Consider anisotropy in multi-scatter to single-scatter albedo conversion#42
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bsdorra wants to merge 2 commits into
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Consider anisotropy in multi-scatter to single-scatter albedo conversion#42bsdorra wants to merge 2 commits into
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…em flawed. In particular, I think formula 80 for computing \rho_{ss} is not correct enough.
Formula 80 is taken from the referenced talk (https://blog.selfshadow.com/publications/s2017-shading-course/imageworks/s2017_pbs_imageworks_slides_v2.pdf), slide 44. But the formula in the spec is a simplification of the formulas on slide 44, assuming that g = 0. I believe this simplification was valid for DSPBR 2019x, where g could not be changed and was instead fixed to 0. But since DSPBR 2021x, this assumption is not valid anymore - and it seems that the Stellar implementation actually complies with the proposed correction.
Therefore I propose this extension which corrects the over-simplification
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Nice catch. Looks like the spec update slipped through the cracks. Minor suggestion: The parameter g isn't introduced until much later. Since we are now using it at the beginning of the section, its introduction should move up too.
Introduce anisotropy parameter g before its use in the single-scattering albedo conversion. Consolidate its explanation near the phase function and remove the duplicate isotropic conversion from the 2022x spec.
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PR on behalf of @JMeseth:
The formulas for the volumetric layer in DSPBR from the DSPBR spec seem flawed. In particular, I think formula 80 for computing \rho_{ss} is not correct enough.
Formula 80 is taken from the referenced talk (https://blog.selfshadow.com/publications/s2017-shading-course/imageworks/s2017_pbs_imageworks_slides_v2.pdf), slide 44. But the formula in the spec is a simplification of the formulas on slide 44, assuming that g = 0. I believe this simplification was valid for DSPBR 2019x, where g could not be changed and was instead fixed to 0. But since DSPBR 2021x, this assumption is not valid anymore - and it seems that the Stellar implementation actually complies with the proposed correction.
Therefore I propose this extension which corrects the over-simplification