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Interpolation – This parameter specifies how emission/scattering/absorption values are computed from the channel.

None – No interpolation, the fastest method, but also prone to artifacts.
Linear – Linear interpolation, good quality, and reasonable speed.
Quadratic – Quadratic interpolation, the best result but the lowest speed.

Step size – Determines ray marching step size. Increasing the value leads to faster rendering with more noise and possibly some artifacts while lowering the value leads to less noise but slower render times.

Flip frame – Flips the frame of the OpenVDB channels (more specifically, the Y and Z axes).

Alpha mode – Specifies how the object is visible in the alpha channel. Available modes are:

Default – This is the default mode. In this mode, the object's alpha value is derived from the data in the OpenVDB file.
Always black – In this mode, the object's alpha value is black (the object shows as transparent).
Always white – In this mode, the object's alpha value is white (the object shows as opaque).

Motion blur & frame interpolation

Mode – Defines how motion blur and frame interpolation are computed.

Disabled – Both frame interpolation and motion blur are disabled (in both cases, we only use the frame closest to the current time).
Simple – Simple linear interpolation between two OpenVDB frames, may lead to artifacts.

Velocity – Enables smooth interpolation/motion blur using velocities stored in the OpenVDB file. For this mode to work properly, you must select a velocity channel.

Multiplier – Specifies the strength of the motion blur effect.

Enable – Enables emissions in the volume.

Channel – Selects the channel that is used as a source for medium emission. Along with channels (grids) presented in the OpenVDB file, such as Temperature, Density, Velocity, etc., a special option can be selected:

Constant – Contains only the value 1, which fills the whole bounding box of the volume grid.

Enable tint – Enables modulation of the emission's final color.

Tint – Selects a solid color different than white to affect the emission's final color.

Shader – Loads a texture map or shader to affect the emission's final color.

Mode – Defines the way in which data in the selected emission channel is mapped to the final emission of the volume.

Blackbody – The emission channel is treated temperature of Kelvin and converted to color according to blackbody radiation laws.
Raw data – Channel data are not mapped and are only influenced by scale and tint.
Channel mapping – The emission channel undergoes mapping to colors, which are accessible under the Channel color mapping section.

Scale – This parameter uniformly scales emission amount after mapping.

Temp. scale – If the emission mode is set to Blackbody, the selected emission channel is treated as the temperature in Kelvin degrees, and these parameters are used to linearly scale the temperature.

Channel color mapping

Channel color mapping can be used to colorize the properties of the volume grid (emission, absorption, scattering) based on a gradient. For example, a red-yellow gradient can be used to create realistic fire.

The channel mapping parameters allow for mapping floating point values stored in the channel to colors. The mapping is computed as follows:

Input scale – The float values are scaled by this parameter so they fit into the [0,1] value range.

Auto-scale – This button allows the computation of the input scaling value automatically.