The overall intensity of the scattering effect.
Controls the nature of the scattering. Positive values give forward scattering,
0 gives isotropic scattering, and negative values give backscattering. Range is
-1 (full backscattering) to
1 (full forward scattering).
The value depends on the type of material you are trying to model. For example, skin is highly forward scattering, while marble is backscattering.
The minimum intensity that is not blended using fresnel values.
Absolute index of refraction of the surface medium (the physical material the shader is simulating the look of).
Absolute index of refraction of the surrounding medium (for example, air).
See the list of indices for various materials .
This is the dominant color that will appear in lit areas of the surface.
How quickly the light intensity decreases as it scatters. Higher values make the lighting level decrease faster. Available when Parameter mode is Artist.
The color the surface will tend toward in unlit areas. This value adjusts the density so that the color components with higher attenuation color values will scatter light at longer distances, while color components with a low attenuation color will scatter at shorter distances. Available when Parameter mode is Artist.
Enable/disable contribution from light that scatters exactly once in the surface. Certain types of surfaces (such as skin) gain little contribution from single scattering and so disabling this option will reduce computation time with little impact on accuracy.
Intensity of single scattering.
The number of samples for single scattering. Increase this option to decrease noise at the expense of slower shading.
Enable contribution from light that scatters more than once in the surface. For low albedo materials (low Diffuse Color), multiple scattering contributes little to the image and can be disabled to reduce computation time.
Intensity of multiple scattering.
The quality of the light sampling used for the point cloud contribution when Model is Global Point Cloud or Local And Global. This value is also used to control the number of ray samples when the Model is Ray Tracing.
Controls the way in which multiple scattering is computed. Normally you should use the Local And Global mode if you are planning to use a point cloud, and Ray Tracing to compute multiple scattering without a point cloud. Using a point cloud can produce smoother and faster results, but it requires precomputation of a point cloud and computation of irradiance for each point in the cloud (once per render).
Use ray tracing rather than a point cloud to approximate multiple scattering. This option avoids point cloud calculations but may require more sampling to eliminate noise.
Full Ray Tracing
When an single object is made of multiple packed primitives (i.e. multiple Alembic shape nodes), each shape will have local multiple scattering. With Full Ray Traced, all individual packed primitives will be considered when computing multiple scattering.
Only use a BRDF function to compute the multiple scattering contribution. This is the fastest option, though no subsurface diffusion will be produced.
Global Point Cloud
Use a point cloud to compute the multiple scattering contribution. This option requires a precomputation stage to generate the point cloud and to calculate and cache the surface irradiance values in the point cloud.
Local And Global
Use the BRDF function to compute the local contribution and the point cloud to compute the global contribution, with the Local Radius Scale parameter controlling the local radius. This option will usually produce more accurate results than using a point cloud alone, especially for short scattering distances.
Simulate subsurface scattering by path tracing through it as a volume. This options is slow and noisy but will produce the most accurate results - so it may be used to produce ground truth images for comparison with the other techniques.
Controls the file the point cloud is written to/read from when Point Cloud Mode is Write To File or Read From File. The point cloud is based on surface UVs, so it is not necessary to write a new point cloud file for each frame unless the topology of the model is changes.
Point Cloud Mode
Controls how the shader generates a point cloud. The simplest option is to select Generate At Render Time. This will create a new point cloud for every render. To reduce computation time, you can first use Write To File mode and then re-use the point cloud using Read From File mode on subsequent renders. This is also the recommended approach when rendering animations because the shader will smoothly interpolate the point cloud across frames. The exception to this is when the model’s topology changes (two joined polygons are separated, for example). In this case, a new point cloud must be generated. Note that in Write To File mode, the file will be overwritten if it already exists. Cancelling a render before it completes in Write To File mode may result in an unusable point cloud file.
See managing point clouds for more information.
Generate At Render Time
Always regenerate the point cloud whenever the node renders. This is convenient since you don’t have to worry about file management, and can be useful when you are modifying the shader and model at the same time. However, for efficiency you should cache the point cloud, especially when rendering animation.
Read From File
Read the point cloud from a file (specified in the Point Cloud parameter below), generated using the Write To File mode.
Write To File
Write the point cloud to the file specified in the Point Cloud parameter below.