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Mediums

OctaneRender^® supports participating media inside objects. These settings are stored in Medium nodes, which are attached to the corresponding input pin 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., and Universal material nodes.

There are six types of Medium nodes:

• AbsorptionDefines how fast light is absorbed while passing through a medium. - A simple version with just Absorption parameters.
• Random Walk - A newer variant of subsurface scattering that ensures a more realistic result.
• ScatteringDefines how fast light gets scattered when traveling through the medium. - Has parameters for Absorption, Scattering, and Emission.
• Schlick - can be used to control which direction the scattering occurs.
• Volume Ramp Tex - provides precise control for a Volume geometry's color, such as a flame.
• Volume MediumA shading system designed to render volumes such as smoke and fog. - See the Effects Overview section for more details.

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. with the Direct Light kernel, but only if the Medium node is connected to a Diffuse materialUsed for dull, non-reflecting materials or mesh emitters. and if Diffuse Mode is set to GI. You can access the Medium nodes from the Add menu.

Figure 1: Accessing the Medium nodes from the Add menu

There are some things to keep in mind about using Mediums with Meshes and Specular materials:

Meshes

Add Medium nodes to MaterialsA set of attributes or parameters that describe surface characteristics. when you've applied them 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 a MaterialThe representation of the surface or volume properties of an object. with a Medium is applied to it. The one exception is a plane representing the ground: OctaneRender treats the ground plane as an infinitely deep surface.

Specular and Null Materials

Specular materials were the best choice when using a Medium node. When using a Specular materialUsed for transparent materials such as glass and water., set the value of the Reflection parameter to a low value because only the part of the spectrum that is not reflected can enter the object for scattering. If you set Reflection to 1, all light reflects regardless of the TransmissionA surface characteristic that determines if light may pass through a surface volume. value. If Reflection is set to 0, all light transmits through the surface, but the result is an unnatural appearance. Reflection values of 0.1 - 0.2 are good starting points.

However, the Null Material node can now be used for mesh objects that have an invisible surface but contain a medium. This is equivalent to setting up a specular material with IOR 1 and a reflection of 0 and a transmission of 1. However, that methodology no longer makes sense with nested dielectric. The Null Material was created to make a medium with no surface work in all cases.

If the Reflection parameter uses a color, OctaneRender^® shades the light transmitted through the surface as the complementary color. For example, if the reflection is set to yellow, the transmitted light is a bluish color.

Figure 2 : Complementary colors are opposite from each other on the color wheel

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