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Mediums

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 pins of DiffuseAmount of diffusion, or the reflection of light photons at different angles from an uneven or granular surface. Used for dull, non-reflecting materials or mesh emitters., SpecularAmount of specular reflection, or the mirror-like reflection of light photons at the same angle. Used for transparent materials such as glass and water., or Universal material nodes.

There are five primary types of Medium nodes:

• ScatteringDefines how fast light gets scattered when traveling through the medium. - Has parameters for AbsorptionDefines how fast light is absorbed while passing through a medium., Scattering, and Emission.
• Random Walk - A newer variant of subsurface scattering that ensures a more realistic result.
• Absorption - A simple version with just Absorption parameters.
• Schlick Phase Function - An independent node that can be used to control which direction the scattering occurs.
• Standard Volume MediumA shading system designed to render volumes such as smoke and fog. - A comprehensive node with the flexibility to specify what VDBDreamworks’ open-source C++ library housing the data structures and tools implementation for storing and manipulating volume data, like smoke and other amorphous materials. The purpose of OpenVDB is mostly to have an efficient way to store volumetric data in memory and on disk. It has evolved into a more general toolkit that also lets you accomplish other things, such as fracturing volumes, converting meshes to volumes and vice versa. However, it does not include a computational fluid dynamics solver, and therefore it cannot procedurally generate smoke or fire. OpenVDB is fully integrated as a library in OctaneRender. For more information about OpenVDB, please see http://www.openvdb.org/. grid data can be used for the various node channels.

• Volume Medium - Used on volumetric surfaces such as smoke and clouds. It requires a VDB file to create the volume objects. VDB files are not supported natively by Unreal^® Engine, but you can import them as part of an ORBXThe ORBX file format is the best way to transfer scene files from 3D Authoring software programs that use the Octane Plug-in such as Octane for Maya, Octane for Cinema 4D, or OctaneRender Standalone. This format is more efficient than FBX when working with Octane specific data as it provides a flexible, application independent format. ORBX is a container format that includes all animation data, models, textures etc. that is needed to transfer an Octane scene from one application to another.^® package. For more information, visit http://www.openvdb.org/.
• Volume Gradient - Designed to work with a Volume medium. It requires a VDB file to create the volume objects.

To render with Medium nodes, the Path Tracing or PMC render kernels are the best choices. It is possible to render MediumsThe behavior of light inside a surface volume described by scatter, absorption, and transmission characteristics. using the Direct Light kernel, but the results are not as accurate.

The Medium nodes are found in the Medium section of the Octane MaterialThe representation of the surface or volume properties of an object. window. These nodes connect to the Diffuse, Specular, and Universal materials using their respective Medium slots.

Figure 1: A Scattering medium node attached to the Medium pin on an Octane Specular materialUsed for transparent materials such as glass and water.

Add Medium nodes to MaterialsA set of attributes or parameters that describe surface characteristics. 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 if you apply a Medium to a Material. The one exception is a plane representing the ground. OctaneRender^® treats the ground plane as an infinite, deep surface.

Specular materials are the best choice when using a Medium node. Set the TransmissionA surface characteristic that determines if light may pass through a surface volume. and Reflection parameters to a non-zero value, or a color other than black, or a Texture map.

Figure 2: A Medium node connected to a Specular material

When using a Specular shader, you should set the Reflection to a low value because just the part of the spectrum that is not reflected can enter the object for scattering. If you set Reflection to 1.0, all light reflects regardless of the Transmission value. If you set Reflection to 0.0, all light transmits through the surface. However, the result is an unnatural appearance. Reflection values of 0.1 - 0.2 are good starting points.

If the Reflection attribute uses a color, the light transmitted through the surface is shaded as the complementary color. For example, if the reflection is set to yellow, the transmitted light is bluish.

Figure 3 : A diagram shows that complementary colors are opposite each other on the color wheel

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