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Direct Volume Rendering with Shading

via Three-Dimensional Textures

Allen Van Gelder Kwansik Kim

Baskin Center for Computer Engineering and Computer Science

University of California

Santa Cruz, CA 95064 USA



July 19, 1996


A new and easy-to-implement method for direct volume rendering that uses 3D texture maps for acceleration, and incorporates directional lighting, is described. The implementation, called Voltx, produces high-quality images at nearly interactive speeds on workstations with hardware support for three-dimensional texture maps. Previously reported methods did not incorporate a light model, and did not address issues of multiple texture maps for large volumes. Our research shows that these extensions impact performance by about a factor of ten. Voltx supports orthographic, perspective, and stereo views. This paper describes the theory and implementation of this technique, and compares it to the shear-warp factorization approach.

A rectilinear data set is converted into a three-dimensional texture map containing color and opacity information. Quantized normal vectors and a lookup table provide efficiency. A new tesselation of the sphere is described, which serves as the basis for normal-vector quantization. A new gradient-based shading criterion is described, in which the gradient magnitude is interpreted in the context of the field-data value and the material classification parameters, and not in isolation. In the rendering phase, the texture map is applied to a stack of parallel planes, which effectively cut the texture into many slabs. The slabs are composited to form an image.

Keywords: Computer Graphics, Scientific Visualization, Texture Map, Direct Volume Rendering, Spherical Tesselation.

Note: This report appears in Proceedings of ACM/IEEE Symposium on Volume Visualization, San Francisco, Oct., 1996, except for the following modifications. The appendix of this report does not appear in the proceedings. References to the appendices are replaced by references to this report, in the proceedings. The proceedings includes 1/2 page of color images that are not included in the report, as distributed electronically. The color images are available separately from the authors.