The Specular material is used for transparent materials such as glass and water (figure 1). Figure 2 shows the parameters for the Specular material in Maya's Attribute Editor.
Figure 1: An object rendered using the Specular material.
Figure 2: The parameters for the Specular material.
The Reflection value determines the strength of reflections visible on the surface. A lower reflection value increases its ability to transmit light through the object volume. Reflection is closely tied with the index of refraction (IOR) and the two parameters are used together to tune the reflectivity of the specular material.
The Transmission parameter controls how light passes through a transparent surface. It is closely tied with the Index of Refraction to control the transparency of a surface. It accepts a color or texture input. A value of 1 means that light passes through the surface. To create a mirror surface set Transmission to 0 and Index of Refraction to 0. To create colored glass change the color input to something other than white. Transmission should not be confused with opacity; opacity controls the visibility of the surface while transmission controls the transparency. Use Transmission to create a reflective glass surface and use opacity to create the look of a hole in the surface.
Index of Refraction is a value that describes the change in the speed of light as it passes through a medium. As photons of light move through a surface such as water they are slowed causing them to change direction. This shift in direction is visible as the familiar distortion of objects on the other side of the water’s surface. The index of refraction (IOR)of a vacuum is 1, the IOR of water is 1.33 meaning that light travels 1.33 times faster through a vacuum than it does through water. The IOR of most transparent surfaces can be found through an internet search. Knowing the correct IOR of a surface is key to successfully replicating the look of the surface when rendering with Octane.
Film width simulates the look of a thin film of material on the surface. This is useful when you want to create an effect such as the rainbow colors that appear on the surface of an oil slick. Larger values increase the strength of the effect.
The Film IOR controls the Index of Refraction of the thin film, use this option to adjust the colors visible in the film.
The Bump parameter is used to create fine details on the material’s surface using a procedural or image texture. Typically a gray-scale texture is connected to this parameter, light areas of the texture give the appearance of protruding bumps, dark areas create the appearance of indentation. The strength of the bump map can be adjusted by setting the Power or Gamma values on the Octane image texture node. These attributes are covered in more detail under the Texture Overview category.
The Normal parameter is also used to create the look of fine detail on the surface. A normal map is a special type of image texture that uses red, green, and blue color values to perturb the normals of the surface at render time thus giving the appearance of added detail. They can be more accurate than bump maps but require specific software, such as ZBrush, Mudbox, Substance designer, Xnormal, or others to generate.
The Displacement parameter adjusts the height of the vertices of a surface at render time using a texture map. Displacement maps differs from Bump or Normal maps in that the geometry is altered by the texture as opposed to just creating the appearance of detail. Displacement mapping is more computationally expensive than using a bump or normal map but the results can be more realistic especially along the silhouette of the surface. Displacement mapping is covered in more detail under the Texture Overview category.
The Opacity parameter determines which parts of the surface are visible in the render. Dark values indicate transparent areas, light values determine opaque areas. Values in between light and dark create the look of semi transparent areas. You can lower the opacity value to fade the overall visibility of an object or use a texture map to vary the opacity across the surface. For example if you wanted to make a simple polygon plane look like a leaf you would connect a black and white image of the leaf’s silhouette to the opacity channel of the diffuse shader.
The Smooth parameter is a Boolean (meaning that it is a toggle that turns the feature on or off) which smooths the transition between surface normals. If this option is disabled the edges between the polygons of the surface will be sharp giving the surface a faceted look.
The Rounded Edges parameter bevels the edges of the surface at render time automatically without the need to alter or subdivide the geometry. Using this option can enhance the realism of objects by eliminating overly sharp edges. The value refers to the radius of the rounded edge. Higher values for this setting produce rounder edges.
The Roughness parameter simulates the effect of microfacets in the surface which will blur both the reflections on the surface as well as the blurring of the transparency of the surface. For example, one way to create the look of translucent plastic is to make a surface that has a high transmission value as well as a roughness value above zero. Roughness accepts a color value or texture (procedural or image). Typically you’ll want to use gray-scale. Hue information will not have an effect on the roughness.
Increasing the Dispersion value increases the amount of coloration and dispersion in the object’s transmission and in caustics.
OctaneRender for Maya has three types of mediums: absorption, scattering, and volume, which can be used to create translucent surfaces. To use these options the medium input of the Diffuse material needs to be connected to either the Absorption or Scattering medium nodes.
- Absorption Medium produces the appearance of a material that absorbs light while passing through a surface. The color resulting from this absorption depends on the distance light travels through the material. The Absorption map type is covered in more detail under the Texture Overview category.
- Scattering Medium similar to the absorption medium but with an additional option that can be used to simulate subsurface scattering. Subsurface scattering is the phenomena that gives human skin, and similar organic surfaces, their characteristic “glow” under certain lighting conditions. It is a major component in creating the look of realistic skin. The Scattering map type is covered in more detail under the Texture Overview category.
- Volume Medium creates the effect of volumetric surfaces when applied to VDB files imported into Maya using openVDB.
Fake Shadows is a Boolean value that activates architectural glass option for all meshes sharing that material. When enabled, the specular material exhibits the characteristics of Architectural glass with its transparent feature allowing light to illuminate enclosed spaces or frame an exterior view.
This is an option to have refraction affect the alpha channel. This parameter will only have an effect if the alpha channel is enabled in the Render settings’ Kernel parameters.