Tuning

Properties of the algorithm control the quality and complexity of the rendering. The calculation of subsurface scattering is broken into three components: single scatter, multiple scatter, and diffusion. Depending on the optical properties of the material, the contributions of each component may dominate or be negligible. An important factor in determining this is the mean free path length of the material. This is the average distance a photon will travel in the material without scattering or absorption and is equal to the reciprocal of the sum of the scattering and absorption coefficients.

depth: The shader uses two different ways to scatter photons. After a certain number of scatterings a photon is scattered less precisely, yet faster. The depth determines how many scattering events are done using the precise scattering. The precise scattering is also called "shallow layer". The depth determines the end of the shallow layer and the begin of the deep layer.
max_samples: is the maximum number of samples evaluated by the single and multiple scatter components. Typical values range between 10 and 30.
max_photons: is the maximum number of photons to sample per lookup. It is similar to the global illumination accuracy parameter. Typical values range between 100 to 1000. Values up to 5000 are useful for scenes with uneven photon distribution.
max_radius: is the maximum radius of a sphere centered at a sample point from which to collect photons. It is similar to the global illumination accuracy radius. Typical values are a small percentage of the total size of the object.
approx_diffusion: this switch turns the diffusion component of the calculation on or off. Usually it should be on.
approx_single_scatter: this switch turns the single scatter component of the calculation on or off. Usually it should be on.
approx_multiple_scatter: this switch turns the multiple scatter component of the calculation on or off. Usually it should be on.
lights: list of lights directly linked to this shader.
mode: determines which lights should be used, see light lists.