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Illustrative White Matter Fiber Bundles

COMPUTER GRAPHICS FORUM 2010年第3期29卷 1013-1022页

作者： Otten, Ron Vilanova, Anna van de Wetering, Huub Eindhoven Univ Technol Dept Biomed Engn NL-5600 MB Eindhoven Netherlands Eindhoven Univ Technol Dept Math & Comp Sci NL-5600 MB Eindhoven Netherlands

Diffusion Tensor Imaging (DTI) has made feasible the visualization of the fibrous structure of the brain white matter. In the last decades, several fiber-tracking methods have been developed to reconstruct the fiber tracts from DTI data. Usually these fiber tracts are shown individually based on some selection criteria like region of interest. However, if the white matter as a whole is being visualized clutter is generated by directly rendering the individual fiber tracts. Often users are actually interested in fiber bundles, anatomically meaningful entities that abstract from the fibers they contain. Several clustering techniques have been developed that try to group the fiber tracts in fiber bundles. However, even if clustering succeeds, the complex nature of white matter still makes it difficult to investigate. In this paper, we propose the use of illustration techniques to ease the exploration of white matter clusters. We create a technique to visualize an individual cluster as a whole. The amount of fibers visualized for the cluster is reduced to just a few hint lines, and silhouette and contours are used to improve the definition of the cluster borders. Multiple clusters can be easily visualized by a combination of the single cluster visualizations. Focus+context concepts are used to extend the multiple-cluster renderings. Exploded views ease the exploration of the focus cluster while keeping the context clusters in an abstract form. Real-time results are achieved by the GPU implementation of the presented techniques.

关键词： I.3.3 [Computer Graphics]: Picture/Image Generation—Bitmap and framebuffer operations Display algorithms viewing algorithms

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ADR - Anatomy-Driven Reformation

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IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS 2014年第12期20卷 2496-2505页

作者： Kretschmer, Jan Soza, Grzegorz Tietjen, Christian Suehling, Michael Preim, Bernhard Stamminger, Marc FAU Erlangen Dept Comp Graph Forchheim Germany Siemens Healthcare Comp Tomog Forchheim Germany Univ Magdeburg Dept Simulat & Graph D-39106 Magdeburg Germany

Dedicated visualization methods are among the most important tools of modern computer-aided medical applications. Reformation methods such as Multiplanar Reformation or Curved Planar Reformation have evolved as useful tools that facilitate diagnostic and therapeutic work. In this paper, we present a novel approach that can be seen as a generalization of Multiplanar Reformation to curved surfaces. The main concept is to generate reformatted medical volumes driven by the individual anatomical geometry of a specific patient. This process generates flat views of anatomical structures that facilitate many tasks such as diagnosis, navigation and annotation. Our reformation framework is based on a non-linear as-rigid-as-possible volumetric deformation scheme that uses generic triangular surface meshes as input. To manage inevitable distortions during reformation, we introduce importance maps which allow controlling the error distribution and improving the overall visual quality in areas of elevated interest. Our method seamlessly integrates with well-established concepts such as the slice-based inspection of medical datasets and we believe it can improve the overall efficiency of many medical workflows. To demonstrate this, we additionally present an integrated visualization system and discuss several use cases that substantiate its benefits.

关键词： Medical Visualization Volume Reformation viewing algorithms

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Interactive level-of-detail selection using image-based quality metric for large volume visualization

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IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS 2007年第1期13卷 122-134页

作者： Wang, Chaoli Garcia, Antonio Shen, Han-Wei Ohio State Univ Dept Comp Sci & Engn Columbus OH 43210 USA Intel Corp Bellevue WA 98007 USA

For large volume visualization, an image-based quality metric is difficult to incorporate for level-of-detail selection and rendering without sacrificing the interactivity. This is because it is usually time-consuming to update view-dependent information as well as to adjust to transfer function changes. In this paper, we introduce an image-based level-of-detail selection algorithm for interactive visualization of large volumetric data. The design of our quality metric is based on an efficient way to evaluate the contribution of multiresolution data blocks to the final image. To ensure real-time update of the quality metric and interactive level-of-detail decisions, we propose a summary table scheme in response to runtime transfer function changes and a GPU-based solution for visibility estimation. Experimental results on large scientific and medical data sets demonstrate the effectiveness and efficiency of our algorithm.

