In this tutorial, we will cover how to radically change the appearance of a volume using the VolumeSampleRGB shader to produce a thick, 'oily', smokey looking volume. This shader along with the 'Volume Sample Float' shader have 'post-production' style attributes such as 'contrast' and 'gamma'. These attributes are very useful for 'fine tuning' the appearance of a volume. In this example, the VolumeSampleRGB shader has been used to convert a typical fire volume into something that looks more like thick smoke. We will use a default fire simulation from the Pyro FX shelf in Houdini that has been written to disk as a volume VDB.
Below are some other examples of changing the Volume Sample RGB shader's attributes:
Increasing the volume ray depth can also have a dramatic affect on the appearance of the volume. Remember to increase the number of Volume Samples to compensate for any resulting noise. In this example, 6 Volume Samples was used.
When increasing the Volume Ray Depth, you may need to reduce the exposure of the scene lighting to compensate for the additional multiple scattering of illumination in the volume.