Ray-Based Data Level Comparisons of Direct Volume Rendering Algorithms

We present a new method for comparing direct volume rendering (DVR) algorithms. The motivations for this work are: the prevalence of DVR algorithms that produce slightly different images from the same data set and viewing parameters, and the limitations of existing image level comparison methods. In this paper, we describe and demonstrate the effectiveness of several ray-based metrics for data level comparison of direct volume rendering (DVR) algorithms. Unlike other papers on DVR, the focus of this paper is not on speed ups from approximations or implementations with parallel or specialized hardware, but rather on methods for comparison. However, unlike image level comparisons, where the starting point is 2D images, the main distinction of data level comparison is the use of intermediate 3D information to produce the individual pixel values during the rendering process. In addition to identifying the location and extent of differences in DVR images, these data level comparisons allow us to explain why these differences arise from different DVR algorithms. Because of the rich variety of DVR algorithms, finding a common framework for developing data level comparison metrics is one of the main challenges and contribution of this paper. In this paper, we report on how ray tracing can be used as a common framework for comparing a class of DVR algorithms.