Mobile Standard Lite - Bad SH Reconstruction
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Teeh
SDK 3.7.4
Using Pixar's Stylized HDRI "Env_Skylight", Mobile Standard Lite exhibits this weird black banding, similar but different to Filamented, which has had this fixed. I understand Mobile Standard Lite borrows from Filamented, so the fix may be similar.
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pema99
The issue seems to be in UnityGI_BaseVRC. The code samples L1 using the geomerics reconstruction, then adds the L2 contribution on top. If you comment out the highlighted line, the result will look more sensible, but you'll also lose the L2 contribution.
There are a few different ways of dealing with this:
- Ignore the issue.
- Don't add L2 contribution at all, accept the loss of fidelity.
- Don't use geomerics reconstruction for L1. The reason you get such a harsh band is because the L1 reconstruction shrinks the reconstructed lobe, leading to portions of the sphere where there is no longer a positive contribution from L1 to outweigh the large negative coefficients from L2. In other words, there is a mismatch in how you reconstruct each band.
- Apply a windowing function to the SH coefficients. Lancozs and hanning filters are pretty common for this (see image). Ideally you base the filter strength on the magnitude of the peak of the SH band, thats the basis for many deringing techniques (https://www.ppsloan.org/publications/shdering.pdf), but is a bit complicated. Using a constant strength also works for most cases, though, and basically just boils down to multiplying a positive constant onto the L2 contribution.