WSCG '2005: Short Papers
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Item Nailing and Pinning: Adding Constraints to Inverse Kinematics(Václav Skala - UNION Agency, 2005) Greeff, Mardé; Haber, Jörg; Seidel, Hans-Peter; Skala, VáclavInverse kinematics is commonly applied to compute the resulting movement of an avatar for a prescribed target pose. The motion path computed by inverse kinematics, however, often differs from the expected or desired result due to an underconstrained parameter space of the degrees-offreedom of all joints. In such cases, it is necessary to introduce additional constraints, for instance by locking a joint's position and / or rotation. We present a method to fix a joint in terms of position and explain how to incorporate these constraints into the inverse kinematics solution.Item A new formulation of differential radiosity and a rendering application(Václav Skala - UNION Agency, 2005) Arquès, D.; Biri, V.; Derpierre, O.; Skala, VáclavAmong all the existing realistic lighting methods, the radiosity method is the only one that gives precisely an analytic solution of diffuse light exchanges. The gradient of this solution have been studied but not often used in a context of pure rendering. We present in this article a method to render a surface using the radiosity contour levels. First, we define a differential formulation of the radiosity equation which leads us to a new expression of the gradient of radiosity. We deduce from this general equation a simpler equation of this gradient in the case of a planar surface lighted by a light source reduced to a point. Then we present our method to render planar surfaces using a radial mesh that follows the contour levels of the radiosity. This method is shown to improve the quality of the rendering and decrease the number of vertices used for rendering.Item Managing Data Flow in Interactive MR Environments(Václav Skala - UNION Agency, 2005) Dähne, Patrick; Seibert, Helmut; Skala, VáclavIn this paper the concept and design of a software framework which provides a transparent data flow for interactive Mixed Reality (MR) applications is discussed. The design was affected by our demands on platform independency, simplicity, network transparency, maximum performance and availability of runtime debugging facilities. Our software framework tries to simplify the development of MR applications by using the concept of a data flow graph. The developer builds such a graph from a library of small software components that communicate via the edges of the graph.Item Minimization of the mapping error using coordinate descent(Václav Skala - UNION Agency, 2005) Dzemyda, Gintautas; Bernataviciene, Jolita; Kurasova, Olga; Marcinkevicius, Virginijus; Skala, VáclavVisualization harnesses the perceptual capabilities of humans to provide the visual insight into data. Structure preserving projection methods can be used for multidimensional data visualization. The goal of this paper is to suggest and examine the projection error minimization strategies that would allow getting a better and less distorted projection. The classic algorithm for Sammon’s projection and two new its modifications are examined. All the algorithms are oriented to minimize the projection error because even a slight reduction in the projection error changes the distribution of points on a plane essentially. The conclusions are made on the results of experiments on artificial and real data sets.Item Towards reverse design of freeform shapes(Václav Skala - UNION Agency, 2005) Vergeest, Yoris S. M.; Langerak, R.; Song, Y.; Wang, C.; Bronsvoort, W. F.; Nyirenda, P. J.; Skala, VáclavThe need for more intuitive, faster and more effective tools for freeform product design is still an outstanding research issue in shape modeling. We propose a new methodology in which the designer can define optimal shape modification tools for the situation at hand. The key to this method is a dialogue between the designer and the computer, in which the details of the requested shape modifier are settled. The proposed tool, called user-defined modifier (UDM), is based on recent techniques from freeform shape recognition and parameterized, template-controlled shape modification. The dialogue between user and the system is described, and the basic techniques for the UDM tool are presented as well.Item Multi-agent Animation Techniques for Traffic Simulation in Urban Environments(Václav Skala - UNION Agency, 2005) Tang, Wen; Wan, Tao Ruan; Skala, VáclavWe describe an approach of using the multi-agent animation method for traffic simulations. The presented simulation system uses an individual-based agent behaviour model and discrete cell-based roadway configurations. The behaviour model defines the driving characteristics of each vehicle agent in a simulated traffic network, and the cell-based configurations allow real-time dynamic path planning and efficient traffic flow simulations. By incorporating the advantages of discrete cellular automation algorithms and the continuous model of fluid dynamics, our 3D virtual reality traffic simulation system achieves realistic and accurate simulations in virtual environments.Item An Efficient One-Dimensional Fractal Analysis for Iris Recognition(Václav Skala - UNION Agency, 2005) Teo, Chuan Chin; Ewe, Hong Tat; Skala, VáclavAn iris recognition system is proposed in this paper. This system implements (a) the combination of proposed black hole search method and integro-differential operators for iris localization, (b) one-dimensional fractal analysis for feature extraction and (c) dissimilarity operator for matching. The black hole search method achieves 100% accuracy of pupil detection for both CASIA and MMU Iris databases. Experiment results show that the proposed system has an encouraging result with low EER to 4.63% in CASIA iris database and 4.17% in MMU iris database. It provides an alternative solution for iris recognition and acts as a spring board for