Automating transfer function design for volume rendering using hierarchical clustering of material boundaries

Transfer function design plays a crucial role in direct volume rendering. Furthermore, it has a major influence on the efficiency of the visualization process. We have developed a framework that facilitates the semi-automatic design of transfer functions. Similarly to other approaches we generate clusters in the transfer function domain. We created a real-time interaction with a hierarchy of clusters. This interaction effectively substitutes cumbersome settings of clustering thresholds. Our framework is also able to easily combine different clustering criteria. We have developed two similarity measures for clustering of material boundaries. One is based on the similarity of the boundaries in the transfer function domain and the other on their spatial relation. We use the LH space as the transfer function domain. This space facilitates the clustering of material boundaries. We demonstrate our approach on several examples.