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.
Copyright (©) 1986-2008 by
mental images GmbH