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maria-taher
07-08-2011, 12:19 PM
Hi

I will learn SSS in Mental Ray and in here is two type of SSS : "SSS fast shader" and "SSS physical"

what is advantage of each?

doctorcillo
07-08-2011, 12:48 PM
The Fast subsurface scattering shaders do not simulate true volumetric scattering but the "appearance" of scattering. They are producing a reasonable, visually pleasing, easy to use, consistent looking result that is free of artifacts, and have good frame-to-frame coherence (no flickering). One of the design goals of these shaders is to provide a way to efficiently render human skin.

The misss_physical (http://forums.cgsociety.org/) shader simulates subsurface scattering in a physically correct way. The shader need to be used both in the material and photon shader slots of a material.
This shader performs three kinds of simulations which can be used together or independently:

Multiple-scattering estimationthe most accurate, uses a strictly deterministic simulation of photon tracing to record sites in an internal photon map. These sites are looked up at render time and an optimized ray marching technique estimates multiple scatter irradiance.Single-scattering approximationis based on light intensities, independent of photon mapping.Diffusion theoryis applied to evaluate the contribution of photons in the deep layer. The following scattering features are supported:




Simulate subsurface scattering materials both in still images and animations (although the fast shaders may be more suitable for animation).
Receive and continue subsurface scattering media caustics from the outside world.
Cast caustics from the subsurface scattering media to the outside world.
Specify both absorption and scattering coefficients. The resulting image will simulate correctly areas of absorption and areas of scattering. This is very important to get subtle color changes for example in milk from blue to yellow.
Perform scattering along the geometry.

All above was taken from Maya's Documentation.
You should have a look at it for further information.

Hope it helps anyway.

maria-taher
07-08-2011, 01:39 PM
Thanks doctorcillo.

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