Advances in direct volume rendering for visualizing large 3D data sets from scientific and medical applications

Volume rendering permits the visualization of 3D structures without a prior segmentation process. Direct volume rendering is a key technology for visualizing large 3D data sets from scientific or medical applications. This technology employs the use of transfer functions to assign optical properties, such as color, opacity and shading, to original values of the data set being visualized. Thus, a transfer function is particular important to the quality of direct volume-rendered images. However, finding appropriate transfer functions is a tedious task, often done by trial and error. To alleviate these difficulties, efforts to assist in creating transfer functions and improve the efficiency of data exploration are being undertaken. This paper presents and discusses: (1) typical 3D scientific and medical data sets used for direct volume rendering; (2) methods of transfer function design for optimal volume rendering imaging, and (3) generation of automatic and semi-automatic transfer functions for large classes of scalar volume data. The paper also illustrates how direct volume visualization with automatically generated transfer functions, has the potential to significantly reduce the amount of time to segment medical and scientific large data sets as well as enhancing the real-time quality of imaging.