UNC is an Equal Opportunity / Affirmative Action Institution. Abstract Efficient Ray Tracing of Volume Data

Volume rendering is a technique for visualizing sampled scalar functions of three spatial dimen-sions without fitting geometric primitives to the data. Images are generated by computing 2-D pro-jections of a colored semi-transparent volume, where the color and opacity at each point is derived from the data using local operators. Since all voxels participate in the generation of each image, rendering time grows linearly with the size of the dataset. This paper presents a front-to-back image-order volume rendering algorithm and discusses two methods for improving its performance. The first method employs a pyramid of binary volumes to encode coherence present in the data, and the second method uses an opacity threshold to adaptively terminate ray tracing. These methods exhibit a lower complexity than brute-force algorithms, although the actual time saved depends on the data. Examples from two applications are given: medical imaging and molecular graphics. 1