Browsing by Author "Chuang, JH"

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A geometry-based error estimation for cross-ratios
(2002-01-01)
Liu, JS
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Chuang, JH
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資訊工程學系
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Department of Computer Science
For choosing specific cross-ratios as 2D projective coordinates in various computer vision applications, a reasonable error analysis model is usually required. This investigation adopts the assumption of normal distribution for positioning errors of point features in an image to formulate the error variances of cross-ratios. Based on a geometry-based error analysis, a straightforward way of identifying the cross-ratios with minimum error variances is proposed. Simulation results show that the proposed approach. as well as a further simplified alternative, yield much better estimations of minimum error variances in terms of accuracy, cost, and stability compared with some other methods, e.g., the one based on the rule given by Georis et al. (IEEE Trans. Pattern Anal. Mach. Intell. 20 (4) (1998) 366). Some causes of the performance differences in the estimations are explained using a special configuration of point features. (C) 2001 Pattern Recognition Society. Published by Elsevier Science Ltd. All rights reserved.
A novel potential-based path planning of 3-D articulated robots with moving bases
(2004-07-01)
Lin, CC
;
Pan, CC
;
Chuang, JH
;
資訊工程學系
;
Department of Computer Science
This paper proposes a novel path planning algorithm of 3-D articulated robots with moving bases based on a generalized potential field model. The approach computes, similar to that done in electrostatics, repulsive forces and torques between charged objects. A collision-free path can be obtained by locally adjusting the robot configuration to search for minimum potential configurations using these forces and torques. The proposed approach is efficient since these potential gradients are analytically tractable. In order to speedup the computation, a sequential planning strategy is adopted. Simulation results show that the proposed algorithm works well, in terms of collision avoidance and computation efficiency.
A novel potential-based path planning of 3-D articulated robots with moving bases
(2003)
Lin, CC
;
Pan, CC
;
Chuang, JH
;
資訊工程學系
;
Department of Computer Science
This paper proposes a novel path planning algorithm of 3-D articulated robots with moving bases based on a generalized potential field model. The approach computes, similar to that done in electrostatics, repulsive force and torque between charged objects. A collision-free path can be obtained by locally adjusting the robot configuration to search for minimum potential configurations using these force and torque. The proposed approach is efficient since these potential gradients are analytically tractable. In order to speedup the computation, a sequential planning strategy is adopted. Simulation results show that the proposed algorithm works well, in terms of collision avoidance and computation efficiency.
A potential-based approach for shape matching and recognition
(1996-03-01)
Chuang, JH
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
;
Department of Computer Science
This paper presents a novel potential-based approach for recognizing the shape of a two-dimensional (2D) region by identifying the best match from a selected group of shape templates. The proposed model assumes that the border of every 2D region is uniformly charged. An initially small shape template placed inside a shape sample will experience the repulsive force and torque arising from the potential field. A better match in the shape between the template and the sample can be obtained if the template translates and reorients itself to reduce the potential while growing in size. The shape template with the largest final size corresponds to the best match and represents the shape of the given sample. The potential and the associated repulsive force and torque between the polygonal contours are analytically tractable, hence resulting in high computational efficiency of the matching process. The proposed approach is intrinsically invariant under translation, rotation and size changes of the shape sample. Moreover, not only can the matching be carried out directly for shape contours at different viewscales, but the contours can also be unconnected, provided that the template is confined within the shape sample throughout the matching process.
A potential-based generalized cylinder representation
(2004-12-01)
Chuang, JH
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Ahuja, N
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Lin, CC
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Tsai, CH
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Chen, CH
Generalized cylinder (GC) is a class of parametric shapes that is very flexible and capable of modeling many different types of real-world objects, and have subsequently been the focus of considerable research in the vision community. Most of the related works proposed previously have dealt with the recovery of 3D shape description of objects based on the GC representation from one or more 2D image data. Different from the objective of the previous works, in this paper, we will propose a new approach to obtain a GC-based shape description of 3D objects. The proposed approach of deriving the GC axis is a further extension of the potential-based skeletonization approach presented in (IEEE Trans. Pattern Anal. Mach. Intell. 22(11) (2000) 1241). Simulation results demonstrate that the derived GC representation will yield better approximation of object shape than that based on simpler subclasses of GC since there is, in principle, no restriction on the topology of the GC axis and the shape of the cross-sections. (C) 2004 Elsevier Ltd. All rights reserved.
