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30th Annual Conference on European Association for computer graphics, EUROgraphics 2009

作者： Ruiters, Roland Klein, Reinhard Institute for Computer Science II University of Bonn Germany

Photo-realistic reproduction of material appearance from images has widespread use in applications ranging from movies over advertising to virtual prototyping. A common approach to this task is to reconstruct the small scale geometry of the sample and to capture the reflectance properties using spatially varying BRDFs. For this, multi-view and photometric stereo reconstruction can be used, both of which are limited regarding the amount of either view or light directions and suffer from either low- or high-frequency artifacts, respectively. In this paper, we propose a new algorithm combining both techniques to recover heightfields and spatially varying BRDFs while at the same time overcoming the above mentioned drawbacks. Our main contribution is a novel objective function which allows for the reconstruction of a heightfield and high quality SVBRDF including view dependent effects. Thereby, our method also avoids both low and high frequency artifacts. Additionally, our algorithm takes interreflections into account allowing for the reconstruction of undisturbed representations of the underlying material. In our experiments, including synthetic and real-world data, we show that our approach is superior to state-of-the-art methods regarding reconstruction error as well as visual impression. Both the reconstructed geometry and the recovered SVBRDF are highly accurate, resulting in a faithful reproduction of the materials characteristic appearance, which is of paramount importance in the context of material rendering. © 2008 The Author(s).

关键词： Reflection

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Example-based interpolation and synthesis of bidirectional texture functions

Example-based interpolation and synthesis of bidirectional t...

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34th Annual Conference on European Association for computer graphics, EUROgraphics 2013

作者： Ruiters, Roland Schwartz, Christopher Kleiny, Reinhard Institute for Computer Science II University of Bonn Germany

Bidirectional Texture Functions (BTF) have proven to be a well-suited representation for the reproduction of measured real-world surface appearance and provide a high degree of realism. We present an approach for designing novel materials by interpolating between several measured BTFs. For this purpose, we transfer concepts from existing texture interpolation methods to the much more complex case of material interpolation. We employ a separation of the BTF into a heightmap and a parallax compensated BTF to cope with problems induced by parallax, masking and shadowing within the material. By working only on the factorized representation of the parallax compensated BTF and the heightmap, it is possible to efficiently perform the material interpolation. By this novel method to mix existing BTFs, we are able to design plausible and realistic intermediate materials for a large range of different opaque material classes. Furthermore, it allows for the synthesis of tileable and seamless BTFs and finally even the generation of gradually changing materials following user specified material distribution maps. © 2013 The Eurographics Association and Blackwell Publishing Ltd.

关键词： Interpolation

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Patch-based texture interpolation

Patch-based texture interpolation

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作者： Ruiters, Roland Schnabel, Ruwen Klein, Reinhard Institute for Computer Science II University of Bonn Germany

In this paper, we present a novel exemplar-based technique for the interpolation between two textures that combines patch-based and statistical approaches. Motivated by the notion of texture as a largely local phenomenon, we warp and blend small image neighborhoods prior to patch-based texture synthesis. In addition, interpolating and enforcing characteristic image statistics faithfully handles high frequency detail. We are able to create both intermediate textures as well as continuous transitions. In contrast to previous techniques computing a global morphing transformation on the entire input exemplar images, our localized and patch-based approach allows us to successfully interpolate between textures with considerable differences in feature topology for which no smooth global warping field exists. © 2010 The Eurographics Association and Blackwell Publishing Ltd.

关键词： Interpolation

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Time-critical collision detection using an average-case approach 03

Time-critical collision detection using an average-case appr...

