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Geometric parameters based cubic PH curve interpolation and approximation

Journal of Information and Computational Science 2009年第6期6卷 2423-2432页

作者： Cheng, Min Wang, Guojin Department of Mathematics Zhejiang University Zhejiang Hangzhou 310000 China College of Science Zhejiang University of Technology Zhejiang Hangzhou 310000 China Institute of Computer Graphics and Image Processing Zhejiang University Zhejiang Hangzhou 310000 China

The Pythagorean-hodograph curves offer unique computational advantages in computer aided design and manufacturing. In this paper, geometric parameters based cubic PH curve interpolation and approximation algorithms are presented. The essential geometric parameters include the ratio ρ of the adjacent control polygon legs, the control polygon angle θ, the first control polygon leg L, the included angle δ between the first control polygon edge and the edge joining the origin O and the first control point, as well as the coefficient Dir of curve rotation. Furthermore the problem of PH curve approximation with endpoints interpolation to a cubic non-PH curve is studied, including the algorithms based on different geometric parameters input {δ, θ}, {ρ, θ} and {ρ, δ} respectively. © 2009 Binary Information Press.

关键词： Approximation algorithms

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Approximate merging of multiple Bézier segments

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Progress in Natural Science:Materials International 2008年第6期18卷 757-762页

作者： Min Chenga,b,Guojin Wanga,* ainstitute of Computer graphics and image processing,Zhejiang University,Hangzhou 310027,China bCollege of Science,Zhejiang University of technology,Hangzhou 310032,China Institute of Computer Graphics and Image Processing Zhejiang University Hangzhou 310027 China College of Science Zhejiang University of Technology Hangzhou 310032 China

This paper deals with the approximate merging problem of multiple adjacent Bézier curves with dierent degrees by a single Bézier curve,which is a frequently seen problem in *** unified matrix representation for precise merging is presented and the approx-imate merging curve is further derived based on matrix *** at the endpoints of curves is also discussed in the merging *** show that the method in this paper achieves satisfying merging results.

关键词： Computer-aided geometric design Bézier curve Approximate merging Matrix representation

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Real-time Facial Features Tracker Based on Topologic Information and Similarity Analysis

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电子学报(英文版) 2008年第2期17卷 205-209页

作者： LIANG Ronghua FANG Jinglong MAO Jianfei ZHOU Delong College of Information Engineering Zhejiang University of Technology Hangzhou 310014 China State Key Laboratory of Audiovisual Information Processing Peking University Beijing 100871 China Institute of Graphics and Image Hangzhou Dianzi Universtity Hangzhou 310018 China

Real-time facial features tracking of video can be widely used in face recognition, video surveillance, face animation and Human-Computer Interaction. We present a fast tracking approach, and our method only requires simple device - a digital camera and a PC, and our approach needs limited user interactions. We first use eigenface and topologic information to detect the position and the size of face from the first frame, and facial features of the first frame are acquired automatically. The successor of the first frame can be tracked by using similarity analysis and motion estimation, the automatic tracker of first frame is also used to resolve the features occlusion problem when the tracked features disappear which is a difficult issue for tracking. Experimental results show that our approach is easily implemented, and the analysis also shows the high robustness of our method.

关键词：拓扑信息相似分析特征跟踪运动评估

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An eLearning activity control model for SCORM's sequencing prerequisites

An eLearning activity control model for SCORM's sequencing p...

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4th International Conference on Semantics, Knowledge, and Grid, SKG 2008

作者： Narae, Park Hyuna, Kim Kwanghoon, Kim Hwajung, Park Junchul, Chun Yeiseon, Hwang Collaboration Technology Research Lab. Contents Convergence Software Research Center KYONGGI UNIVERSITY Korea Republic of Graphics and Image Processing Research Lab. Contents Convergence Software Research Center KYONGGI UNIVERSITY Korea Republic of Gyeonggi Educational Information Research Institute GYEONGGI PROVINCIAL OFFICE OF EDUCATION Korea Republic of

ISBN: (纸本)9780769534015

In this paper1, we propose an eLearning activity control model that is used to efficiently and graphically defining SCORM's content aggregation model and its sequencing prerequisites through a formal approach. In terms of the representation of the eLearning activity sequencing, the SCORM2 content aggregation model uses a XML-based and rule-driven approach, which is called an activity-tree, over a tree-structured content organization. However, it is unwilling to say that the activity-tree approach be an efficient way, because the course developer is required to be complete-understanding about the SCORM's complicated sequencing rerequisites and other extensions. Therefore, the model proposed in this paper aims to realize the concept of process-driven eLearning content aggregating approach. Eventually the proposed model becomes a theoretical basis for implementing a process-driven eLearning aggregation modeling and enactment system satisfying the SCORM's sequencing prerequisite specifications. We strongly believe that the eLearning activity control model and its system deliver a way of much more convenient work in composing SCORM's content aggregation models and in implementing eLearning management system as well. © 2008 IEEE.

