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UI Path: ||Toolbar|| > V-Ray menu icon > Materials > VRayMtlSSS

 

 

General

 

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Preset – Allows you to choose one of several available preset materials. Most of the presets are based on measured data provided by by Jensen et al. in [ 3 ] in A Practical Model for Subsurface Light Transport.

Scale – Additionally scales the subsurface scattering radius. Normally, VRayMtlSSS will take the scene units into account when calculating the subsurface scattering effect. However, if the scene was not modeled to scale, this parameter can be used to adjust the effect. It can also be used to modify the effect of the presets, which reset the Scatter radius parameter when loaded, but leave the Scale parameter unchanged. For more information, see the Scale example below. 

Index of Refraction – The index of refraction for the material. Most water-based materials like skin have an index of refraction of about 1.3.

 

 

 



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Example: VRayMtlSSS Presets

 


Section
Column


Skin Brown

 


Column


Skin Pink

 


Column


Skin Yellow

 


Column


Milk [Skim]

 


Column


Milk [Whole] 


Section
Column


Marble [White]

 


Column


Ketchup

 


Column


Cream 


Column


Potato 


Column


Spectralon

 

 



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scale
scale

Example: Scale

 


This example shows the effect of the Scale parameter. Note how larger values make the object appear more translucent. In its effect, this parameter does essentially the same thing as the Scatter radius parameter, but it can be adjusted independently of the chosen preset. The images are rendered without GI to better show the sub-surface scattering. The Single scatter parameter was set to Raytraced (solid). The Marble (white) preset was used for all images.

 


Section
Column


Scale = 1

 


Column


Scale = 10 


Column


Scale = 100 



 
 


Diffuse and SSS Layers

 

 


Overall Color – Controls the overall coloration for the material. This color serves as a filter for both the diffuse and the sub-surface component.

Diffuse Color – The color of the diffuse portion of the material.

Diffuse Amount – The amount for the diffuse component of the material. Note that this value in fact blends between the diffuse and sub-surface layers. When set to 0.0 , the material does not have a diffuse component. When set to 1.0 , the material has only a diffuse component, without a sub-surface layer. The diffuse layer can be used to simulate dust etc. on the surface.

Sub-surface Color – The general color for the sub-surface portion of the material. For more information, see the Sub Surface Color example below. 

Scatter Color – 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. For more information, see the Scatter Color example below. 

Scatter radius (cm) – 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 take care to convert it into scene units based on the currently selected system units. For more information, see the Scatter Radius example below. 

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. For more information, see the Phase Function example and the Phase Function: Light Source example below. 

 


Anchor
subSurfaceColor
subSurfaceColor

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Example: Sub Surface Color

 


This example and the next demonstrate the effect of and the relation between the Scatter color and the Sub-surface color parameters. Note how changing the Sub-surface color changes the overall appearance of the material, whereas changing the Scatter color only modifies the internal scattering component.

The Scatter color is set to green.

 


Section
Column


Sub Surface Color = Red

 


Column


Sub Surface Color = Green

 


Column


Sub Surface Color = Blue 



Note: the "happy buddha" model is from the Stanford scanning repository (http://graphics.stanford.edu/data/3Dscanrep/).

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scatterColor
scatterColor
 

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Example: Scatter Color

 


The Sub-surface color is kept to green.

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Section
Column


Scatter Color = Red 


Column


Scatter Color = Green

 


Column


Scatter Color = Blue 



Note: the "happy buddha" model is from the Stanford scanning repository (http://graphics.stanford.edu/data/3Dscanrep/).

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scatterRadius
scatterRadius

 

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Example: Scatter Radius


This example shows the effect of the Scatter radius parameter. Note that the effect is the same as increasing the Scale parameter, but the difference is that the Scatter radius is modified directly by the different presets.

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The cube in the lower left corner has a side of 1cm.

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Section
Column


Scatter Radius = 1.0cm 


Column


Scatter Radius = 2.0cm

 


Column


Scatter Radius = 4.0cm

 



Note: the "happy buddha" model is from the Stanford scanning repository (http://graphics.stanford.edu/data/3Dscanrep/).

