SSS 2

The SSS 2 node allows you to create translucent materials like skin, marble etc.This material only has the sub-surface scattering component.

Diffuse Reflectance - The color of the diffuse portion of the material.

Scatter Radius - The internal scattering color for the material. Brighter colors cause the material to scatter more light and to appear more translucent; darker colors cause the material to look more diffuse-like.

Scatter Radius Mult - Controls the amount of light scattering in the material. Smaller values cause the material to scatter less light and to appear more diffuse-like; higher values make the material more translucent. Note that this value is specified always in centimeters (cm); the material will automatically convert it into scene units based on the currently selected system units.

Subdivs - Controls the quality of the SSS effect. Higher values reduce the noise and increase render times. This parameter has effect only when the Use Local Subdivs option is enabled from the Global DMC Sampler Settings.

Scale - Scales the subsurface scattering radius additionally.  

Phase Function - A value between -1.0 and 1.0 that determines the general way light scatters inside the material. Its effect can be somewhat likened to the difference between diffuse and glossy reflections from a surface, however the phase function controls the reflection and transmittance of a volume. A value of 0.0 means that light scatters uniformly in all directions (isotropic scattering); positive values mean that light scatters predominantly forward in the same direction as it comes from; negative values mean that light scatters mostly backward. Most water-based materials (e.g. skin, milk) exhibit strong forward scattering, while hard materials like marble exhibit backward scattering. This parameter affects most strongly the single scattering component of the material. Positive values reduce the visible effect of single scattering component, while negative values make the single scattering component generally more prominent.

IOR - The index of refraction for the material. Most water-based materials like skin have IOR of about 1.3.

Max Distance - Each sample is represented by a circle in the final image. This parameter allows the user to specify the radius of the sample.

Prepass

V-Ray uses a pre-pass similar to the Irradiance Map in order to generate the SSS effect. These parameters allow you to set up the pre-pass.

Rate - SSS 2 accelerates the calculation of multiple scattering by precomputing the lighting at different points on the surface of the object and storing them in a structure called an illumination map, which is similar to the irradiance map used to approximate global illumination, and uses the same prepass mechanism built into V-Ray that is also used for e.g. interpolated glossy reflections/refractions. This parameter determines the resolution at which surface lighting is computed during the prepass phase. A value of 0 means that the prepass will be at the final image resolution; a value of -1 means half the image resolution, and so on. For high quality renders it is recommended to set this to 0 or higher, as lower values may cause artifacts or flickering in animations. If the chosen prepass rate is not sufficient to approximate the multiple scattering effect adequately, SSS 2 will replace it with a simple diffuse term. This can happen, for example, for objects that are very far away from the camera, or if the subsurface scattering effect is very small. This simplification is controlled by the Blur parameter.

Blur - Controls if the material will use a simplified diffuse version of the multiple scattering when the prepass rate for the direct lighting map is too low to adequately approximate it. A value of 0.0 will cause the material to always use the illumination map. However, for objects that are far away from the camera, this may lead to artifacts or flickering in animations. Larger values control the minimum required samples from the illumination map in order to use it for approximating multiple scattering.

ID - Тhis option allows several SSS2 materials to share the same illumination map. This could be useful if you have different SSS 2 materials applied on the same object.If this is greater than 0, then all materials with the specified ID will share the same map.

Geormetry based sampling - Аllows the user to control how the subsurface effect is sampled. When disabled the sampling is done based on the resolution of the image. If this option is enabled the sampling is done uniformly based on the size of the geometry. This mode ensures an even sample distribution that is not affected by the camera perspective, which in turn fixes flickering in animations.

Samples per unit area - Has effect only when the Auto calculate density check box is disabled. It allows you to control the number of samples that are going to be taken for each square unit of the geometry surface. The size of one unit is controlled by the 3ds Max scene units set up. Increasing this parameter means that more samples are going to be taken which produces higher quality results at the cost of increased render times.

Preview samples - When this option is enabled, V-Ray renders an image that displays the samples distribution along the surface of the geometry. It can be used for debugging artifacts much like the show samples parameter of the Irradiance Map.

Surface offset - To prevent artifacts, each sample is taken a tiny distance away from the actual surface in the direction of the normal. This parameter controls that offset.

Scatter GI - Controls whether the material will accurately scatter global illumination. When off, the global illumination is calculated using a simple diffuse approximation on top of the sub-surface scattering. When on, the global illumination is included as part of the surface illumination map for multiple scattering. This is more accurate, especially for highly translucent materials, but may slow down the rendering quite a bit.

Single Scatter - Enables the multiple scattering component for light that falls on the same side of the object as the camera.

Back Scatter - Enables the multiple scattering component for light that falls on the opposite side of the object as the camera. If the material is relatively opaque, turning this off will speed up the rendering.

Linear Workflow - When enabled the revers gamma will be applied to all colors and textures used in the material.