| Diffuse | Specular | Advanced Settings | Render Tree Usage
Category: Illumination
Shader Family: Material Phenomenon
Output: Custom
The Fast Skin Subsurface Scattering shader is a specialized and more complex variant of the Fast Simple (misss), and is designed to create realistic skin. It supports three levels of light scattering, two levels of specular highlights,
and glossy raytraced reflections. All of the scattering, illumination and specularity layers are added together to produce
the final skin effect.
Like the Fast Simple Subsurface Scattering shader, the Fast Skin shader supports bump mapping and displacement mapping. Although
these ports are not exposed in the shader's property editor, they appear in the shader's render tree node, allowing you to
connect bump and/or displacement shaders.
Note that if you connect a bump map to the bump map port, the bumping affects only the diffuse lighting component. This is
because the various levels of scattering take place below the object's surface, and are not affected by bump mapping.
NoteNote that fast subsurface scattering effects are not included in the maps generated by the RenderMap tool.
Diffuse
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Controls the color of the ambient illumination component. The ambient component is included in the lightmap, and is scattered
like other light.
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This color affects all of the underlying illumination components in the skin shader (unscattered, epidermal scattering, subdermal
scattering, back scattering). It is useful for making overall color adjustments to the final effect. You can also drive this
parameter with textures that are supposed to block light, such as moles or dirt.
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Diffuse
The diffuse illumination component represents the top layer of skin, where tiny bumps and imperfections occur.
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Controls the color of the top layer of skin.
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Controls the diffuse component's weight when the component is layered with the other illumination components (epidermal, subdermal,
etc.).
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Epidermal Scatter
The epidermal scattering component represents the layer of skin just below the surface. It is considered a "front-scattering"
component, meaning that its effect is most visible when the front side of the object is lit.
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Controls the color for the epidermal layer scattering.
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Controls the weight of the epidermal scattering when it is blended with the other lighting components (diffuse, subdermal
scattering, back scattering, etc.).
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Controls the distance that light scatters along the epidermal layer. This value is measured in scene units, but is divided
by the value on the Advanced Settings tab.
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Subdermal Scatter
The subdermal scattering component represents the layer of skin beneath the epidermal layer. It is also considered a "front-scattering"
component, meaning that its effect is most visible when the front side of the object is lit. However, the subdermal layer
produces a deeper scattering than the epidermal layer.
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Controls the color for the subdermal layer scattering.
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Controls the weight of the subdermal scattering when it is blended with the other lighting components (diffuse, epidermal
scattering, back scattering, etc.).
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Controls the distance that light scatters along the subdermal layer. This value is measured in scene units, but is divided
by the value on the Advanced Settings tab.
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Back Scatter
The back scattering component represents the light going through the object. Back scattering is most visible when the object
is backlit to some extent, or when light passes directly through the object. For example, back scattering is largely responsible
for the red glow that you see if you shine a flashlight through your hand.
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Controls the color for the back surface scattering.
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Controls the weight of the back scattering when it is blended with the other lighting components (epidermal scattering, subdermal
scattering, diffuse, etc.).
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Controls the distance that light scatters along the back surface. This value is measured in scene units, but is divided by
the value on the Advanced Settings tab.
Normally, the back scattering radius should be set to the same value as the back scattering parameter.
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Controls the back scatter depth. The higher the value, the more deeply light is scattered within the object. In effect, raising
the depth makes the object appear more translucent, especially when backlit.
Normally, the back scattering depth should be set to the same value as the back scattering parameter.
Generally speaking, realistic skin does not require very high depth values.
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Common Scatter Controls
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Specifies the number of lightmap samples considered by each rendered ray. Generally, this should be set to a power of two
(16, 32, 64, 128, etc.).
Subtle scattering effects typically require few samples. However, as you begin to increase the front and back scattering radii,
or the back scattering depth, you will need to increase the number of samples to avoid speckling in the rendered image.
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Defines the falloff profile for light scattered along the epidermal radius. Higher values cause a sharper falloff. Lower values
cause a smoother falloff but cause the scatter distance to appear shorter, though you can increase the value to compensate.
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Allows you to bias the scattering in the rendered image in favor of either front scattering (positive values) or back scattering
(negative values).
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Specular
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Controls the overall level of specularity and reflections. This is where you would connect a specular map, which will affect
the primary and secondary specular highlights as well as the reflections.
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Controls the width of edge reflections caused by the Fresnel effect (the effect that causes skin when viewed from a perpendicular
angle).Higher values cause the edge to become thinner and vice versa.
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Primary
The primary specular highlight defines the skin's top layer of specular highlights, which are most visible where the skin
is wet or oily. Normally, the primary specularity should have low low and a high .
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Controls the color of the top-layer specular highlights.
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Controls the base weight of top-level specular highlights.
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This value is added to the specularity's overall weight to produce the top-layer specularity at the edges.
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Modifies the size and sharpness of the top-layer specular highlights. Higher values cause smaller, sharper highlights and
vice-versa.
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Secondary
The secondary specular highlight defines the skin's second layer of specular highlights, which are typically wider and softer
than the top-layer highlights. Normally, the secondary specularity should have high medium and little or no .
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Controls the color of the second-layer specular highlights.
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Controls the base weight of second -level specular highlights.
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| Edge Weight
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This value is added to the specularity's overall weight to produce the second -layer specularity at the edges.
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Modifies the size and sharpness of the second -layer specular highlights. Higher values cause smaller, sharper highlights
and vice-versa.
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Reflections
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Controls the weight of reflections. Reflections are added to the object as soon as the value is set to something other than
0.
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Controls the edge-weight of reflections.
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When this value is set to 0, normal raytraced reflections are used. When the value is greater than 0, glossy reflections,
which take longer to render, are used.
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When activated, no raytraced reflection are computed. Instead, reflections are generated using an environment shader applied
to the render pass.
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Advanced Settings
Lightmap
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The name of the "scatter group" that the shaded object belongs to. All objects that can scatter light into one another should
belong to the same scatter group.
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Specifies the size of the lightmap, expressed as a percentage of the final rendered image resolution. Normally, this value
should not need to be higher than 50%. However, should the rendered image still contain artifacts, you can set it higher than
this.
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This is a gamma curve for the light stored in the lightmap. Values of less than 1 cause light to spread perpendicularly to
the lighting direction. Values greater than 1 cause light to concentrate in areas facing the light source itself.
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Miscellaneous
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This is a conversion factor used to convert the scene's distance units into the shader's distance units. This is useful when
you reuse one object's material on another object that was built using different units.
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Normally, all of the light layers computed by the skin shader are added together to produce the final skin effect. Turning
this option on blends the layers together using a Screen compositing mode, which creates a softer result.
This is especially useful when the combination of the lighting layers creates too bright a result, creating overexposed white
patches on the object.
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Render Tree Usage
The fast skin shader is a material phenomenon - a predefined combination of shaders packaged into a single node. It is plugged
directly into the Material node's Material port, which prevents the material node from accepting other connections. You can
extend the phenomenon's effect by driving its parameters with other shaders. Note that this shader's render tree node has
bump and displacement inputs that have no corresponding parameters in the property editor. Bump and displacement shaders can
be connected to these ports to add bump and/or displacement mapping to the object's surface.
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