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2003 ACM Symposium on Virtual Reality Software and Technology, VRST 2003

作者： Klein, Jan Zachmann, Gabriel Heinz Nixdorf Institute Institute of Computer Science University of Paderborn Paderborn Germany Dept. of Computer Graphics and Virtual Reality University of Bonn Bonn Germany

ISBN: (纸本)1581135696

We present a novel, generic framework and algorithm for hierarchical collision detection, which allows an application to balance speed and quality of the collision detection. We pursue an average-case approach that yields a numerical measure of the quality. This can either be specified by the simulation or interaction, or it can help to assess the result of the collision detection in a time-critical system. Conceptually, we consider sets of polygons during traversal and estimate probabilities that there is an intersection among these sets. This can be done efficiently by storing characteristics about the average distribution of the set of polygons with each node in a bounding volume hierarchy (BVH). Consequently, we neither need any polygon intersection tests nor access to any polygons during the collision detection process. Our approach can be applied to virtually any BVH. Therefore, we call a BVH that has been augmented in this way an average-distribution tree or ADB-tree. We have implemented our new approach with two basic BVHs and present performance measurements and comparisons with a very fast previous algorithm, namely the DOPtree. The results show a speedup of about a factor 3 to 6 with only approximately 4% error. Copyright © 2003 ACM.

关键词： Forestry

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Fast and memory efficient view-dependent trimmed NURBS rendering

Fast and memory efficient view-dependent trimmed NURBS rende...

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Pacific Conference on computer graphics and Applications

作者： M. Guthe J. Meseth R. Klein Institute of Computer Science II Computer Graphics University of Bonn Bonn Germany

The problem of rendering large trimmed NURBS models at interactive frame rates is of great interest for industry, since nearly all their models are designed on the basis of this surface type. Most existing approaches first transform the NURBS surfaces into polygonal representation and subsequently build static levels of detail upon them, as current graphics hardware is optimized for rendering triangles. lit this work, we present a method for memory efficient, view-dependent rendering of trimmed NURBS surfaces that yields high-quality results at interactive frame rates. In contrast to existing algorithms, our approach needs not store hierarchies of triangles, since utilizing our special multiresolution seam graph data structure, we are able to generate required triangulations on the fly.

关键词： Spline Surface topography Surface reconstruction Rendering (computer graphics) computer graphics Hardware Solid modeling computer industry Data structures Surface treatment

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Judgment of natural perspective projections in head-mounted display environments 09

Judgment of natural perspective projections in head-mounted ...

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VRST 2009 - 16th ACM Symposium on Virtual Reality Software and Technology

作者： Steinicke, Frank Bruder, Gerd Hinrichs, Klaus Lappe, Markus Kuhl, Scott Willemsen, Pete Visualization and Computer Graphics Research Group Department of Computer Science University of Münster Germany Psychology Department II University of Münster Germany Department of Computer Science Michigan Technological University United States Department of Computer Science University of Minnesota Duluth United States

ISBN: (纸本)9781605588698

The display units integrated in todays head-mounted displays (HMDs) provide only a limited field of view (FOV) to the virtual world. In order to present an undistorted view to the virtual environment (VE), the perspective projection used to render the VE has to be adjusted to the limitations caused by the HMD characteristics. In particular, the geometric field of view (GFOV), which defines the virtual aperture angle used for rendering of the 3D scene, is set up according to the display's field of view. A discrepancy between these two fields of view distorts the geometry of the VE in a way that either minifies or magnifies the imagery displayed to the user. Discrepancies between the geometric and physical FOV causes the imagery to be minified or magnified. This distortion has the potential to negatively or positively affect a user's perception of the virtual space, sense of presence, and performance on visual search tasks. In this paper we analyze if a user is consciously aware of perspective distortions of the VE displayed in the HMD. We introduce a psychophysical calibration method to determine the HMD's actual field of view, which may vary from the nominal values specified by the manufacturer. Furthermore, we conducted an experiment to identify perspective projections for HMDs which are identified as natural by subjects-even if these perspectives deviate from the perspectives that are inherently defined by the display's field of view. We found that subjects evaluate a field of view as natural when it is larger than the actual field of view of the HMD-in some cases up to 50%. Copyright © 2009 by the Association for Computing Machinery, Inc.

