Volume 18, number 1-3 (2010)

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http://hdl.handle.net/11025/1255

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Showing 1 - 17 out of 17 results

Parametric Curves Variations with Respect to a Given Direction
(Václav Skala - UNION Agency, 2010) Bayar, Abdelouahad; Sami, Khalid; Skala, Václav
Modeling dynamic characters, in observance of calligraphic rules can be done with the help of parametric curves. The class of Bézier curves is a powerful tool for modeling the outlines of the surface razed by a nib's calligrapher. Unfortunately, after capturing the character's hand-drawn outlines, the surface delimited by the outlines doesn't correspond to the space to shade when writing the character. Some of the curves pieces of the outlines are to be subdivided at some appropriate points. In order to identify these points, decompositions of the Bézier curves involved, with respect to particular directions, are necessary. This paper presents a simple and e ective mathematical method for doing such decompositions.The proposed method helps to determine the points as extrema of certain functions. Then, the method is implemented and used to design some Arabic dynamical characters. This will help in building dynamic fonts respecting calligraphic strong rules.
Partial 3D shape matching using large fat tetrahedrons
(Václav Skala - UNION Agency, 2010) Vergeest, Joris S. M.; Kooijman, A.; Song, Y.; Skala, Václav
We present a method of automatic alignment of two partially matching 3D shapes. The algorithm selects large fat tetrahedrons (LFT) composed of 4 vertices in one shape and exhaustively searches in the other shape for sets of 4 vertices being compatible with the tetrahedron. By selecting such salient tetrahedrons that are relatively wide and fat, although also being not too unlikely to be contained in the overlap region, the cost of search can be reduced. The method is relatively insensitive to noise and not depending on the existence of local shape features nor on feature correspondences. When implemented on a GPU in Cuda, two point sets of 40,000 each can be aligned within seconds. The method is intended to support interactive 3D scan registration applications.
Simulating real-time cloth with adaptive edge-based
(Václav Skala - UNION Agency, 2010) Simnett, T. J. R.; Laycock, R. G.; Day, A. M.; Skala, Václav
We present an approach to simulating detailed cloth in real-time using an adaptive edge-based mesh, by enhancing its usability and performance. We show how simple seaming can be used to combine multiple adaptive meshes into garments, accomplished with the use of discontinuous material co-ordinates. Performance is improved by decoupling the mesh adaption and simulation steps, allowing efficient data structures to be exploited for the simulation and collision detection. Greater memory efficiency is achieved by pre-allocating a pool of memory to be used by any mesh at any hierarchical level. The collision detection process is integrated into the edge-based adaption technique, enabling a garment to be coarsened and refined repeatedly, such that no new vertices are created inside of the object in collision. Our technique is illustrated for a 67k triangle character wearing a T-shirt adaptively refined to 6k triangles in real-time.
A new CBIR approach based on relevance feedback and optimum-path forest classification
(Václav Skala - UNION Agency, 2010) da Silva, André Tavares; Xavier, Alexandre; Magalhães, Léo Pini; Skala, Václav
Recently some CBIR approaches have shown the use of relevance feedback to train a pattern classifier to select relevant images for retrieval. This paper revisits this strategy by using an optimum-path forest (OPF) classifier. During relevance feedback iterations, the proposed method uses the OPF classifier to decide which database images are relevant or not. Images classified as relevant are sorted and presented to the user for a new iteration. Such images are ordered according to the normalized distance using relevant and irrelevant representative images, computed previously by the OPF classifier. Our experiments show that the proposed approach requires fewer iterations, being faster and more effective than methods based on SVM.
PhotoPath: single image path depictions from multiple photographs
(Václav Skala - UNION Agency, 2010) Schwartz, Christopher; Schnabel, Ruben; Degener, Patrick; Klein, Reinhard; Skala, Václav
In this paper we present PhotoPath, an image synthesis technique that allows the visualization of paths through real world environments in a single intuitive picture. Given a series of input photographs taken with a hand-held camera along the path, our method generates an image that creates the impression of looking along the path all the way to the destination regardless of any curves or corners in the route. Rendered from a pedestrian perspective, this visualization supports intuitive wayfinding and orientation while avoiding occlusion of path segments in the image. Our approach intentionally avoids an involved and error-prone scene reconstruction. Instead we advocate the use of planar geometry proxies estimated from the sparse point-cloud obtained with Structure-from-Motion. The proxy geometry is spatially deformed in order to align the curved path with the straight viewing direction of the synthesized view. Finally, we propose a novel image composition algorithm accommodating for parallax and occlusion artifacts due to the approximation errors of the actual scene geometry.