A potential-based path planning of articulated robots with 2-DOF joints
(2005)
Chuang, JH
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Lin, CC
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Kao, JH
;
Hsieh, CT
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資訊工程學系
This paper proposes a potential-based path planning algorithm of articulated robots with 2-DOF joints. The algorithm is an extension of a previous algorithm developed for 3-DOF joints. While 3-DOF joints result in a very straightforward potential minimization algorithm, 2-DOF joints are obviously more practical for active operations. The proposed approach computes repulsive force and torque between charged objects by using generalized potential model. A collision-free path can be obtained by locally adjusting the robot configuration to search for minimum potential configurations using these force and torque. The optimization of path safeness, through the innovative potential minimization algorithm, makes the proposed approach unique. In order to speedup the computation, a sequential planning strategy is adopted. Simulation results show that the proposed algorithm works well compared with the algorithm for 3-DOF joints, in terms of collision avoidance and computation efficiency.
Adaptive polygonization of geometrically constrained surfaces
(1998-01-01)
Chuang, JH
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Hoffmann, CM
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Ko, KM
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Hwang, WC
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資訊工程學系
Many surfaces in geometric and solid modeling, including offsets and blends, are naturally defined from given surfaces subject to geometric constraints. Surfaces that are geometrically constrained can be uniformly defined as the projection of two-dimensional manifolds (2-surfaces) in n-dimensional space, where n>3. This definition can be used for given surfaces that are implicit or parametric. This paper presents a robust, adaptive polygonization algorithm for evaluating and visualizing geometrically constrained surfaces. Let F be the constrained surface, a 2-surface in n-space, and let pi(F) be its projection into the subspace spanned by the first three coordinates. Our polygonization algorithm computes pi(F). The method works directly with the n-space representation, but performs all major computations in 3-space. Techniques for triangulation, polygon decimation, and local refinement are also presented.
Adaptive polygonization of geometrically constrained surfaces
(1998-01-01)
Chuang, JH
;
Hoffmann, CM
;
Ko, KM
;
Hwang, WC
;
資訊工程學系
Many surfaces in geometric and solid modeling, including offsets and blends, are naturally defined from given surfaces subject to geometric constraints. Surfaces that are geometrically constrained can be uniformly defined as the projection of two-dimensional manifolds (2-surfaces) in n-dimensional space, where n>3. This definition can be used for given surfaces that are implicit or parametric. This paper presents a robust, adaptive polygonization algorithm for evaluating and visualizing geometrically constrained surfaces. Let F be the constrained surface, a 2-surface in n-space, and let pi(F) be its projection into the subspace spanned by the first three coordinates. Our polygonization algorithm computes pi(F). The method works directly with the n-space representation, but performs all major computations in 3-space. Techniques for triangulation, polygon decimation, and local refinement are also presented.
An A-trimmed skeleton for modeling the global shape of polygons
(2006-02-01)
Wu, MC
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Chen, JR
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Chuang, JH
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資訊工程學系
;
工業工程與管理學系
A skeleton is a global shape descriptor that aims to characterize the general appearance of an object to facilitate object classification. Various ways for defining the skeleton of a polygon have been proposed in the literature. Yet, in some cases, these previously proposed skeletons may not intuitively resemble the original polygons and cannot be a good shape descriptor. This research proposes a new definition of skeletons for modeling polygons. The proposed skeleton is termed the area-trimmed (A-trimmed) skeleton. In modeling the global shape of polygons, the A-trimmed skeleton performs much better than other skeletons proposed in the literature. The A-trimmed skeleton can be applied in group technology and facilitate tasks such as punched-part design and fixture design.
An analytically tractable potential field model of free space and its application in obstacle avoidance
(1998-10-01)
Chuang, JH
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Ahuja, N
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資訊工程學系
;
Department of Computer Science
An analytically tractable potential field model of free space is presented in this paper. The model assumes that the border of every two-dimensional (2-D) region is uniformly charged. It is shown that the potential and the resulting repulsion (force and torque) between polygonal regions can be calculated in closed form. By using the Newtonian potential function, collision avoidance between object and obstacle thus modeled is guaranteed in a path planning problem. A local planner is developed for finding object paths going through narrow areas of free space where the obstacle avoidance is most important. Simulation results show that not only does individual object configuration of a path obtained with the proposed approach avoid obstacles effectively, the configurations also connect smoothly into a path.
