ABSTRACT
FOR SOLVING THE LIGHT-TRANSFER EQUATIONS from Chapter 1, we need to know the optical properties, such as the emission and absorption coefficients, at each point inside the volume. In the previous chapter, we assumed that we are given these coefficients directly, and we examined different implementations that compute the volume-rendering integral.
In scientific visualization, however, we are given a volumetric data set that contains abstract scalar data values that represent some spatially varying physical property. In general, there is no natural way to obtain emission and absorption coefficients from such data. Instead, the user must decide how the different structures in the data should look by assigning optical properties to the data values using arbitrary mappings. This mapping is called a transfer function. This process of finding an appropriate transfer function is often referred to as classification.
