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I am writing a pathtracer, and I want to somehow incorporate importance sampling of the environment map. The obvious way to do this seems to use MIS to either importance sample from my material bsdf or a ray to my environment map. I am having a hard time making it work though, and I am feeling uncertain as to whether I can really say that it is unbiased.

The main problem I have is that if I have a very bright environment light on the opposite side of the material, it will pretty much be sampled at least 50% of time time according to MIS. I should know that sampling that direction won't contribute to reducing variance in any way, as the brdf in that direction is 0. But how can I incorporate this into my MIS "flow" while keeping it completely unbiased???

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  • $\begingroup$ You could add a third sampling strategy that samples in the general direction of that bright light (e.g., a spherical Gaussian) and compute the MIS weights accordingly. This will remain unbiased. $\endgroup$
    – Hubble
    Commented Nov 21 at 19:36

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