关键词： data compaction and compression perceptual reasoning viewing algorithms interaction techniques hierarchical image representation volume visualization

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Novel-View Synthesis of Outdoor Sport Events Using an Adaptive View-Dependent Geometry

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COMPUTER GRAPHICS FORUM 2012年第2期31卷 325-333页

作者： Germann, Marcel Popa, Tiberiu Keiser, Richard Ziegler, Remo Gross, Markus Swiss Fed Inst Technol Zurich Switzerland

We propose a novel fully automatic method for novel-viewpoint synthesis. Our method robustly handles multi-camera setups featuring wide-baselines in an uncontrolled environment. In a first step, robust and sparse point correspondences are found based on an extension of the Daisy features [TLF10]. These correspondences together with back-projection errors are used to drive a novel adaptive coarse to fine reconstruction method, allowing to approximate detailed geometry while avoiding an extreme triangle count. To render the scene from arbitrary viewpoints we use a view-dependent blending of color information in combination with a view-dependent geometry morph. The view-dependent geometry compensates for misalignments caused by calibration errors. We demonstrate that our method works well under arbitrary lighting conditions with as little as two cameras featuring wide-baselines. The footage taken from real sports broadcast events contains fine geometric structures, which result in nice novel-viewpoint renderings despite of the low resolution in the images.

关键词： 1.3.3 [Computer Graphics]: Picture/Image Generation&mdash viewing algorithms

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Large volume visualization of compressed time-dependent datasets on GPU clusters

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PARALLEL COMPUTING 2005年第2期31卷 205-219页

作者： Strengert, M Magallón, M Weiskopf, D Guthe, S Ertl, T Univ Stuttgart Inst Visualizat & Interact Syst D-70569 Stuttgart Germany Univ Costa Rica Escuela Fis San Pedro 2060 Costa Rica Univ Tubingen GRIS WSI D-72076 Tubingen Germany

We describe a system for the texture-based direct volume visualization of large data sets on a PC cluster equipped with GPUs. The data is partitioned into volume bricks in object space, and the intermediate images are combined to a final picture in a sort-last approach. Hierarchical wavelet compression is applied to increase the effective size of volumes that can be handled. An adaptive rendering mechanism takes into account the viewing parameters and the properties of the data set to adjust the texture resolution and number of slices. We discuss the specific issues of this adaptive and hierarchical approach in the context of a distributed memory architecture and present corresponding solutions. Furthermore, our compositing scheme takes into account the footprints of volume bricks to minimize the costs for reading from framebuffer, network communication, and blending. A detailed performance analysis is provided for several network, CPU, and GPU architectures-and scaling characteristics of the parallel system are discussed. For example, our tests on a eight-node AMD64 cluster with InfiniBand show a rendering speed of 6 frames per second for a 2048 x 1024 x 1878 data set on a 1024(2) viewport. (c) 2005 Elsevier B.V. All rights reserved.

关键词： graphics systems distributed/network graphics viewing algorithms

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Interactive view-dependent rendering over networks

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IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS 2008年第3期14卷 576-589页

作者： Zheng, Zhi Prakash, Edmond Chan, Tony K. Y. Nanyang Technol Univ Singapore Singapore Microsoft Corp Redmond WA 98052 USA Manchester Metropolitan Univ Manchester M1 5GD Lancs England

For a client-server-based view-dependent rendering system, the overhead of view-dependent rendering and the network latency are major obstacles in achieving interactivity. In this paper, we first present a multiresolution hierarchy traversal management strategy to control the overhead of view-dependent rendering for low-capacity clients. Then, we propose a predictive parallel strategy to overcome the network latency for client-server-based view-dependent multiresolution rendering systems. Our solution is to make the client process and the server process run in parallel using the rendering time to cover the network latency. For networks with long round-trip times, we manage to overlap the network latency for one frame with the rendering time for multiple frames. View parameter prediction is incorporated to make the parallelism of the client and the server feasible. In order to maintain an acceptable view-dependent rendering quality in the network environment, we develop a synchronization mechanism and a dynamic adjustment mechanism to handle the transient network slowdowns and the changes in the network condition. Our experimental results, in comparison with the sequential method, show that our predictive parallel approach can achieve an interactive frame rate while keeping an acceptable rendering quality for large triangle models over networks with relatively long round-trip times.

关键词： display algorithms viewing algorithms graphics systems distributed/network graphics

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Unstructured Light Fields

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COMPUTER GRAPHICS FORUM 2012年第2期31卷 305-314页

作者： Davis, Abe Levoy, Marc Durand, Fredo Stanford Univ Stanford CA 94305 USA

We present a system for interactively acquiring and rendering light fields using a hand-held commodity camera. The main challenge we address is assisting a user in achieving good coverage of the 4D domain despite the challenges of hand-held acquisition. We define coverage by bounding reprojection error between viewpoints, which accounts for all 4 dimensions of the light field. We use this criterion together with a recent Simultaneous Localization and Mapping technique to compute a coverage map on the space of viewpoints. We provide users with real-time feedback and direct them toward under-sampled parts of the light field. Our system is lightweight and has allowed us to capture hundreds of light fields. We further present a new rendering algorithm that is tailored to the unstructured yet dense data we capture. Our method can achieve piecewise-bicubic reconstruction using a triangulation of the captured viewpoints and subdivision rules applied to reconstruction weights.