An analytically tractable potential field model of free space and its application in obstacle avoidance
(1998-10-01)
Chuang, JH
;
Ahuja, N
;
資訊工程學系
;
Department of Computer Science
An analytically tractable potential field model of free space is presented in this paper. The model assumes that the border of every two-dimensional (2-D) region is uniformly charged. It is shown that the potential and the resulting repulsion (force and torque) between polygonal regions can be calculated in closed form. By using the Newtonian potential function, collision avoidance between object and obstacle thus modeled is guaranteed in a path planning problem. A local planner is developed for finding object paths going through narrow areas of free space where the obstacle avoidance is most important. Simulation results show that not only does individual object configuration of a path obtained with the proposed approach avoid obstacles effectively, the configurations also connect smoothly into a path.
Automatic chromosome classification using medial axis approximation and band profile similarity
(2006)
Kao, JH
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Chuang, JH
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Wang, TP
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資訊工程學系
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Department of Computer Science
Automated chromosome classification is an essential task in cytogenetics and has been an important pattern recognition problem. Numerous attempts were made in the past to characterize chromosome to perform clinical and cancer cytogenetics research. It is important to determine optimum features and develop feature extraction schemes for chromosome classification. In this paper we propose novel approaches for medial axis determination and profile matching of human chromosome. The medial axis determination plays a critical role for precise and complete extraction of band patterns of chromosomes. The features of the band profile obtained along the axis are then used in the classification process. In particular, the medial axis is obtained by simple cross-section analysis and the classification is accomplished through iterative pairing of band profiles. According to the experimental results, the developed automatic system can efficiently extract band profiles of the chromosomes along their medial axes, and satisfactory chromosome classification results can be obtained.
Automatic classification of block-shaped parts based on their 2D projections
(1999-07-01)
Chuang, JH
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Wang, PH
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Wu, MC
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資訊工程學系
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工業工程與管理學系
This paper presents a classification scheme for 3D block-shaped parts. A part is block-shaped if the contours of its orthographic projections are all rectangles, A block-shaped part is classified based on its partitioned view-contours, which are the result of partitioning the contours of its orthographic projections by visible or invisible projected line;segments. The regions and their adjacency in a partitioned view-contour are first converted to a graph, then to a reference tree, and finally to a vector form, with which a back-propagation neural network classifier can be trained and applied. The proposed back-propagation neural network classifier is in a cascaded structure and has advantages that each network can be limited to a small size and trained independently. Based on the classification results on their partitioned view-contours, parts are grouped into families that can be in one of the three levels of similarity. Extensive empirical tests have been performed; the pros and cons of the approach are also investigated. (C) 1999 Elsevier Science Ltd. All rights reserved.
Boundary control of subdivision surfaces using an open uniform quadratic subdivision scheme
(2003-09-01)
Hwang, WC
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Chuang, JH
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資訊工程學系
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Department of Computer Science
The ability to control boundary behaviors is critical for the subdivision surface to become a useful representation in computer aided geometric design. Previous methods achieve boundary control by extending the boundary vertices of the control mesh, or by applying different subdivision rules to the boundary edges and vertices. This paper presents an open uniform quadratic subdivision scheme derived from the subdivision of open uniform B-spline surfaces. For meshes with 4-sided boundary and corner faces, the cross-tangent along the boundary curves can also be derived. The proposed scheme leads to a straightforward boundary control that enables two subdivision surfaces to be joined with C-0 and C-1-continuity.
Clustering-based hierarchical radiosity for dynamic environments
(1999-11-01)
Lee, WY
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Chuang, JH
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資訊工程學系
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Department of Computer Science
This paper extends hierarchical radiosity and clustering techniques to dynamic environments, in which dynamic manipulations, such as repositioning an object and changing surface attributes, are repeatedly applied. The cluster techniques can be effective in reducing the computational complexity of both initial linking creation and link updating of dynamic manipulations. When the object is repositioned in a dynamic environment, the affected links, both energy and cluster links, can be identified rapidly by means of our proposed new strategy. As,the total net energy of the environment is decreased, we exploit the so-called history links to un-refine the affected patches. An effective progressive refinement strategy is also applied to further avoid the creation of unnecessary links.
