Legacy Bifrost presets are available in the Attribute Editor for standard_volume.

Volume

Density

Density Channel

Interpolation

Displacement

Scatter

Weight

Color

Color Channel

Anisotropy

Anisotropy

Secondary Mix

The anisotropy for the optional secondary Henyey-Greenstein phase function lobe, which is blended linearly with the primary lobe (controlled by the scatter_anisotropy parameter). This allows the phase function to include both forward and back-scattering lobes, which can improve the realism of cloud renderings. 


The cloud on the left (below), using the default anisotropy (0) settings, does not show much forward scattering. The center image shows a strong "silver lining" at the rim of strongly forward scattered light from the sun behind. The cloud on the right adds a secondary phase function lobe which fills in the bulk of the cloud with back-scattered light while maintaining the silver lining.

 

The figure below shows the full parameter space of the dual-phase function model (each cell shows the phase function shape for a given combination of lobe anisotropies, which varies as the lobe mix weight is animated). The blue curves correspond to the old single lobe model.

Secondary Anisotropy

The anisotropy for the optional secondary Henyey-Greenstein phase function lobe, which is blended linearly with the primary lobe (controlled by the scatter_anisotropy parameter). This allows the phase function to include both forward and back-scattering lobes, which can improve realism of cloud renderings.

Anisotropy (primary or secondary) should not exceed about 0.8 at the maximum or be less than -0.8 at the minimum, otherwise, noise and fireflies will appear.

Transparent

Weight

Depth

Channel

Emission

Mode

Scaling

This controls how volume emission is scaled by the properties of the emitting medium.

  • None: no dependence on medium. This is unphysical but included for backward compatibility.
  • Opacity: the emission is based on density and transparency and scaled appropriately to the opacity of the resulting volume. This is physically accurate for blackbody if the scattering color is black.
  • Thermodynamicthis mode is the most physically correct (for blackbody emission) as it also takes into account scattering color, since according to thermodynamics volumes with higher scattering albedo emit less blackbody radiation. For example, burning hydrogen produces steam but barely emits blackbody radiation while sooty smoke readily does.

 

Weight

Color

Channel

Temperature

Temperature

Channel

Blackbody Kelvin

Blackbody Intensity

Blackbody Contrast

The blackbody_contrast parameter (non-physically) reduces the brightness difference between parts of the volume at different temperatures, which can be useful for artistic purposes. This tends to bring out the blackbody colors more vividly (though note that only value 1 is physically correct).