关键词： Forestry

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Sparse MRF appearance models for fast anatomical structure localisation

Sparse MRF appearance models for fast anatomical structure l...

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2007 18th British Machine Vision Conference, BMVC 2007

作者： Donner, René Mičušsík, Branislav Langs, Georg Bischof, Horst Institute for Computer Graphics and Vision Graz University of Technology Austria Pattern Recognition and Image Processing Group Vienna University of Technology Austria GALEN Group Laboratoire de Mathématiques Appliquées Aux Systèmes Ecole Centrale de Paris France

ISBN: (纸本)1901725340

image segmentation methods like active shape models, active appearance models or snakes require an initialisation that guarantees a considerable overlap with the object to be segmented. In this paper we present an approach that localises anatomical structures in a global manner by means of Markov Random Fields (MRF). It does not need initialisation, but finds the most plausible match of the query structure in the image. It provides for precise, reliable and fast detection of the structure and can serve as initialisation for more detailed segmentation steps. Sparse MRF Appearance Models (SAMs) encode a priori information about the geometric configurations of interest points, local features at these points and local features along the edges of adjacent points. This information is used to formulate a Markov Random Field and the mapping of the modeled object (e.g. a sequence of vertebrae) to the query image interest points is performed by the MAX-SUM algorithm. The local image information is captured by novel symmetry-based interest points and local descriptors derived from Gradient Vector Flow. Experimental results are reported for two data-sets showing the applicability to complex medical data.

关键词： image segmentation

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Local Structure Detection with Orientation-invariant Radial Configuration

Local Structure Detection with Orientation-invariant Radial ...

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Conference on Computer Vision and Pattern Recognition (CVPR)

作者： Lech Szumilas Rene Donner Georg Langs Allan Hanbury Pattern Recognition and Image Processing Group University of Technology Vienna Vienna Austria Institute for Computer Graphics and Vision Graz University of Technology Graz Austria

Local image descriptors have proved themselves as useful tools for many computer vision tasks such as matching points between multiple images of a scene and object recognition. Current descriptors, such as SIFT, are designed to match image features with unique local neighborhoods. However, the interest point detectors used with SIFT often fail to select perceptible local structures in the image, and the SIFT descriptor does not directly encode the local neighborhood shape. In this paper we propose a symmetry based interest point detector and radial local structure descriptor which consistently captures the majority of basic local image structures and provides a geometrical description of the structure boundaries. This approach concentrates on the extraction of shape properties in image patches, which are an intuitive way to represent local appearance for matching and classification. We explore the specificity and sensitivity of this local descriptor in the context of classification of natural patterns. The implications of the performance comparison with standard approaches like SIFT are discussed.

关键词： Detectors Shape Computer vision Layout Object recognition

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A comparision of Model-based methods for knee cartilage segmentation

A comparision of Model-based methods for knee cartilage segm...

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2nd International Conference on Computer Vision Theory and Applications, VISAPP 2007

作者： Cheong, J. Faggian, N. Langs, G. Suter, D. Cicuttini, F. Dept. of Electrical Dept. of Computer Systems Engineering Monash University Australia Clayton School of Information Technology Monash University Australia Institute for Computer Graphics and Vision Graz University of Technology Austria Pattern Recognition and Image Processing Group Vienna University of Technology Austria Dept. of Epidemiology Dept. of Preventive Medicine Monash University Australia

Osteoarthritis is a chronic and crippling disease affecting an increasing number of people each year. With no known cure, it is expected to reach epidemic proportions in the near future. Accurate segmentation of knee cartilage from magnetic resonance imaging (MRI) scans facilitates the measurement of cartilage volume present in a patient's knee, thus enabling medical clinicians to detect the onset of osteoarthritis and also crucially, to study its effects. This paper compares four model-based segmentation methods popular for medical data segmentation, namely Active Shape Models (ASM) (Cootes et al., 1995), Active Appearance Models (AAM) (Cootes et al., 2001), Patch-based Active Appearance Models (PAAM) (Faggian et al., 2006), and Active Feature Models (AFM) (Langs et al., 2006). A comprehensive analysis of how accurately these methods segment human tibial cartilage is presented. The results obtained were benchmarked against the current "gold standard" (cartilage segmented manually by trained clinicians) and indicate that modeling local texture features around each landmark provides the best results for segmenting human tibial cartilage.