关键词： Computer Graphics [1.3.3]: Picture/Image Generation&mdash Digitizing and Scanning viewing algorithms

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Panoramic Video from Unstructured Camera Arrays

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COMPUTER GRAPHICS FORUM 2015年第2期34卷 57-68页

作者： Perazzi, F. Sorkine-Hornung, A. Zimmer, H. Kaufmann, P. Wang, O. Watson, S. Gross, M. ETH Zurich Switzerland Disney Res Zurich Switzerland Walt Disney Imagineering Glendale CA USA

We describe an algorithm for generating panoramic video from unstructured camera arrays. Artifact-free panorama stitching is impeded by parallax between input views. Common strategies such as multi-level blending or minimum energy seams produce seamless results on quasi-static input. However, on video input these approaches introduce noticeable visual artifacts due to lack of global temporal and spatial coherence. In this paper we extend the basic concept of local warping for parallax removal. Firstly, we introduce an error measure with increased sensitivity to stitching artifacts in regions with pronounced structure. Using this measure, our method efficiently finds an optimal ordering of pair-wise warps for robust stitching with minimal parallax artifacts. Weighted extrapolation of warps in non-overlap regions ensures temporal stability, while at the same time avoiding visual discontinuities around transitions between views. Remaining global deformation introduced by the warps is spread over the entire panorama domain using constrained relaxation, while staying as close as possible to the original input views. In combination, these contributions form the first system for spatiotemporally stable panoramic video stitching from unstructured camera array input.

关键词： Categories and Subject Descriptors (according to ACM CCS) I.3.3 [Computer Graphics]: Picture/Image Generation&mdash viewing algorithms

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Occlusion Culling in OpenSG PLUS

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COMPUTERS & GRAPHICS-UK 2004年第1期28卷 87-92页

作者： Staneker, D Bartz, D Strasser, W Univ Tubingen Wilhelm Schickard Inst Informat D-72076 Tubingen Germany Univ Tubingen WSI GRIS Visual Comp Med Grp D-72076 Tubingen Germany

Very large polygonal models are frequently used in scientific computing, mechanical engineering, or virtual medicine. An effective technique to handle these large models is occlusion culling. Like most large model techniques, occlusion culling trades overhead costs with the rendering costs of the possibly occluded geometry. In this paper, we present occlusion culling techniques for OpenSG. These techniques utilize OpenGL or OpenGL extensions to determine occlusion information. Techniques utilizing image-space and temporal coherence are used to optimize occlusion query efficiency. Only the standard OpenSG data structures are used and no precomputation is necessary for the presented techniques. (C) 2003 Elsevier Ltd. All rights reserved.

关键词： scene graph occlusion culling visibility viewing algorithms graphics packages

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Guided Procedural Modeling

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COMPUTER GRAPHICS FORUM 2011年第2期30卷 325-334页

作者： Benes, B. St'ava, O. Mech, R. Miller, G. Purdue Univ W Lafayette IN 47907 USA Adobe Inc San Jose CA USA

Procedural methods present one of the most powerful techniques for authoring a vast variety of computer graphics models. However, their massive applicability is hindered by the lack of control and a low predictability of the results. In the classical procedural modeling pipeline, the user usually defines a set of rules, executes the procedural system, and by examining the results attempts to infer what should be changed in the system definition in order to achieve the desired output. We present guided procedural modeling, a new approach that allows a high level of top-down control by breaking the system into smaller building blocks that communicate. In our work we generalize the concept of the environment. The user creates a set of guides. Each guide defines a region in which a specific procedural model operates. These guides are connected by a set of links that serve for message passing between the procedural models attached to each guide. The entire model consists of a set of guides with procedural models, a graph representing their connection, and the method in which the guides interact. The modeling process is performed by modifying each of the described elements. The user can control the high-level description by editing the guides or manipulate the low-level description by changing the procedural rules. Changing the connectivity allows the user to create new complex forms in an easy and intuitive way. We show several examples of procedural structures, including an ornamental pattern, a street layout, a bridge, and a model of trees. We also demonstrate interactive examples for quick and intuitive editing using physics-based mass-spring system.

关键词： I.3.3 [Computer Graphics]: Picture/Image Generation viewing algorithms

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