Can somebody help explain the mathematics of Sub Surface Scattering in a Path Tracer based on the Diffuse Approximation in A Practical Model for Subsurface Light Transport ?
I would like someone to explain the mathematics a little more clearly (why we need both the Fresnel terms, the diffusion profile, why we multiply everything by 1/π) and show me what I need to put together finally in Pseudocode. The symbols in all of the equations are also confusing (I'm still doing high school math), so any definition for each symbol would be great.
Along with that, I had a few simpler questions.
Why do we approximate the BSSRDF as a BRDF? Is it because the outgoing rays are usually isotropic? What are the main differences in mathematics between the original and approximation?
Can this BSSRDF approximation be importance sampled?
Currently I have an understanding of how everything works based on this post from a while back which is a good explanation. However, when it comes to implementation and all the overwhelming mathematics I get very confused. Can someone help me? I haven't been able to find a beginner friendly resource online so I hoped someone here could share their knowledge.