关键词： Medical imaging

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Motion Analysis of Endovascular Stent-Grafts by MDL Based Registration

Motion Analysis of Endovascular Stent-Grafts by MDL Based Re...

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International Conference on Computer Vision (ICCV)

作者： Georg Langs Nikos Paragios Rene Donner Pascal Desgranges Alain Rahmouni Hicham Kobeiter GALEN Group Laboratoire de Mathématiques Appliquées aux Systàmes Ecole Centrale de Paris France Institute for Computer Graphics and Vision Graz University of Technology Austria Pattern Recognition and Image Processing Group University of Technology Vienna Austria University of Paris XII Paris France

The endovascular repair of a traumatic rupture of the thoracic aorta - that would otherwise lead to the death of the patient - is performed by delivering a stent-graft into the vessel at the rupture location. The age range of the affected patients is large and the stent-graft will stay in the body for the remaining life. The technique is relatively new, and no experience with regard to long-term effects, and durability exists. To predict long-term complications, such as ruptures or destructive interactions with surrounding tissue during the life of the patient, it is important to understand the - rather intense and constant - movement of the stent- graft during the cardiac cycle. A computed tomography with heart gating (gated CT) acquires sequences that show the region of the stent-graft at different time points. We analyze the motion of stent-grafts with a model based approach. Stent-grafts are represented as sparse sets of axis points extracted from the gated CT, and motion patterns are captured by a minimum description length based group-wise registration of the stent-graft at different time points. No parameterization or a priori definition of the topology is necessary, and highly variable elasticity properties in the data volume can by accounted for by the sparse statistical model, that captures correlations and motion components of the stent-graft. We report results for deformation models and registration accuracy for 5 patients.

关键词： Motion analysis Computed tomography Biomedical imaging Heart Buildings Computer graphics Pattern recognition image processing Hospitals Data mining

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3D and Infrared Face Reconstruction from RGB data using Canonical Correlation Analysis

3D and Infrared Face Reconstruction from RGB data using Cano...

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International Conference on Pattern Recognition

作者： M. Reiter R. Donner G. Langs H. Bischof Pattern Recognition and Image Processing Group Vienna University of Technology Austria Graz University of Technology Institute for Computer Graphics and Vision Austria

In this paper, we apply a multiple regression method based on canonical correlation analysis (CCA) to face data modelling. CCA is a factor analysis method which exploits the correlation between two high dimensional signals. We first use CCA to perform 3D face reconstruction and in a separate application we predict near-infrared (NIR) face texture. In both cases, the input data are color (RGB) face images. Experiments show, that due to the correlation between input and output signal, only a small number of canonical factors are needed to describe the functional relation of RGB images to the respective output (NIR images and 3D depth maps) with reasonable accuracy

关键词： Shape Face detection Lighting image reconstruction image analysis image databases Pattern analysis Rendering (computer graphics) image color analysis Pattern recognition

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Active Feature Models

Active Feature Models

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International Conference on Pattern Recognition

作者： G. Langs P. Peloschek R. Donner M. Reiter H. Bischof Institute for Computer Graphics and Vision Graz University of Technology Austria Pattern Recognition and Image Processing Group University of Technology Vienna Austria Department of Radiology Medical University of Vienna Austria

ISBN: (纸本)0769525210

In this paper active feature models are proposed. They utilize local texture features and a statistical shape model for the reliable localization of landmarks in images. They are related to active appearance models, but instead of modelling the entire texture of an object they represent image texture by means of local descriptors. The approach has advantages with complex image data like anatomical structures that exhibit high texture variation with limited relevance for the recognition of the object location. Experimental results and the comparison to AAMs on different data sets indicate that active feature models can improve search speed and result accuracy, considerably

关键词： Shape Active appearance model Biomedical imaging image texture image edge detection image texture analysis Computer graphics Pattern recognition image processing Radiology

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