Optimal generation of transfer functions for direct volume rendering

Volume rendering implements the visualization of 3D structures without a prior segmentation process. Direct volume rendering is a key imaging technology for visualizing large 3D data sets from scientific or medical applications. Visualization is rendered by transfer functions which assign optical properties such as color, opacity and shading to original values of the data set being visualized. Constructing appropriate transfer functions is a tedious task, generally requiring substantial hand tuning for each new data set and often done by trial and error. This paper introduces a semi-automatic method of transfer function generation which makes volume rendering surfaces more intuitive and less labor intensive. Fundamentally, this method rests on an algorithm that computes the boundary characteristics in a volume and uses this information to guide the user toward opacity function settings which readily display the boundaries.