关键词： Virtual reality

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Mixed reality based respiratory liver tumor puncture navigation

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Computational Visual Media 2019年第4期5卷 363-374页

作者： Ruotong Li Weixin Si Xiangyun Liao Qiong Wang Reinhard Klein Pheng-Ann Heng Institute of Computer Science II University of Bonn53115 BonnGermany Shenzhen Key Laboratory of Virtual Reality and Human Interaction Technology Shenzhen Institutes of Advanced TechnologyChinese Academy of SciencesChina Department of Computer Science and Engineering Chinese University of Hong KongHong KongChina

This paper presents a novel mixed reality based navigation system for accurate respiratory liver tumor punctures in radiofrequency ablation(RFA).Our system contains an optical see-through head-mounted display device(OST-HMD),Microsoft Holo Lens for perfectly overlaying the virtual information on the patient,and a optical tracking system NDI Polaris for calibrating the surgical utilities in the surgical *** with traditional navigation method with CT,our system aligns the virtual guidance information and real patient and real-timely updates the view of virtual guidance via a position tracking *** addition,to alleviate the difficulty during needle placement induced by respiratory motion,we reconstruct the patientspecific respiratory liver motion through statistical motion model to assist doctors precisely puncture liver *** proposed system has been experimentally validated on vivo pigs with an accurate real-time registration approximately 5-mm mean FRE and TRE,which has the potential to be applied in clinical RFA guidance.

关键词： mixed reality human computer interaction statistical motion model

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New discrepancy measure for evaluation of segmentation quality

New discrepancy measure for evaluation of segmentation quali...

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11th IASTED International Conference on computer graphics and Imaging, CGIM 2010

作者： Smochina, Cristian Manta, Vasile Rogojanu, Radu Department of Computer Science and Engineering Gheorghe Asachi Technical University of Iasi Romania Institute for Computer Graphics and Vision Graz University of Technology Austria

ISBN: (纸本)9780889868243

A new quality measure is proposed for evaluating the performance of segmentation algorithms. This discrepancy method is based on object-by-object comparison of a segmented image (machine segmentation) versus ground-truth segmentation (reference image). The error measure we propose offers two main advantages compared to other quality measures. The first advantage to mention is the use of alternative methods in computing the distance from the contour of the segmented object to the reference one. This method takes into consideration the interior of the object and eliminates the inconveniences that appear in the case of the concave objects. The second improvement comes from adding a weighted shape fitting score: the score of the segmented contour is enhanced by a factor which indicates the similarity between these two curves.

关键词： Image segmentation

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Probabilistic motion sequence generation

Probabilistic motion sequence generation

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computer graphics International

作者： M. Sattler R. Sarlette R. Klein Institute of Computer Science II Computer Graphics University of Bonn Bonn Germany

Creating long animation sequences with nontrivial repetitions is a time consuming and often difficult task. This is true for 2D images and even more true for 3D sequences. Based upon the idea of video textures we propose a simple algorithm to create new user controlled animation sequences based only on a few key frames by the analysis of velocity and position coherence. The simplicity of the method is achieved by carrying out the calculations on the main principal components of the reference animation, hence reducing the dimensionality of the input data. This also leads to significant compression. Smooth animations are ensured, using one of the proposed blending schemes

关键词： Animation Principal component analysis Information geometry Avatars Algorithm design and analysis Humans Reflection Motion control Motion analysis Image sequences

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A distributed object repository for cultural heritage 11

A distributed object repository for cultural heritage

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11th International Symposium on Virtual Reality, Archaeology and Intelligent Cultural Heritage, VAST 2010

作者： Pan, X. Beckmann, P. Havemann, S. Tzompanaki, K. Doerr, M. Fellner, D.W. Institute of Computer Graphics and Knowledge Visualization Graz University of Technology Austria Institute of Computer Science FORTH Crete Greece TU Darmstadt Fraunhofer IGD Germany

ISBN: (纸本)9783905674293

This paper describes the design and the implementation of a distributed object repository that offers cultural heritage experts and practitioners a working platform to access, use, share and modify digital content. The principle of collecting paradata to document each step in a potentially long sequence of processing steps implies a number of design decisions for the data repository, which are described and explained. Furthermore, we provide a description of the concise API our implementation. Our intention is to provide an easy-to-understand recipe that may be valuable also for other data repository implementations that incorporate and operationalize the more theoretical concepts of intellectual transparency, collecting paradata, and compatibility to semantic networks. © The Eurographics Association 2010.

关键词： Semantics

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