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The assumption underlying such model is the same as lots of other models for skin rendering; the subsurface scattering can be approximated as a diffusion phenomenon. This is good because in highly scattering media, the distribution of light loses dependency from the angle and tends to isotropy. The dipole approximation is a formulation for the resolution ...

8

As mentioned in the comments, I would highly suggest starting with Full Volumetric Scattering. This is two fold: Since you are doing path tracing, adding volumetrics isn't super difficult. Fully understanding how full volumetric scattering works will be a great basis for understanding the estimations. In addition, it can provide great "references" to see if ...

8

There are lots of ways to fake SSS with greater or lesser fidelity. A few recent-ish methods: Screen-space blurring of object lighting (described in detail here) Using “interior” ambient-occlusion maps generated from a normal-flipped version of the geometry to approximate local thickness, providing an easy way to fake light transmission (more information ...

6

You want to use the "conductor" plugin to create a smooth conductor / metal type BRDF. See section 8.2.6 in the documentation. As far as Mitsuba is concerned, a mirror is a special instance of a metal, where the material is specified as "none" (which corresponds to using complex IOR of $\eta = 0$ and $k = 1$). Here is an example in xml: <shape type=...

6

The goal of Heitz et al.'s model is pretty much the opposite of subsurface scattering: They only consider surface scattering, i.e. the ray can never enter the material. Because microfacets are statistical in nature, they can recast their problem in such a way that it can be solved by microflakes, which allows them to compute properties such as the mean free ...

4

For cases where the diffusion approximation is preferred over full volumetric path tracing, the method published by Solid Angle is fairly efficient: https://www.solidangle.com/research/s2013_bssrdf_slides.pdf It is implemented in the Arnold render engine, Blender's Cycles, and pbrt, the latter being open source. The file which implements it in PBRT is here:...

3

To easily understand the 'dipole theory' we have first to understand from where it comes from the 'diffusion theory'. And it comes from simulating light transport in participating media by solving the radiance transport equation (RTE). The classical diffusion approximation solves the RTE by considering only a first-order spherical harmonic expansion of the ...

2

The heading row of Figure 5(b) says that the units of $\sigma_s'$ and $\sigma_a$ are inverse millimetres, that is, inverse distance. Hence, $1/\sigma_t'$ has units of distance. If you send a beam of photons through a medium with scattering coefficient $\sigma$ and measure it at distance $l$, then the probability that a photon has made it that far without ...

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