Data - centric , without data model

alizing large 3D data sets from scientific or medical applications. Transfer functions are particularly important to the quality of direct volume-rendered images. A transfer function assigns optical properties, such as color and opacity, to original values of the data set being visualized. Unfortunately, finding good transfer functions proves difficult. Pat Hanrahan called it one of the top 10 problems in volume visualization in his inspiring keynote address at the 1992 Symposium on Volume Visualization. And it seems that today, almost a decade later, there are still no good solutions at hand. Or are there? In a panel discussion at the Visualization 2000 conference, we pitched four of the currently most promising approaches to transfer function design against each other. The four approaches and their advocates are