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Item Image-Based Rendering of Surfaces from Volume Data(The Eurographics Association, 2001) Chen, Baoquan; Kaufman, Arie; Tang, Qingyu; K. Mueller and A. KaufmanWe present an image-based rendering technique to accelerate rendering of surfaces from volume data. We cache the fully volume rendered image (called keyview) and use it to generate novel views without ray-casting every pixel. This is achieved by first constructing an underlying surface model of the volume and then texture mapping the keyview onto the geometry.When the novel view moves slightly away from the keyview, most of the original visible regions in the keyview are still visible in the novel view. Therefore, we only need to cast rays for pixels in the newly visible regions, which usually occupy only a small portion of the whole image, resulting in a substantial speedup. We have applied our technique to a virtual colonoscopy system and have obtained an interactive navigation speed through a 512<sup>3</sup> size patient colon. Our experiments demonstrate an average of an order of magnitude speedup over that of traditional volume rendering, compromising very little on image quality.Item Accelerating Voxel-Based Terrain Rendering with Keyframe-Free Image-Based Rendering(The Eurographics Association, 2001) Qin, Jiafa; MingWan,; Qu, Huamin; Kaufman, Arie; K. Mueller and A. KaufmanWe propose a voxel-based terrain rendering method which incorporates a novel keyframe-free image-based rendering algorithm and a new heuristic ray coherence raycasting algorithm. The current image is generated by warping the previous image with a revised 3D warping algorithm and filling holes by raycasting, accelerated by ray coherence and multiresolution ray traversal. This method not only achieves good performance, but also allows arbitrary viewing directions. We further accelerate the rendering with multiprocessor parallelism and have achieved a real-time rendering rate of 30Hz on a 16-processor SGI Power Challenge.Item OpenVL - The Open Volume Library(The Eurographics Association, 2003) Lakare, Sarang; Kaufman, Arie; I. Fujishiro and K. Mueller and A. KaufmanOpenVL is a modular, extensible, and high performance library for handling volumetric datasets. It provides a standard, uniform, and easy to use API for accessing volumetric data. It allows the volumetric data to be laid out in different ways to optimize memory usage and speed. It supports reading/writing of volumetric data from/to files in different formats using plugins. It provides a framework for implementing various algorithms as plugins that can be easily incorporated into user applications. The plugins are implemented as shared libraries which can be dynamically loaded as needed. OpenVL is developed openly and is a free software available on the web.Item Multiresolution Volume Simplification and Polygonization(The Eurographics Association, 2003) Zhang, Nan; Kaufman, Arie; I. Fujishiro and K. Mueller and A. KaufmanWe propose a multiresolution volume simplification and polygonization algorithm. Traditionally, voxel-based algorithms lack the adaptive resolution support and consequently simplified volumes quickly lose sharp features after several levels of downsampling, while tetrahedral-based simplification algorithms usually generate poorly shaped triangles. In our method, each boundary cell is represented by a carefully selected representative vertex. The quadric error metrics are applied as the geometric error metric. Our approach first builds an error pyramid by bottom-up cell merging. We avoid topology problems in hierarchical cell merging by disabling erroneous cells and penalizing cells containing disconnected surface components with additional costs. Then, a top-down traversal is used to collect cells within a user specified error threshold. The surfacenets algorithm is used to polygonize these cells. We enhance it with online triangle shape optimization and budget control. Finally, we discuss a novel octree implementation which greatly eases the polygonization operations.Item GPU-based Object-Order Ray-Casting for Large Datasets(The Eurographics Association, 2005) Hong, Wei; Qiu, Feng; Kaufman, Arie; Klaus Mueller and Thomas Ertl and Eduard GroellerWe propose a GPU-based object-order ray-casting algorithm for the rendering of large volumetric datasets, such as the Visible Human CT datasets. A volumetric dataset is decomposed into small sub-volumes, which are then organized using a min-max octree structure. The small sub-volumes are stored in the leaf nodes of the min-max octree, which are also called cells. The cells are classified using a transfer function, and the visible cells are then loaded into the video memory or the AGP memory. The cells are sorted and projected onto the image plane front to back. The cell projection is implemented using a volumetric ray-casting algorithm on the GPU. In order to make the cell projection more efficient, we devise a propagation method to sort cells into layers. The cells within the same layer are projected at the same time. We demonstrate the efficiency of our algorithm using the Visible Human datasets and a segmented photographic brain dataset on commodity PCs.Item GPU-Accelerated