CHAPTER 4 INTRODUCES THE CONCEPTS OF transfer-function designand 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.