OpenVDB Workflow

In this tutorial, we will go through how to setup and use the volume_sample_float shader to adjust the color temperature effect of an OpenVDB file.

Note:

A tutorial on how to write volumes to OpenVDB from Houdini can be found here.

Start off by downloading a VDB file such as the explosion.vdb or fire.vbd file, for example, from the OpenVDB download page.
Create an Arnold Volume - Plugins > C4DtoA > Arnold Volume.
Select the .vdb volume in the File path attribute.
Create a Point light and position it outside of the volume.

Standard Volume

Create a standard_volume shader - Arnold > Volume > standard_volume in the Material Manager
Assign the standard_volume shader to the Volume.

We can use a Volume Sample Float shader to control the appearance of the fire volume effect. This shader will remap the values of the 3D voxel grid in the same manner as tone-mapping and remapping filters to an image in Photoshop, which operates in a 2D grid.

Open the shader network editor of the standard_volume shader.
Create a volume_sample_float shader. Connect it to the density parameter of the standard_volume shader.
Set density to the volume_sample_float channel.
Remove density from the standard_volume.density channel.
Set the standard_volume.emission to channel and use density as the Channel. This will give us the fire.

We can use the volume_sample_float shader to alter the appearance of the smoke and fire. The following images show different adjustment attributes and their effect on the volume.

Input Max



₁	₂	₃

Bias



_0.92	_0.95	_0.97

Gain



_0.1	_0.2	_0.3

Output Max



_0.5	_0.6	_0.7