Fast Skin (misss)

 
 
 

| 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

Ambient Color

Controls the color of the ambient illumination component. The ambient component is included in the lightmap, and is scattered like other light.

Overall Color Multiplier

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.

Diffuse

The diffuse illumination component represents the top layer of skin, where tiny bumps and imperfections occur.

Color

Controls the color of the top layer of skin.

Weight

Controls the diffuse component's weight when the component is layered with the other illumination components (epidermal, subdermal, etc.).

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.

Color

Controls the color for the epidermal layer scattering.

Weight

Controls the weight of the epidermal scattering when it is blended with the other lighting components (diffuse, subdermal scattering, back scattering, etc.).

Radius

Controls the distance that light scatters along the epidermal layer. This value is measured in scene units, but is divided by the Scale value on the Advanced Settings tab.

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.

Color

Controls the color for the subdermal layer scattering.

Weight

Controls the weight of the subdermal scattering when it is blended with the other lighting components (diffuse, epidermal scattering, back scattering, etc.).

Radius

Controls the distance that light scatters along the subdermal layer. This value is measured in scene units, but is divided by the Scale value on the Advanced Settings tab.

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.

Color

Controls the color for the back surface scattering.

Weight

Controls the weight of the back scattering when it is blended with the other lighting components (epidermal scattering, subdermal scattering, diffuse, etc.).

Radius

Controls the distance that light scatters along the back surface. This value is measured in scene units, but is divided by the Scale value on the Advanced Settings tab.

Normally, the back scattering radius should be set to the same value as the back scattering Depth parameter.

Depth

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 Radius parameter.

Generally speaking, realistic skin does not require very high depth values.

Common Scatter Controls

Lightmap Samples

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.

Epidermal/Subdermal Sample Falloff

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 Radius value to compensate.

Bias

Allows you to bias the scattering in the rendered image in favor of either front scattering (positive values) or back scattering (negative values).

Specular

Weight

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.

Edge Factor

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.

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 Shinyness, low Weight, and a high Edge Weight.

Color

Controls the color of the top-layer specular highlights.

Weight

Controls the base weight of top-level specular highlights.

Edge Weight

This value is added to the specularity's overall weight to produce the top-layer specularity at the edges.

Shinyness

Modifies the size and sharpness of the top-layer specular highlights. Higher values cause smaller, sharper highlights and vice-versa.

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 Shinyness, medium Weight, and little or no Edge Weight.

Color

Controls the color of the second-layer specular highlights.

Weight

Controls the base weight of second -level specular highlights.

Edge Weight

This value is added to the specularity's overall weight to produce the second -layer specularity at the edges.

Shinyness

Modifies the size and sharpness of the second -layer specular highlights. Higher values cause smaller, sharper highlights and vice-versa.

Reflections

Weight

Controls the weight of reflections. Reflections are added to the object as soon as the value is set to something other than 0.

Edge Weight

Controls the edge-weight of reflections.

Shinyness

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.

Environment Only

When activated, no raytraced reflection are computed. Instead, reflections are generated using an environment shader applied to the render pass.

Advanced Settings

Lightmap

Group Name

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.

Size as % of output resolution

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.

Sampling Gamma

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.

Miscellaneous

Scale

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.

Use Screen Compositing for Colors

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.

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.