OctaneRender supports participating media inside objects (absorption, SubSurface Scattering, and Volume). These settings are stored in medium nodes, which are attached to the corresponding input pin of Diffuse or Specular material nodes.
There are three types of medium nodes, absorption, scattering and volume.
- Scattering has parameters for absorption, scattering of light passing through the medium, and emission inside the medium.
- Absorption is a simple version with only absorption parameters.
- Volumes are described in more detail in the Effects Overview section. Volume mediums are used on volumetric surfaces such as smoke and clouds and require a VDB file to create the volume objects. VDB files are not supported natively by Maya but can be imported using the OpenVDB tools. More information on this is available at http://www.openvdb.org/.
To render using medium nodes, the Path Tracing or PMC render kernels are the best choice. It is possible to render mediums using Direct Light kernel but only if the medium node is connected to Diffuse material and if Diffuse mode is set to GI.
The Medium nodes are found in the Octane Medium in the Octane section of Hypershade’ Create Node section (Figure 1). These nodes are connected to the Diffuse or Specular materials using their respective Medium slot.
Figure 1: Medium nodes are found in the Octane section of the Hypershade’s Create node window.
Medium nodes should only be added to materials applied to meshes that define a closed volume. A single sided plane will not work. For example a plane representing a leaf will not work properly if a material with a medium is applied to it. The one exception is a plane representing the ground. Octane will treat the ground plane as an infinitely deep surface.
Using Medium Nodes with Octane Materials
Specular materials are the best choice when using a Medium node. Set the Transmission, and Reflection parameters to a non-zero value, or a color other than black, or a texture map. (Figure 2).
Figure 2 : A Medium node is connected to an Octane Specular material. Reflection and Transmission parameters are set above zero.
When connecting a Medium node to a Diffuse material, set the Transmission to a non-zero value, or a color other than black, or a texture map.
When using a Specular shader, the value of the reflection parameter should be set to a low value because only the part of the spectrum that is not reflected can enter the object for scattering. If the reflection is set to 1.0, all light gets reflected regardless of the transmission value. If reflection is set to 0.0, all light gets transmitted through the surface, however, the result is an unnatural appearance. Reflection values of 0.1–0.2 are a good starting point.
If the reflection parameter uses a color, the light transmitted through the surface will be shaded as the complementary color (e.g. if the reflection is set to yellow, the transmitted light is bluish see Figure 3).
Figure 3 : A diagram shows that “complementary” colors are opposite each other on the color wheel.