Abstract: This technical memo compares six different strategies for sampling a disk area light source. We test padding the domain with zero values, rejection sampling, polar mapping, concentric mapping, and two new strategies we call polar4 and concentric4 mapping. We test the six strategies with nine different sample sequences on pixels with full illumination and partial shadow (penumbra), and find the best combination of sampling strategy and sample sequence. One of the new sampling strategies gives more than 3 times error reduction in some cases.

One-line summary: With the right sampling strategy and stratification, illumination from disk lights can converge (nearly) as fast as illumination from square lights.

Published as: Pixar Technical Memo #18-02. Pixar, June 2018.

Download the tech memo here: paper.pdf.

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