The Specular material creates transparent dielectric materials like glass and water (figure 1). When light hits a surface, it is either reflected or absorbed or refracted, but light changes its behavior when it transitions from one medium (for example air) into another medium (for example glass), it reduces speed, and changes direction.


Specular Material

Figure 1: The OctaneRender® Specular material


Specular Material Parameters

Reflection - Determines surface reflection strength. Lower values increase the ability to transmit light through the object volume. Reflection and Index Of Refraction work close together to tune specular material reflectivity.

Transmission - Controls how light passes through a transparent surface. Transmission and Index Of Refraction work close together to control surface transparency, and Transmission accepts color or texture input. A value of 1 lets light pass through the surface, making it transparent. To create a mirror surface, set this parameter to a black color, and set Index Of Refraction to 0. To create colored glass, change the color to something other than white or black. 

BRDF Model- The BRDF (Bidirectional Reflectance Distribution Function) determines the amount of light that a material reflects when light falls on it. For Specular materials, you can choose from five BRDF models. Specific geometric properties (the micro-facet distribution) of the surface affects each BRDF, which describes the surface's microscopic shape (i.e. micro-facet normals) and scales the brightness of the BRDF's reflections. More details can be found in the BRDF Models topic. 


BRDF Models

Figure 2: The three BRDF Models applicable to Specular materials


Retro-Reflective - Activates an optical property where the surface reflects incoming light rays directly back to the original light source. Examples are street signs and safety gear. 

Roughness

Roughness - Simulates the micro-facets effect in the surface, which blurs surface reflections and surface transparency. To create a translucent plastic look, you make a surface with a white or light-colored Transmission color and a Roughness value greater than 0. This parameter accepts a color value or texture (Procedural or Image) - you'll want to use an alpha image or value. Hue information won't affect Roughness.

Anisotropy - Controls the material's reflectance uniformity. Reflectance changes based on surface orientation, or if the rotation is Anisotropic. If the reflectance is uniform in all directions and doesn't change based on the surface's orientation or rotation, then it is Isotropic. This parameter's default value is 0, which sets the Metallic material as Isotropic. Non-zero values mean the material exhibits Anisotropic reflectance, where -1 is horizontal and 1 is vertical.


Anisotropic Roughness

Figure 3: Anisotropic roughness exemplified in materials like brushed metal

 

Rotation - The rotation of the anisotropic Specular reflection channel.

Spread - Determines the tail spread of the specular BSDF.

IOR

Index Of Refraction - Describes the change in the speed of light as it passes through a medium. As light photons move through surfaces like water, they slow down and change direction. This change appears as the object distorting on the other side of the water's surface. A vacuum's Index Of Refraction (IOR) is 1, and water's IOR is 1.33, meaning light travels 1.33 times faster through a vacuum than water. Most transparent surfaces' IOR is accessible on the internet. Knowing a surface's correct IOR is important for replicating a surface's look in OctaneRender®.

Allow Caustics - If enabled, the photon tracing kernel will create caustics for light reflecting or transmitting through the object.

Thin Film Layer

Film Width - Simulates the look of thin film material on a surface, like creating a rainbow color effect that appears on an oil slick's surface. Larger values increase the effect's strength.

Film IOR- Controls the film's IOR by adjusting its visible colors.

Transmission Properties

Dispersion Coefficient - Increasing this value increases the coloration amount and dispersion in the object's transmission and in caustics.

Dispersion Mode - Determines how the IOR and dispersion coefficients are interpreted. 

  • Abbe Number - Measures a transparent material's dispersion. A higher value indicating less dispersion and clearer color perception. 
  • Cauchy Formula - Calculates the refractive index of an optical material at any specific wavelength within the visible spectrum. 

