Research and Implement of Multi-Dimensional Transfer Function Based on Boundaries

The transfer function is the basis of direct volume rendering, and how to design it is also a crucial step for the volume visualization. Multi-dimensional transfer functions are a very effective way to extract materials and their boundaries for scalar data. For many applications, boundaries carry most of the relevant information. Based on the definition of transfer functions, this paper discusses the principle of the multidimensional transfer function based on boundaries which uses the scalar values and the gradient magnitudes as the domains, and presents a method of calculation the gradient magnitude, then implements a histogram of the occurrences of the multiple data values. Finally, we present a set of direct manipulation widgets that guide users towards transfer function settings appropriate for their visualization and data exploration interests. The transfer function and widgets combine to form a powerful system for interactive volume exploration.