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Example: Sub Surface Color

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

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.

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Sub Surface Color = Red

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Sub Surface Color = Green

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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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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.

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Example: Scatter Color

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

The Sub-surface color is kept to green.

 

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Scatter Color = Red

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Scatter Color = Green

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Scatter Color = Blue


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

 

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Scatter radius - 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.

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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.

This set of images is based on the Milk (skimmed) preset.

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

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Scatter Radius = 1.0cm

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Scatter Radius = 2.0cm

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Scatter Radius = 2.0cm

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Scatter Radius = 4.0cm

4.0cm

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

 

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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.

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Example: Phase Function

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.

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

Phase Function = -0.5 (Backward Scattering)

 

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


Phase Function = 0 (Isotropic Scattering)

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Phase Function = 0.0 (Forward Scattering)
More light is absorbed object. 

Phase Function = 0.0 (Forward Scattering)
More light is absorbed object. 

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Phase Function = 0.5 (Forward Scattering)

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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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Example: Phase Function: Light Source

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.
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Phase Function = -0.9

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Phase Function = 0

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Phase Function = 0.0

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Example: Single Scatter Mode

This example shows the effect of the Single scatter mode parameter.

For relatively opaque materials, the different Single scatter modes produce quite similar results (except for render times). In the following set of images, the Scatter radius is set to 0.5 cm.

In the second set of images, the Scatter radius is set to 50.0 cm. In this case, the material is quite transparent, and the difference between the different Single scatter modes is apparent. Note also the transparent shadows with the Raytraced (refractive) mode.

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Single Scatter = Simple

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Single Scatter = Ray Traced Solid

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Single Scatter = Ray Traced Refractive

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Single Scatter = Simple

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Single Scatter = Ray Traced Solid

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Single Scatter = Ray Traced Refractive

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

 

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Scatter subdivs - determines the number of samples to make when evaluating the single scattering component when the Single scatter mode is set to Raytraced (solid) or Raytraced (refractive).

Refraction depth - this determines the depth of refraction rays when the Single scatter parameter is set to Raytraced (refractive) mode.

Front lighting - enables the multiple scattering component for light that falls on the same side of the object as the camera.

Back lighting - 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.

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.

Cut-off threshold - this is a threshold below which reflections will not be traced. V-Ray tries to estimate the contribution of reflections to the image, and if it is below this threshold, these effects are not computed. Do not set this to 0.0 as it may cause excessively long render times in some cases.

Prepass 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.

 

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Example: Color Changes Inside the Material

This example demonstrates how the apparent color of the material might change inside of objects. In the first set of images, the Scatter color is set to grey, while the Sub-surface color changes between red, green and blue. Note how the part of the surface that is directly lit appears with the Sub-surface color, while the portion of the object away from the light gradually blends into darkness. This is because the light colors specified by the Sub-surface color parameter are scattered out of the material near the surface, and only the remaining light passes through. (To better demonstrate this effect, the Single scatter mode is set to Raytraced (solid) for all images in this example.)

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The Sub-surface color is red (RGB 218, 58, 58)

and the Scatter color is grey.

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The Sub-surface color is green (RGB 58, 218, 58)

and the Scatter color is grey.

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The Sub-surface color is blue (RGB 58, 58, 218)

and the Scatter color is grey.

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This effect becomes less apparent if the colors are more saturated, as demonstrated in the following set of images:

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The Sub-surface color is red (RGB 218, 13, 13)

and the Scatter color is grey.

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The Sub-surface color is green (RGB 13, 218, 13)

and the Scatter color is grey.

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The Sub-surface color is blue (RGB 13, 13, 218)

and the Scatter color is grey.

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If this effect is not desired, the Scatter color should be modified. In the set of images below, the Sub-surface color is set as before, and in addition, the Scatter color is set to a more saturated version of the same color.

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The Sub-surface color is (RGB 218, 58, 58),

and the Scatter color is (RGB 218, 13, 13).

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The Sub-surface color is (RGB 58, 218, 58),

and the Scatter color is (RGB 13, 218, 13).

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The Sub-surfacecolor is (RGB 58, 218, 58),

and the Scatter color is (RGB 13, 218, 13).

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