Recently I’m learning about Pre-Integrated Skin, and feel confused with how Unreal generate the BRDF look-up table texture.
It looks very different with the BRDF LUT in Penner pre-integrated skin rendering (siggraph 2011 advances in real-time rendering course).
Unreal version does a normal lambert diffuse first, then sample from the BRDF LUT and combine the result.
Penner version directly sample from the BRDF LUT as the result of scattering.
Penner version LUT
Unreal version LUT
I want to know how to generate unreal version Pre-Integrated skin BRDF LUT.