misss_fast_simple

Category: mental ray > Material Phenomena

Shader Family: Material Phenomenon

Output: Custom

This phenomenon automatically (unless explicitly specified) generates the required lightmaps, fills in the lightmap data, and shades the objects as a general, translucent object with subsurface scattering. The scattering is divided into two parts, one for the front side of the object and one for the back. It is connected directly to the Material node's Material port, which prevents the material node from accepting other connections.

The shader works by layering several light contributions on top of each other (see misss_fast_shader for details) to get a final result. What is important to keep in mind are these rules of thumb:

The bump map only affects the specular and diffuse_color layers. The subsurface scattering happens below the surface and is oblivious to the surface having bumps.
The overall_color affects all of the diffuse contributions, but not the specularity.

For more information about building subsurface scattering effects in the render tree, see Fast Subsurface Scattering Effects [Materials and Shaders].

To simulate human skin, you can use misss_fast_skin_phen which are specialized and more complex variants of misss_fast_simple_phen.

Name	The name of the shader node displayed in the render tree. Enter any name you like, or leave the default.
lightmap depthmap	Not normally used because this phenomenon automatically generates lightmaps. These are special parameters the shaders use to communicate the name of the automatically created lightmaps between themselves. Expert users can pass writable textures and leave the lightmap_group and lightmap_size parameters undefined. You can Edit the image clip, or get a New image clip from file or from source. For more information about working with images, see Managing Image Sources & Clips [Data Management].
lightmap_group	The name of the scatter group. A lightmap and depthmap pair are created internally and given this name. All objects that should scatter light into each other should be in the same scatter group. To conserve memory, use as few scatter groups as possible. A character's hands, face, etc. can use the same scatter group; even hands and faces of different people. In general, different scatter groups should be used only when using the same group would cause visible problems due to objects incorrectly scattering into each other. Two characters shaking hands, for example, would need to have their hands in different scatter groups.
lightmap_size	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.
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.
bump	Pick the shader that perturbs the normals. The shader's color output (if any) will not be used.

d (diffuse)

ambient	Controls the color of the ambient illumination component. The ambient component is included in the lightmap, and is scattered like other light source, and is hence the perfect place to add any HDRI light. The HDRI light can be based on environment and occlusion maps.
overall_color	The diffuse component and both scattering components are multiplied by this color value to produce the final scattering-effect color. This can be used in several ways, among them: To brighten or darken the effect overall. To tint the final result. To connect maps that attenuate light. For example, dirt on an object's surface would block most of the scattered light.
diffuse_color	Defines the color of the diffuse illumination component. This is normally driven by the object's main surface texture.
diffuse_weight	Controls the weight of the diffuse illumination component when it is blended with the other components (ambient, scattering, etc.).
front_sss_color	Controls the color for the front surface scattering. The front surface is the side of the object facing the camera, and so front surface scattering is most visible when that side is well lit.
front_sss_weight	Controls the weight of the front scattering surface when it is blended with the other lighting components (back scattering, diffuse, etc.).
front_sss_radius	Controls the distance that light scatters along the front surface. This value is measured in scene units, but is divided by the scale value on the Advanced Settings tab.
back_sss_color	Controls the color for the back surface scattering (the light going through the object). The Back surface is the side facing away from the camera. Back scattering is most visible when the object is backlit to some extent, or when light passes directly through the object.
back_sss_weight	Controls the weight of the back scattering when it is blended with the other lighting components (front scattering, diffuse, etc.).
back_sss_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.
back_sss_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 when backlit. Generally speaking, higher depth values require an increased number of lightmap samples in order to remove speckling in the rendered image. Normally, the back scattering depth should be set to the same value as the back scattering radius parameter.

s (specular)

specular	Defines the Specular surface color in the illuminated area of the object. The value is blended with the object's Diffuse and Ambient values.
exponent	Defines the rate at which the specularity decays outward.

a (advanced)

lightmap_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.
indirect	When on, includes any indirect lighting (photons, final gathering, etc) in the lightmap to be scattered. This takes additional render time and you should decide on a case-by-case basis if the indirect light is significant enough that seeing it scattered or not makes justifies the extra rendering time.
scale_conversion	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.
scatter_bias	When set to 0 (zero) the scattering is completely uniform. Positive values favor forward scattering, and negative values favor back scattering. The allowed range is -1.0 to 1.0, but the useful range is much smaller. A value of 0.1 (a slight favoring of forward scattering) is a good start.
falloff	Sets the shape of the distance falloff along the scatter radius. Higher values yield a sharper falloff, and lower values a smoother falloff, but also make the perceived scatter distance shorter. For high values (1.0 to 10.0), almost all samples within the scatter radius are weighted equally. For low values (0.1 to 1.0), the samples near the edge of the scatter radius are weighted less.
screen_composit	When enabled, screen compositing is used. When adding together the contribution of many layers of light, it is very easy to quickly blow out and overexpose into white, but the human eye is inherently nonlinear and perceives intensities in a different way. This option allows you to use what is known in many compositing applications as a screen transfer mode between the layers, which yields a softer, more pleasing result. When disabled, normal addition is used. If rendering in a high dynamic range, and a proper tone-operator is applied in the final output stage already compressing the final luminance, it is best to disable this option. If not, enable it for a more pleasing result.

mode	The mode selector for the light list. For more information, see Setting the Light List Mode [Direct Illumination].

Lights

Creates a light list to specifiy which lights should produce the effect. For more information, see Using Light Lists [Direct Illumination].