A Volume Visualization Algorithm using a coherent Extended Weight Matrix

Direct cell-to-cell volume visualization algorithms, also called projective rendering methods, present the advantage of allowing semi-transparencies and, additionally, as they project all the samples, they avoid the voxel-space aliasing. However, they are generally computationally expensive and artifacts may appear in the projection. In this paper, different projective strategies are reviewed and compared. A new algorithm, based on a back-to-front (BTF) voxel-to-voxel traversal, is proposed. It consists of the computation, in a preprocess, of 16 Extended Generalized Weight (EGW) matrices, based on the voxel's geometry and the viewpoint direction. Taking into advantage the voxel-to-voxel coherence, the EGW are applied incrementally to each voxel as footprints to be composited with the image buffer, according to the voxel shade and opacity values. It is shown that the method avoids artifacts, and that it has a low computational cost because it does not require re-voxellization and it does not perform any geometric computation in the projection process. It is specially suitable for voxel representations and image space resolutions such that the projection of a single voxel covers more than one pixel.