Simple and robust iterative importance sampling of virtual point lights

Iliyan Georgiev, Philipp Slusallek
EUROGRAPHICS 2010 (short paper)

By probabilistically rejecting virtual point lights (VPL) with low estimated image contribution, our algorithm concentrates more VPLs in areas that are relevant to the current view point. For the indirectly lit EG scene on the left, with light coming from around the corner behind the camera, only 7% of the proposed VPLs are accepted for final rendering. The resulting efficiency increase of more than an order of magnitude allows us to achieve much higher quality with the same number of VPLs. For the Sponza and Living room scenes on the right, the acceptance rates are 28% and 23% respectively.


We present a simple and practical algorithm for importance sampling virtual point lights (VPLs), suitable for multi-pass rendering. During VPL distribution, a Russian roulette decision accepts each VPL proportionally to its estimated contribution to the final image. As a result, more VPLs are concentrated in areas that illuminate the visible parts of the scene, at the cost of a negligible performance overhead in the preprocessing phase. As VPLs are sampled independently and proportionally to their camera importance, the algorithm is trivial to parallelize and remains efficient for low sampling rates. We show that this sampling scheme is well suited to both well illuminated scenes as well as for difficult visibility conditions. Moreover, in contrast to bidirectional and Metropolis VPL sampling, the algorithm is fast and very simple to implement, and uses a single Monte Carlo sampler, making it easier to maintain good VPL stratification.

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BibTeX reference

  author    = {Iliyan Georgiev and Philipp Slusallek},
  title     = {Simple and Robust Iterative Importance Sampling of Virtual Point Lights},
  booktitle = {Proceedings of Eurographics 2010 (short papers)},
  year      = {2010},
  editor    = {H. P. A. Lensch and S. Seipel},
  title     = {EG 2010 - Short papers},
  pages     = {57-60},
  issn      = {1017-4656},
  address   = {Norrkoping, Sweden},
  publisher = {Eurographics Association}