Determination of feature correspondences in stereo images using a calibration polygon
(1997-09-01)
Chiu, JM
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Chen, Z
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Chuang, JH
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Chia, TL
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資訊科學與工程研究所
In this paper, we propose a novel approach to solving the vertex/edge correspondence problem for stereo images. Assume an object is placed on a calibration plate (C-plate) and two perspective views of them are given. The C-plate vertex correspondence, determined by cross-ratios, is used to reduce the search space for determining object vertex/edge correspondence. First, the correspondence of object edges lying on the C-plate (called the object base edges) is considered. This is because the subpolygons obtained from the division of the C-plate by the extended line of each of these base edges are viewpoint invariant, i.e. the cross-ratio of each of their vertices in different images will have equal value. Assume that at least one of the base edges is visible in each image. Since a visible object base edge has to be an object boundary edge in an image, only object boundary edges will be considered for the cross-ratios check for the associated subpolygons as well as other geometric constraint checks in determining the object base vertex/edge correspondence. These geometric constraints include (i) the position of the edges along the boundary of object faces, and (ii) the division of the C-plate vertices by the extended lines of these edges. Based on one of the determined corresponding base edge pairs, the correspondence of all other edges can be determined by constraints similar to (i). Finally, some additional viewpoint invariant measures about the object faces and the C-plates are introduced to resolve the ambiguity problem which may arise for specific viewpoints and some special object shapes. The proposed approach only needs 2-D image data and has no constraint on the number of vertices of an object face. Experimental results are presented for some polyhedral as well as curved objects. (C) 1997 Pattern Recognition Society. Published by Elsevier Science Ltd.
Direct energy minimization for super-resolution on nonlinear manifolds
(2006)
Chang, TL
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Liu, TL
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Chuang, JH
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資訊工程學系
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Department of Computer Science
We address the problem of single image super-resolution by exploring the manifold properties. Given a set of low resolution image patches and their corresponding high resolution patches, we assume they respectively reside on two non-linear manifolds that have similar locally-linear structure. This manifold correlation can be realized by a three-layer Markov network that connects performing super-resolution with energy minimization. The main advantage of our approach is that by working directly with the network model, there is no need to actually construct the mappings for the underlying manifolds. To achieve such efficiency, we establish an energy minimization model for the network that directly accounts for the expected property entailed by the manifold assumption. The resulting energy function has two nice properties for super-resolution. First, the function is convex so that the optimization can be efficiently done. Second, it can be shown to be an upper bound of the reconstruction error by our algorithm. Thus, minimizing the energy function automatically guarantees a lower reconstruction error- an important characteristic for promising stable super-resolution results.
Drawing graphs with nonuniform nodes using potential fields
(2004)
Chuang, JH
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Lin, CC
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Yen, HC
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資訊工程學系
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Department of Computer Science
A potential field approach, coupled with force-directed methods, is proposed in this paper for drawing graphs with nonuniform nodes in 2-D and 3-D. In our framework, nonuniform nodes are uniformly or nonuniformly charged, while edges are modelled by springs. Using certain techniques developed in the field of potential-based path planning, we are able to find analytically tractable procedures for computing the repulsive force and torque of a node in the potential field induced by the remaining nodes. Our experimental results suggest this new approach to be promising, as drawings of good quality for a variety of graphs in 2-D and 3-D can be produced efficiently.
Effective meshing and form factor calculation for accurate progressive radiosity
(2004)
Lee, WY
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Chuang, JH
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資訊工程學系
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Department of Computer Science
In this paper two effective methods are proposed to address two inaccuracies, deficient meshing and error-prone form factors, respectively, in the context of progressive radiosity. The first one addresses the meshing problem using an automatic adaptive subdivision that takes the radiosity difference, the radiosity residual, and the visibility information as error estimates. The second method employs a hybrid form-factor evaluation recursively combining an approximation to the analytic point-to-disk form factor and an accurate form factor from a differential area to a convex polygon. Finally, we demonstrate the effectiveness and practicability of the proposed methods by testing with a set of global illumination test scenes to show the experimental results qualitatively and quantitatively.
Efficient generation of isosurfaces in volume rendering
(1995-11-01)
Chuang, JH
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Lee, WC
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交大名義發表
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資訊工程學系
;
National Chiao Tung University
An efficient method for extracting isosurfaces from volume data is proposed. The method utilizes a modified branch-on-need octree to bypass regions of no current interest. In addition, during the generation of triangle meshes neighboring triangles are merged according to certain criteria. Methods are also given to significantly reduce the space required for octrees. The method is more efficient and generates far fewer triangles than the marching cube algorithm. The performance of the proposed method is compared with that of several existing methods.