The ScatteringDefines how fast light gets scattered when traveling through the medium. medium node is used to create the look of subsurface scattering. This is the phenomena where light rays enter a surface, are scattered within the material of surface, and then exit again. It is the key to creating the look of realistic human skin and other organic surfaces. In the figure 1, the absorption color is being strongly scattered with an Octane Float Texture set to 100 to give the look of a waxy or skin-like surface.
Figure 1: The Scattering medium attributes, which include an AbsorptionDefines how fast light is absorbed while passing through a medium. attribute similar to the Absorption medium
Absorption - By default, the absorption attribute is controlled by a value slide ranging from 0 - 1 where 0 is no absorption and 1 is full absorption. A color or texture can be added to replace the value slider. The color's value and saturation can be used to further determine the absorption amount. Note: If the Invert Absorption attribute is active, these values will be behave in the opposite fashion, for example: 0 will be full absorption and 1 will be no absorption.
Invert Absorption - Inverts the absorption characteristics so that the absorption color specified is the same color seen in the surface. For example: Red results in red, otherwise, red would result in green (if this check box is inactive).
Scattering - Determines how quickly light scatters as it moves through the surface. High values mean that light scatters sooner as it enters the surface, and low values mean that light passes deeper into the surface before it scatters. By default, the scattering attribute is controlled by a value slide ranging from 0 - 1 where 0 is no scattering and 1 is full scattering. A color or texture can be added to replace the value slider. The color's value and saturation can be used to further determine the scatter amount.
Phase - Controls the light's direction as it scatters in the surface. A value of 0 results in light scattering equally in all directions. Positive values result in forward scattering, where the photons continue in the same direction they were going when they entered the surface. Negative values result in backwards scattering, where the light moves through the surface in the direction opposite to the angle that the light entered the surface.
Emission - Accepts Octane Blackbody or Texture emission nodes.
Scale - Determines the density of the particles in the surface. The larger the scale value, the more likely light will be absorbed when passing through the surface.
Volume Step Length - The default value is 4, but if the volume is smaller than this, you need to decrease the value. Decreasing this value decreases render speed, and increasing the value causes the ray marching algorithm to take longer steps. If this value exceeds the volume's dimensions, then the ray marching algorithm takes a single step through the whole volume. To get the most accurate results, keep this value as small as possible.
Use Shadow Ray Step Length - Check box for using the Volume Step Length for the Volume Shadow Ray Step Length as well.
Volume Shadow Ray Step Length - Step length that is used by the shadow ray for marching through volumes.
Sample Position DisplacementThe process of utilizing a 2D texture map to generate 3D surface relief. As opposed to bump and normal mapping, Displacement mapping does not only provide the illusion of depth but it effectively displaces the actual geometric position of points over the textured surface. - Allows a texture to control a volume's sample positions displacement.
Volume Step Length - Applicable when rendering Volume mediums. The default value is 4, but if the volume is smaller than this, you need to decrease the value. Decreasing this value decreases render speed, and increasing the value causes the ray marching algorithm to take longer steps. If Volume Step Length exceeds the volume's dimensions, then the ray marching algorithm takes a single step through the whole volume. To get the most accurate results, keep Volume Step Length as small as possible.
Single Scatter Amount - Determines how often direct light is calculated in volumes, as a ratio of scatter events.