have a more widespread emission profile on glossy surfaces and in scenes with multiple primary light sources. By this, a single Rich-VPL contributes to larger portions of a scene with negligible additional shading cost. Our second contribution is a placement strategy for (Rich-)VPLs proportional to sensor importance times radiance. Although both Rich-VPLs and improved placement can be used individually, they complement each other ideally and share interim computation. Furthermore, both complement existing many-light methods, e.g. Lightcuts or the Virtual Spherical Lights method, and can improve their efficiency as well as their application for scenes with glossy materials and many primary light sources.
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Bibtex
@article{2015_rvpl,
  title = {Rich-VPLs for Improving the Versatility of Many-Light Methods},
  author = {Florian Simon and Johannes Hanika and Carsten Dachsbacher},
  year = 2015,
  volume = 34,
  number = 2,
  journal = {Computer Graphics Forum (Proceedings of Eurographics)},
  month = {May},
  pages = {575--584}
}