Practical Product Path Guiding Using Linearly Transformed Cosines
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Practical Product Path Guiding Using Linearly Transformed Cosines

Computer Graphics Forum (Proceedings of the Eurographics Symposium on Rendering) - 2020
Download the publication : practical_product_path_guiding_authors.pdf [22.1Mo]  
Path tracing is now the standard method used to generate realistic imagery in many domains, e.g., film, special effects, architecture etc. Path guiding has recently emerged as a powerful strategy to counter the notoriously long computation times required to render such images. We present a practical path guiding algorithm that performs product sampling, i.e., samples proportional to the product of the bidirectional scattering distribution function (BSDF) and incoming radiance. We use a spatial-directional subdivision to represent incoming radiance, and introduce the use of Linearly Transformed Cosines (LTCs) to represent the BSDF during path guiding, thus enabling efficient product sampling. Despite the computational efficiency of LTCs, several optimizations are needed to make our method cost effective. In particular, we show how we can use vectorization, precomputation, as well as strategies to optimize multiple importance sampling and Russian roulette to improve performance. We evaluate our method on several scenes, demonstrating consistent improvement in efficiency compared to previous work, especially in scenes with significant glossy inter-reflection.

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See also

More information

Project code, Supplemental material, EGSR 2020 Presentation.

Acknowledgements and Funding

This research was funded by the ERC Advanced Grant FUNGRAPH (No. 788065,, and by software donations from Adobe. The authors are grateful to Inria Sophia Antipolis - Méditerranée "Nef" computation cluster ( Clusters_Home) and National Systems of Compute Canada for providing resources and support. We would also like to thank Thomas Müller and Stephen Hill for publishing their code, Sebastian Herholz for sharing his code and scenes, Sebastien Morgenthaler for help with several scene exports and Benedikt Bitterli for his rendering repository.

BibTex references

  author       = "Diolatzis, Stavros and Gruson, Adrien and Jakob, Wenzel and Nowrouzezahrai, Derek and Drettakis, George",
  title        = "Practical Product Path Guiding Using Linearly Transformed Cosines",
  journal      = "Computer Graphics Forum (Proceedings of the Eurographics Symposium on Rendering)",
  year         = "2020",
  url          = ""

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