ABSTRACT
CHAPTER 4 INTRODUCES THE CONCEPTS OF transfer-function design and implementation. Recall that the transfer function is the mechanism used in volume rendering to transform raw data values into the optical properties needed to make a picture. Although the transfer function essentially plays the role of a simple color map, it is one of the most important stages of the volume-rendering pipeline, especially when we are using volume rendering to visualize medical or scientific data. Because the transfer function is responsible for making features of interest in the data visible as well as hiding unimportant regions, the quality of transfer-function specification will have a dramatic impact on the quality of the visualization.
This chapter explores techniques for generalizing transfer-function design. In Chapter 4, the transfer function was defined as a mapping from a single scalar data value to color and opacity. In contrast, this chapter discusses the utility and design of multidimensional transfer functions. By multidimensional, we mean that the input to the transfer function consists of multiple data values, or a vector of values, which are used to determine the optical properties for rendering.
