Fast surface tracking in three-dimensional binary images

In medical 3-dimensional display, an input scene is represented by an array of volume elements (abbreviated as "voxels"), and an object in the scene is specified as a "connected" set of voxels. In such applications, surface tracking is an important, and often time-consuming, precursory step. One of the most efficient surface detection algorithms reported in the literature tracks a specified surface of a 3-dimensional object by visiting each boundary face in the surface twice. In this paper, we present a new definition of discrete objects and boundaries that leads to a modified algorithm, which, on the average, visits only one-third of the boundary faces twice (and the rest once). The algorithm has been implemented in our display software package and is found to achieve a run-time reduction of approximately 35%. This timing includes the computation of surface-normal information which is needed for the realistic rendering of surfaces. Without this computation, the saving would be about 55%.