Medium- OctaneRender® has three types of mediums to create translucent surfaces:

  • Absorption Medium - Produces the appearance of a material that absorbs light while passing through a surface. The resulting color depends on the distance that light travels through the material.
  • Random Walk - A newer variant of subsurface scattering that utilizes a stochastic or random process for the scattering of light through an object. This provides the most realistic result when rendering scatter volumes.
  • Scattering Medium - Similar to the Absorption medium, but with an additional option for simulating subsurface scattering. Subsurface scattering is the phenomena that gives human skin and similar organic surfaces their characteristic glow under certain lighting conditions. It's a major component for creating the look of realistic skin.
  • Standard Volume - This provides volume medium options with comprehensive controls for adjusting volume, scatter, transparency, emission, and temperature parameters based on imported VBD grid data. It is not meant to be used as a medium for materials, instead it is typically used with an imported VDB file.
  • Volume Medium - Designed to add color and other volumetric qualities to transmissive objects. This node works best with VDB files but can also be connected to material medium inputs.

Opacity - Determines what surface parts are visible in the render. Dark values indicate transparent areas, and light values indicate opaque areas. Values between light and dark indicate semi-transparent areas. Lowering the Opacity value fades the object's overall visibility, or a Texture map can be used to vary the surface's opacity.  When using an Image texture map, set the Data type to Alpha Image if the image has an Alpha Channel, or Grayscale image for black-and-white images, to load an image for setting transparency. Use the image's Invert checkbox to invert the transparency regions.

Fake Shadows - Activates the Architectural glass option for all meshes sharing that material. When enabled, Specular materials exhibit Architectural glass characteristics with its transparent feature, allowing light to illuminate enclosed spaces or frame an exterior view.

Affect Alpha - This option lets refractions affect the Alpha Channel, as long as you enable the Alpha Channel in the Kernel settings.

Thin wall - When enabled, the geometry becomes very thin, so the ray bounce exits the material immediately, rather than entering the medium.

Geometry Properties

Bump - Creates fine details on the material’s surface using a Procedural or Image texture. Often a Greyscale image texture connects to this parameter - light areas of the texture indicate protruding bumps, and dark areas indicate indentation. You can adjust the Bump map's strength by adjusting the Power or Gamma values on the Image texture node. These attributes are covered in more detail in the Texture topic in this manual.

Bump Height - Determines the height represented by a normalized value of 1.0 in the bump texture. A vaule of 0 disables the bump map and a negative value will invert the bump map. 

Normal - Creates 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 surface normals at render time, 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. To load a full-color Normal map, set the Normal channel to the RGB Image data type. Note that Normal maps take precedence over Bump maps, so you cannot use a Normal map and a Bump map at the same time.

Displacement - Adjusts the height of a surface's vertices at render time using a texture map. Displacement maps differ 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 complex than using a Bump or Normal map, but the results are more realistic, especially along a surface's silhouette. Displacement works with the texture nodes, and the displaced mesh must have UV Texture coordinates. Procedural texture nodes, such as Turbulence or Marble, need to be converted using the Baking Texture node. For more information, see the Displacement topic in this manual.

Smooth - Smooths out the transition between surface normals by blending the polygon edges together. If this option is disabled, the edges between the polygons of the surface appear sharp, giving the surface a faceted look.

Smooth Shadow Terminator - If enabled, self-intersecting shadows are smoothed according to the polygon's curvature.

Round Edges - Rounds the geometry edges by using a shading effect instead of creating additional geometry. See the Round Edges topic in this manual for more information.

Priority - Used to resolve the ambiguity in overlapping surfaces, the surface priority control allows artists to control the order of preference for surfaces. A higher number suggests a higher priority for the surface material, which means it is preferred over a lower priority surface material if a ray enters a higher priority surface and then intersects a lower priority surface while inside the higher priority surface medium.

Custom AOV - Writes a mask to the specified custom AOV.

Custom AOV Channel - Determines whether the custom AOV is written to a specific color channel (R, G, or B) or to all the color channels.

Material Layer - Adds a Material Layer above the base material. See the Material Layers topic in this manual for more details.