further investigation.Item Physically-based Simulation of Hair Strips in Real-Time(Václav Skala - UNION Agency, 2005) Taşkiran, Hasan Doğu; Güdükbay, Uğur; Skala, VáclavIn this paper, we present our implementation of physically-based simulation of hair strips. We used a mass-spring model followed by a hybrid approach where particle systems and the method of clustering of hair strands are employed. All the forces related to springs are implemented: gravity, repulsions from collisions (head and ground), absorption (ground only), frictions (ground and air), internal spring frictions. Real-time performance is achieved for physically-based simulation of hair strips and promising results in terms of the realistic hair behavior and hair rendering are obtained.Item Appearance Based Recognition of Complex Objects by Genetic Prototype-Learning(Václav Skala - UNION Agency, 2005) Stommel, Martin; Kuhnert, Klaus-Dieter; Skala, VáclavThis paper describes a method to recognize and classify complex objects in digital images. To this end, a uniform representation of prototypes is introduced. The notion of a prototype describes a set of local features which allow to recognize objects by their appearance. During a training step a genetic algorithm is applied to the prototypes to optimize them with regard to the classification task. After training the prototypes are compactly stored in a decision tree which allows a fast detection of matches between prototypes and images. The proposed method is tested with natural images of highway scenes, which were divided into 15 classes (including one class for rejection). The learning process is documented and the results show a classification rate of up to 93 percent for the training and test samples.Item Skeleton-based temporal segmentation of human activities from video sequences(Václav Skala - UNION Agency, 2005) Quirion, Sébastien; Branzan-Albu, Alexandra; Bergevin, Robert; Skala, VáclavThis paper presents a new multi-step, skeleton-based approach for the temporal segmentation of human activities from video sequences. Several signals are first extracted from a skeleton sequence. These signals are then segmented individually to localize their cyclic segments. Finally, all individual segmentations are merged with respect to the global set of signals. Our approach requires no prior knowledge on human activities and can use any generic stick-model. Two different techniques for signal segmentation and for the fusion of the individual segmentations are proposed and tested on a database of fifteen video sequences of variable level of complexity.Item Shape matching using set of curve geometric invariant point(Václav Skala - UNION Agency, 2005) Pintavirooj, C.; Nantivatana, P.; Putjarupong, P.; Withayachumnankul, W.; Sangworasil, M.; Skala, VáclavWe introduce a non-iterative geometric-based method for shape matching using a novel set of geometric landmarks residing on a 2D contours. These landmarks are intrinsic and are computed from the differential geometry of the curve. We exploit the invariant properties of geometric landmarks that are local and preserved under the affine and some perspective transformation. Geometric invariant exploits coplanar five-point invariant and ration of area constructed from a sequence of consecutive landmarks. These invariants are preserved not only in affine map but weak perspective map as well. To reduce the sensitivity of the landmarks to noise, we use a B-Spline surface representation that smoothes out the curve prior to the computation of the landmarks. The matching is achieved by establishing correspondences between the landmarks after a conformal sorting based on derived absolute invariant and registering the contours. The experiments have shown that the purposed methods are robust and promising even in the presence of noise.Item 3D Modeling from Multiple Projections: Parallel-Beam to Helical Cone-Beam Trajectory(Václav Skala - UNION Agency, 2005) Narkbuakaew, W.; Pintavirooj, C.; Withayachumnankul, W.; Sangworasil, M.; Taertulakarn, S.; Skala, VáclavTomographic imaging is a technique for exploration of a cross-section of an inspected object without destruction. Normally, the input data, known as the projections, are gathered by repeatedly radiating coherent waveform through the object in a number of viewpoints, and receiving by an array of corresponding detector in the opposite position. In this research, as a replacement of radiographs, the series of photographs taken around the opaque object under the ambient light is completely served as the projections. The purposed technique can be adopted with various beam geometry including parallel-beam, cone-beam and spiral cone-beam geometry. From the process of tomography, the outcome is the stack of pseudo cross-sectional image. Not the internal of cross section is authentic, but the edge or contour is valid.Item Acceleration of Genetic Algorithm with Parallel Processing with Application in Medical Image Registration(Václav Skala - UNION Agency, 2005) Laksanapanai, B.; Withayachumnankul, W.; Pintavirooj, C.; Tosranon, P.; Skala, VáclavGenerally, image registration using genetic algorithm is a time-consuming process since the algorithm needs to evaluate the objective function several hundred times depending on the vastness of search space. The situation appears worse if the registration is intensity-based due to the interpolation loops prior to each objective function. However, with the availability of parallel processing method, one can accelerate the application of genetic algorithm for iterative-based image registration process of up 80 % for multi-modality alignment.Item Line Correspondences Between Two Images Using Local Affine Moment Invariant(Václav Skala - UNION Agency, 2005) Chan, C. H.; Hung, Y. S.; Leung, C. H.; Skala, VáclavThis paper proposes an algorithm for matching line segments between two images which are related by affine transformations using local affine moment invariant (AMI). Instead of using traditional methods for objection recognition in which each object is globally represented by a vector of affine moment invariants, here each pair of line segments extracted from each image is locally represented by an affine moment invariant. This algorithm is suitable for line correspondences with multi-planes and occlusion. Matches are determined through comparing invariant values and voting. Experimental results are given for both synthetic and real images. The noise model of affine moment invariant is also presented.Item Photographic Depth of Field Blur Rendering(Václav Skala - UNION Agency, 2005) Pichard, Cyril; Sylvain, Michail; Tubach, Olivier; Skala, VáclavThe purpose of our study is to introduce a new method for depth of field blur simulation used for compositing real and synthetic images in a realistic way. Existing methods do not simulate accurately the depth of field blur produced by photographic equipment. The problem is twofold: photometric and geometric. Existing methods based on convolution do not produce a realistic photometric rendering compared to real photograph and the photographic blur contains patterns associated with the diaphragm shape, neither handled by existing methods. Our method, based on image processing, addresses these two issues by following the photographic image creation process. It can be used on synthetic or real images, essentially for special effects compositing.Item Geometrical accuracy of Bayer pattern images(Václav Skala - UNION Agency, 2005) Perko, Roland; Fürnstahl, Philipp; Bauer, Joachim; Klaus, Andreas; Skala, VáclavModern digital still cameras sample the color spectrum using a color filter array coated to the CCD array such that each pixel samples only one color channel. The result is a mosaic of color samples which is used to reconstruct the full color image by taking the information of the pixels’ neighborhood. This process is called demosaicking. While standard literature evaluates the performance of these reconstruction algorithms by comparison of a ground-truth image with a reconstructed Bayer pattern image in terms of grayscale comparison, this work gives an evaluation concept to asses the geometrical accuracy of the resulting color images. Only if no geometrical distortions are created during the demosaicking process, it is allowed to use such images for metric calculations, e.g. 3D reconstruction or arbitrary metrical photogrammetric processing.Item Evaluation of Modern Dynamic Programming Algorithms for Real-time Active Stereo Systems(Václav Skala - UNION Agency, 2005) Nahmias, J. D.; Steed, A.; Buxton, B.; Skala, VáclavStereo Vision has been an active research field that has produced a variety of different algorithms. Unfortunately most of the algorithms that produce superior results rely on non-linear optimization techniques that are very computationally expensive, and therefore not feasible to use for real-time applications such as tele-immersion. This paper will examine a number of real-time stereo algorithms based on dynamic programming (DP) used in conjunction with structured light in order to improve the quality and facilitate the correspondence search. We will examine some of the early DP algorithms as well as the more recent work produced by [Criminisi et al] for the purpose of Gaze manipulation for teleconferencing in the context of 3d reconstruction. We present adaptation of [Birchfield et al] DP algorithm to work with structured light. Additional we look at spatialtemporal support region for computing matching costs.Item Occlusion Culling with Statistically Optimized Occlusion Queries(Václav Skala - UNION Agency, 2005) Kovalčík, Vít; Sochor, Jiří; Skala, VáclavThis paper presents an effective algorithm for occlusion culling using hardware occlusion queries. The number of queries is optimized according to the results of the queries from several preceding frames. Parts of the scene which are found to be unoccluded in recent frames, are tested less often thus reducing the number of queries performed per frame. The algorithm is applicable to any kind of scene, including scenes with moving objects. The algorithm utilizes a tree structure containing objects in the scene.Item Image-Based Point Rendering and Its Application to Color Editing Tool(Václav Skala - UNION Agency, 2005) Kawata, Hiroaki; Gouaillard, Alexandre; Morita, Masahiko; Kohiyama, Kenji; Kanai, Takashi; Skala, VáclavAdvances in 3D scanning technologies have enabled the practical creation of hundreds of millions of points. In this paper, we describe a novel image-based point rendering algorithm only using points. Most of previous point rendering algorithms has to prepare normal vectors in advance to establish shading effects. Our algorithm is based on image processing and can calculate normal vectors on the fly in each frame using principal component analysis. Also, our algorithm is familiar with various other image processing algorithms. As an example we demonstrate an interactive color-editing tool for points.Item Towards Invariant Interest Point Detection of an Object(Václav Skala - UNION Agency, 2005) Islam, Mohamed Saiful; Sluzek, Andrzej; Lin, Zhu; Skala, VáclavDetection of some interest points on an object is useful for many applications, such as local shape description of the object, recognition of the object in clutter environment etc. The same object present in different images can have some geometric and photometric transformations with respect to one another. The detection method should be robust to all these transformations. We describe relative scale Harris method for interest point detection. This method is robust to linear geometric transformations. A threshold selection method is also described for invariance to intensity change, partial occlusion and clattered environment. Unlike multi-scale methods our method is fast enough to be suitable for real time applications.
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