 


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phaseFunction
phaseFunction

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Example: Phase Funciton

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This example shows the effect of the Phase function parameter. This parameter can be likened to the difference between diffuse reflection and glossy reflection on a surface, however it controls the reflectance and transmittance of a volume. Its effect is quite subtle, and mainly related to the single scattering component of the material.

The red arrow represents a ray of light going through the volume; the black arrows represent possible scattering directions for the ray.

 


Section
Column


Phase Function = -0.9 (Backward Scattering)
More light comes out. 


Column


Phase Function = 0 (Isotropic Scattering)
More light exits object. 


Column


Phase Function = 0.5 (Forward Scattering)
More light is absorbed object. 


Section
Column


Phase Function = -0.5 (Backward Scattering)

 


Column


Phase Function = 0 (Isotropic Scattering)

 


Column


Phase Function = 0.5 (Forward Scattering)

 



Note: the "happy buddha" model is from the Stanford scanning repository (http://graphics.stanford.edu/data/3Dscanrep/).

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lightSource
lightSource

 

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Example: Phase Function: Light Source

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This example demonstrates the effect of the Phase function parameter when there is a light source inside the volume. The images are based on the Skin (pink) preset with large Scatter radius and Raytraced (refractive) mode for single scattering with IOR set to 1.0. Front lighting and Back lighting are disabled for these images; only single scattering is visible. Note the volumetric shadows cast by the light inside the volume.

 


Section
Column


Phase Function = -0.9

 


Column


Phase Function = 0 


Column


Phase Function = 0.5

 

 

 



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Specular Layer Parameters

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Note: the "happy buddha" model is from the Stanford scanning repository (http://graphics.stanford.edu/data/3Dscanrep/).

 

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References
References
References

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Fancy Bullets
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Here is a list of links and references used when building the VRayMtlSSS material.

  • [1] H. C. Hege, T. Hollerer, and D. Stalling,   Volume Rendering: Mathematical Models and Algorithmic aspects
    An online version can be found at at http://www.cs.ucsb.edu/~holl/publications.html
    Defines the basic quantities involved in volumetric rendering and derives the volumetric and surface rendering equations.
  • [2] T. Farrell, M. Patterson, and B. Wilson,   A Diffusion Theory Model of Spatially Resolved, Steady-state Diffuse Reflectance for the Noninvasive Determination of Tissue Optical Properties in vivo , Med. Phys. 19(4), Jul/Aug 1992
    Describes an application of the diffusion theory to the simulation of sub-surface scattering; derives the base formulas for the dipole approximation used by Jensen et al. (see below).
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    [3] H. Jensen, S. Marschner, M. Levoy, and P. Hanrahan,   A Practical Model for Subsurface Light Transport, SIGGRAPH'01: Computer Graphics Proceedings, pp. 511-518
    An online version of this paper can be found at http://www-graphics.stanford.edu/papers/bssrdf/
    Introduces the concept of BSSRDF and describes a practical method for calculating sub-surface scattering based on the dipole approximation derived by Farrell et al. (see above).
  • [4] H. Jensen and J. Buhler,   A Rapid Hierarchical Rendering Technique for Translucent Materials, SIGGRAPH'02: Computer Graphics Proceedings, pp. 576-581
    An online version of this paper can be found at http://graphics.ucsd.edu/~henrik/papers/fast_bssrdf/
    Introduces the idea of decoupling the calculations of surface illumination and the sub-surface scattering effect in a two-pass method; describes a fast hierarchical approach for evaluating subsurface scattering and proposes a reparametrization of the BSSRDF parameters for easier user adjustment.
  • [5] C. Donner and H. Jensen,   Light Diffusion in Multi-Layered Translucent Materials, SIGGRAPH'05: ACM SIGGRAPH 2005 Papers, pp. 1032-1039
    An online version of this paper can be found at http://graphics.ucsd.edu/~henrik/papers/layered/layered.pdf
    Provides a concise description of the original BSSRDF solution method presented by Jensen et al; extends the model to multi-layered materials and thin slabs using multipole approximation.