Volume Splatting With Elliptical RBFs(The Eurographics Association, 2006) Neophytou, Neophytos; Mueller, Klaus; McDonnell, Kevin T.; Hong, Wei; Guan, Xin; Qin, Hong; Kaufman, Arie; Beatriz Sousa Santos and Thomas Ertl and Ken JoyRadial Basis Functions (RBFs) have become a popular rendering primitive, both in surface and in volume rendering. This paper focuses on volume visualization, giving rise to 3D kernels. RBFs are especially convenient for the representation of scattered and irregularly distributed point samples, where the RBF kernel is used as a blending function for the space in between samples. Common representations employ radially symmetric RBFs, and various techniques have been introduced to render these, also with efficient implementations on programmable graphics hardware (GPUs). In this paper, we extend the existing work to more generalized, ellipsoidal RBF kernels, for the rendering of scattered volume data. We devise a post-shaded kernel-centric rendering approach, specifically designed to run efficiently on GPUs, and we demonstrate our renderer using datasets from subdivision volumes and computational science.Item Multi-dimensional Reduction and Transfer Function Design using Parallel Coordinates(The Eurographics Association, 2010) Zhao, Xin; Kaufman, Arie; Ruediger Westermann and Gordon KindlmannMulti-dimensional transfer functions are widely used to provide appropriate data classification for direct volume rendering. Nevertheless, the design of a multi-dimensional transfer function is a complicated task. In this paper, we propose to use parallel coordinates, a powerful tool to visualize high-dimensional geometry and analyze multivariate data, for multi-dimensional transfer function design. This approach has two major advantages: (1) Combining the information of spatial space (voxel position) and parameter space; (2) Selecting appropriate highdimensional parameters to obtain sophisticated data classification. Although parallel coordinates offers simple interface for the user to design the high-dimensional transfer function, some extra work such as sorting the coordinates is inevitable. Therefore, we use a local linear embedding technique for dimension reduction to reduce the burdensome calculations in the high dimensional parameter space and to represent the transfer function concisely. With the aid of parallel coordinates, we propose some novel high-dimensional transfer function widgets for better visualization results. We demonstrate the capability of our parallel coordinates based transfer function (PCbTF) design method for direct volume rendering using CT and MRI datasets.Item Real-Time Volume Rendering for Virtual ColonoscopyS(The Eurographics Association, 2001) Li, Wei; Kaufman, Arie; Kreeger, Kevin; K. Mueller and A. KaufmanWe present a volume rendering system that is capable of generating high-quality images of large volumetric data (e.g., 512<sup>3</sup>) 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.Item Blowing in the Wind(The Eurographics Association, 2003) Wei, Xiaoming; Zhao, Ye; Fan, Zhe; Li, Wei; Yoakum-Stover, Suzanne; Kaufman, Arie; D. Breen and M. LinWe present an approach for simulating the natural dynamics that emerge from the coupling of a flow field to lightweight, mildly deformable objects immersed within it. We model the flow field using a Lattice Boltzmann Model (LBM) extended with a subgrid model and accelerate the computation on commodity graphics hardware to achieve real-time simulations. We demonstrate our approach using soap bubbles and a feather blown by wind fields, yet our approach is general enough to apply to other light-weight objects. The soap bubbles illustrate Fresnel reflection, reveal the dynamics of the unseen flow field in which they travel, and display spherical harmonics in their undulations. The free feather floats and flutters in response to lift and drag forces. Our single bubble simulation allows the user to directly interact with the wind field and thereby influence the dynamics in real time.Item Prostate Cancer Visualization from MR Imagery and MR Spectroscopy(The Eurographics Association and Blackwell Publishing Ltd., 2011) Marino, Joseph; Kaufman, Arie; H. Hauser, H. Pfister, and J. J. van WijkProstate cancer is one of the most prevalent cancers among males, and the use of magnetic resonance imaging (MRI) has been suggested for its detection. A framework is presented for scoring and visualizing various MR data in an efficient and intuitive manner. A classification method is introduced where a cumulative score volume is created which takes into account each of three acquisition types. This score volume is integrated into a volume rendering framework which allows the user to view the prostate gland, the multi-modal score values, and the sur- rounding anatomy. A visibility persistence mode is introduced to automatically avoid full occlusion of a selected score and indicate overlaps. The use of GPU-accelerated multi-modal single-pass ray casting provides an inter- active experience. User driven importance rendering allows the user to gain insight into the data and can assist in localization of the disease and treatment planning. We evaluate our results against pathology and radiologists' determinations.