Is it always true that what comes in must go out? Is it possible, say, some black material just absorbs the light and do little reflection (so that the energy transforms into thermal energy)?
It's not mentioned in the slide but you mentioned light actually bounces around several times inside skin, why is that the case?
In this case, the frequency of the incoming ray is not guaranteed to be the same when coming out. Do we have a mechanism to handle the frequency change and delete those out of the visible light spectrum?
Are there computational models simulating the last case?
Do we also model the other cases with a scattering function?
Different colors have different absorption of light. How to distinguish and calculate?
How do we distinguish the different cases of photon scattering? How do we know when it should behave for different materials/shapes?
Would scattering be modeled differently based on what perspective we were looking from, i.e. moving around in a VR?