f i In this paper we present a method for speeding the process of volume rendering a sequence o mages. Speedup is based on exploiting coherency between consecutive images to shorten the n path rays take through the volume. This is achieved by providing each ray with information eeded to leap over the empty space and commence volume traversal at the vicinity of mean- - b ingful data. The algorithm starts by projecting the volume into a C-buffer (Coordinates uffer) which stores, at each pixel location, the object-space coordinates of the first non-empty s t voxel visible from that pixel. For each change in the viewing parameters, the C-buffer i ransformed accordingly. In the case of rotation the transformed C-buffer goes through a pro- - b cess of eliminating coordinates that possibly became hidden. The remaining values in the C uffer serve as an estimate of the point where the new rays should start their volume traverc sal. This space-leaping method can be combined with existing accele...

In this paper we present a fast visualization technique for volumetric data, which is based on a recent nonphotorealistic rendering technique. Our new approach enables alternative insights into 3D data sets (compared to traditional approaches such as direct volume rendering or iso-surface rendering). Object contours, which usually are characterized by locally high gradient values, are visualized regardless of their density values. Cumbersome tuning of transfer functions, as usually needed for setting up DVR views is avoided. Instead, a small number of parameters is available to adjust the non-photorealistic display. Based on the magnitude of local gradient information as well as on the angle between viewing direction and gradient vector, data values are mapped to visual properties (color, opacity), which then are combined to form the rendered image (MIP is proposed as the default compositing stragtegy here). Due to the fast implementation of this alternative rendering approach, it is possible to interactively investigate the 3D data, and quickly learn about internal structures. Several further extensions of our new approach, such as level lines are also presented in this paper. Key words: interactive volume rendering, non-photorealistic rendering, shear-warp projection. 1.

Figure 1: Volumes rendered using 3D textures on commodity GPU. The rendering is accelerated by our empty space skipping. The images are identical to those rendered without the acceleration, while the rendering is about 2 to 5 times faster. We propose methods to accelerate texture-based volume rendering by skipping invisible voxels. We partition the volume into sub-volumes, each containing voxels with similar properties. Subvolumes composed of only voxels mapped to empty by the transfer function are skipped. To render the adaptively partitioned subvolumes in visibility order, we reorganize them into an orthogonal BSP tree. We also present an algorithm that computes incrementally the intersection of the volume with the slicing planes, which avoids the overhead of the intersection and texture coordinates computation introduced by the partitioning. Rendering with empty space skipping is 2 to 5 times faster than without it. To skip occluded voxels, we introduce the concept of orthogonal opacity map, that simplifies the transformation between the volume coordinates and the opacity map coordinates, which is intensively used for occlusion detection. The map is updated efficiently by the GPU. The sub-volumes are then culled and clipped against the opacity map. We also present a method that adaptively adjusts the optimal number of the opacity map updates. With occlusion clipping, about 60 % of non-empty voxels can be skipped and an additional 80% speedup on average is gained for iso-surface-like rendering.

. Tomographic devices often produce data with directionally and spatially dependent resolution. Resampling to cubic voxels is possible at the cost of a significant increase of data volume and rendering time. We present an algorithm for direct ray tracing of rectilinear grids, which enables the implementation of surface rendering with subvoxelsurface detection basedon local interpolation, as well as different volume rendering techniques (color compositing, reprojection, maximum intensity projection). Further we present a faster version of the basic algorithm, based on cubic macro-regions assigned to each background voxel. Each macro-region is defined by its chessboard distance to the nearest foreground voxel and can be skipped during the scene traversal. The speed-up is thus gained by increasing the step along the ray, maintaining 6-connectivity of the ray in the object vicinity, which is necessary for correct surface detection. 1 Volume visualization by ray tracing Ray tra...

Cell-based first-hit ray casting, a new technique for fast perspective volume visualization, is presented in this paper. This technique, based on the well known ray casting algorithm, performs iso-surfacing and supports interactive threshold adjustment. It is accelerated by the reduction of average ray path lengths to only a few steps per pixel. The volume is divided into cubic sub volumes. Each sub volume that is intersected by an iso-surface is projected to the image plane. A local ray casting step within the sub volume is performed for each pixel covered by the projection. Cell-based first-hit ray casting is perfectly suited whenever fast perspective iso-surfacing is required.

This paper presents a fast maximum intensity projection technique based on binary shear-warp factorization. The proposed method divides the density domain into a small number of intervals, and to each interval a binary code representation is assigned. In a preprocessing step, an additional volume is created which contains for each voxel the code of the interval enclosing the given voxel density. We present an appropriate data structure for storing this volume and an efficient lookup table technique which can be used to rapidly access a voxel of a certain density code. The volume is efficiently resampled along viewing rays only in voxels where the densities reside in the interval which contains the appropriate maximum value. Keywords: Maximum Intensity Projection, Volume Rendering, Shear-Warp Factorization. 1 INTRODUCTION Maximum Intensity Projection (MIP) is a widely accepted volume rendering technique which can be used especially for the visualization of location, shape, and topolo...

We present a volume rendering system that is capable of generating high-quality images of large volumetric data (e.g., 512³) in real time (30 frames or more per second). The system is particularly suitable for applications that generate densely occluded scenes of large data sets, such as virtual colonoscopy. The central idea is to divide the volume into sets of axis-aligned slabs. The union of the slabs approximates the shape of a colon. We render sub-volumes enclosed by the slabs and blend the slab images. We use the slab structure to accelerate volume rendering in various aspects. First, empty voxels outside the slabs are skipped. Second, fast view-volume clipping and occlusion culling are applied based on the slabs. Third, slab images are reused for nearby viewpoints. In addition, the slabs can be created very efficiently and they can be used to approximate perspective rendering with parallel projection, so that our system can benefit from fast parallel projection hardware and algorithms. We use image-warping to reduce the artifacts due to the approximation.

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.

The task of real time rendering of today's volumetric datasets is still being tackled by several research groups. A quick calculation of the amount of computation required for real-time rendering of a high resolution volume puts us in the teraflop range. Yet, the demand to support such rendering capabilities is increasing due to emerging technologies such as virtual surgery simulation and rapid prototyping. There are five main approaches to overcoming this seemingly insurmountable performance barrier: (i) data reduction by means of model extraction or data simplification, (ii) realization of special-purpose volume rendering engines, (iii) software-based algorithm optimization and acceleration, (iv) implementation on general purpose parallel architectures, and (v) use of contemporary of-the-shelf graphics hardware. In this presentation we first describe the vision of real-time high-resolution volume rendering and estimate the computing power it demands. We survey the state-of-the art in...

Abstract. This paper proposes a new parallel ray-casting scheme for very large volume data on distributed-memory architectures. Our method, based on data compression, attempts to enhance the speedup of parallel rendering by quickly reconstructing data from local memory rather than expensively fetching them from remote memory spaces. Furthermore, it takes the advantages of both object-order and image-order traversal algorithms: It exploits object-space and image-space coherence, respectively, by traversing a min-max octree block-wise and using a runtime quadtree which is maintained dynamically against pixels ' opacity values. Our compression-based parallel volume rendering scheme minimizes communications between processing elements during rendering, hence is also very appropriate for more practical distributed systems, such as clusters of PCs and/or workstations, in which data communications between processors are regarded as quite costly. We report experimental results on a Cray T3E for the Visible Man dataset. 1