A technique for rendering images Of volumes containing mixtures of materials is presented. The shading model allows both the interior of a material and the boundary between materials to be colored. Image projection is performed by simulating the absorption of light along the ray path to the eye. The algorithms used are designed to avoid artifacts caused by aliasing and quantization and can be efficiently implemented on an image computer. Images from a variety of applications are shown.

A popular technique for rendition of isosurfaces in sampled data is to consider cells with sample points as corners and approximate the isosurface in each cell by one or more polygons whose vertices are obtained by interpolation of the sample data. That is, each polygon vertex is a point on a cell edge, between two adjacent sample points, where the function is estimated to equal the desired threshold value. The two sample points have values on opposite sides of the threshold, and the interpolated point is called an intersection point. When one cell face has an intersection point ineach of its four edges, then the correct connection among intersection points becomes ambiguous. An incorrect connection can lead to erroneous topology in the rendered surface, and possible discontinuities. We show that disambiguation methods, to be at all accurate, need to consider sample values in the neighborhood outside the cell. This paper studies the problems of disambiguation, reports on some solutions, and presents some statistics on the occurrence of such ambiguities. A natural way to incorporate neighborhood information is through the use of calculated gradients at cell corners. They provide insight into the behavior of a function in well-understood ways. We introduce two gradient-consistency heuristics that use calculated gradients at the corners of ambiguous faces, as well as the function values at those corners, to disambiguate at a reasonable computational cost. These methods give the correct topology on several examples that caused problems for other methods we examined.

this paper, except Figures 4.8 and 4.9, are two dimensional, representing polyhedra as polygons. 1 2 3 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 4 * vp Figure 4.1: Visibility ordering of the cells of a mesh relative to viewpoint vp. can be computed and stored in a preprocessing step. The MPVO algorithm can be extended to order many nonconvex meshes; this is described in detail in Section 4.4.2. 4.3 Preliminary Definitions A convex polyhedron in E

The size of volumetric datasets used in medical environments is increasing at a rapid pace. Due to excessive pre-computation and memory demanding data structures, most current approaches for volume visualization do not meet the requirements of daily clinical routine. In this diploma thesis, an approach for interactive high-quality rendering of large medical data is presented. It is based on image-order raycasting with object-order data traversal, using an optimized cache coherent memory layout. New techniques and parallelization strategies for direct volume rendering of large data on commodity hardware are presented. By using new memory efficient acceleration data structures, high-quality direct volume rendering of several hundred megabyte sized datasets at sub-second frame rates on a commodity notebook is achieved.

In this thesis, we address the problem of large-scale data visualization from two aspects, dimensionality and resolution. We introduce a novel data structure called Differential Time-Histogram Table (DTHT) for visualization of time-varying (4D) scalar data. The proposed data structure takes advantage of the coherence in time-varying datasets and allows efficient updates of data necessary for rendering during data exploration and visualization while guaranteeing that the scalar field visualized is within a given error tolerance of the scalar field sampled. To address the high-resolution datasets, we propose a hierarchical data structure and introduce a novel hybrid framework to improve the quality of multi-resolution visualization. For more accurate rendering at coarser levels of detail, we reduce aliasing artifacts by ap-proximating data distribution with a Gaussian basis at each level of detail and we reduce blurring by using transparent isosurfaces to capture high-frequency features usually missed in coarse resolution renderings.