Screen space ambient occlusion for virtual and mixed reality factory planning
(Václav Skala - UNION Agency, 2010) Scheer, Fabian; Keutel, Michael; Skala, Václav
Ambient occlusion represents one aspect of global illumination, simulating the actual accessibility of surfaces for indirect illumination due to occlusion of nearby geometry. Recently the approximation in screen space made it feasible for realtime applications. We focus on the utilization of screen space ambient occlusion (SSAO) in virtual and mixed reality environments, especially considering scenes with a large spatial extent and massive amounts of data, typical for industrial factory planning scenarios. Therefore, a sophisticated screen space approach closer to the original definition of ambient occlusion is presented and compared with existing techniques considering the visual quality. Furthermore, we introduce a method to avoid the disappearance of the SSAO effect in depth for scenes with a large spatial extent. A user study compares the impact of our approach to standard SSAO and standard phong shading, regarding the several cues of human depth perception in a virtual and a mixed reality scenario. The evaluation underlines the benefit of our approach for pure virtual scenes and additionally illustrates a different perception of the cues regarding virtual scenes with a half transparent overlayimage of the real world, typical for mixed reality discrepancy check scenarios.
A threefold representation for the adaptive simulation of embedded deformable objects in contact
(Václav Skala - UNION Agency, 2010) Seiler, Martin; Spillmann, Jonas; Harders, Matthias; Skala, Václav
We propose an approach for the interactive simulation of deformable bodies. The key ingredient is a threefold representation of the body. The deformation and dynamic evolution of the body is governed by a cubic background mesh. The mesh is hierarchically stored in an octree-structure, allowing for a fully local adaptive refinement during the simulation. To handle collisions, we employ a tetrahedral mesh, allowing for an efficient collision detection and response. We then show a physicallyplausible way to transfer the contact displacements onto the simulation mesh. A high-resolution surface is embedded into the tetrahedral mesh and only employed for the visualization. We show that by employing the adaptive threefold representation, we can significantly improve the fidelity and efficiency of the simulation. Further, we underline the wide applicability of our method by showing both interactive and off-line animations.
Evolving time surfaces in a virtual stirred tank
(Václav Skala - UNION Agency, 2010) Bohara, Bildur; Harhad, Farid; Benger, Werner; Brener, Nathan; Ritter, Marcel; Liu, Kexi; Ullmer, Brygg; Somnath, Roy; Acharya, Sumanta; Iyengar, S. Sitharama; Karki, Bijaya B.; Skala, Václav
The complexity of large scale computational fluid dynamic simulations demand powerful tools to investigate the numerical results. Time surfaces are the natural higher-dimensional extension of time lines, the evolution of a seed line of particles in the flow of a vector field. Adaptive refinement of the evolving surface is mandatory for high quality under reasonable computation times. In contrast to the lower-dimensional time line, there is a new set of refinement criteria that may trigger the refinement of a triangular initial surface, such as based on triangle degeneracy, triangle area, surface curvature etc. In this article we describe the computation of time surfaces for initially spherical surfaces. The evolution of such virtual “bubbles” supports analysis of the mixing quality in a stirred tank CFD simulation. We discuss the performance of various possible refinement algorithms, how to interface alternative software solutions and how to effectively deliver the research to the end-users, involving specially designed hardware representing the algorithmic parameters.
Component-based isosurface extraction for multiple dataset visualization
(Václav Skala - UNION Agency, 2010) Gu, Shiyuan; Karki, Bijaya B.; Skala, Václav
In the situations where isosurfaces are comprised of many disjoint components, two or more datasets can be visualized simul- taneously by processing only a subset of isosurface components. The components of interest can be selected by exploiting interdataset coherency at the level of individual voxels and components. Thus, only those components (identified as voxel cov- erages or voxel sets) which differ significantly among the datasets under consideration are extracted as needed while the similar components were extracted only once from a reference dataset. Since the polygons are extracted/rendered as a whole com- ponent, the rendered isosurfaces are crack-free. We use three user-defined thresholds to control multiple dataset visualization (MDV) so that important relationships (differences and similarities) among the datasets can be explored with an improvement in the overall performance. If the data-coherency can not be defined easily, MDV can still benefit from the on-the-fly processing of the individual components.
Stable explicit integration of deformable objects by filtering high modal frequencies
(Václav Skala - UNION Agency, 2010) Fierz, Basil; Spillmann, Jonas; Harders, Matthias; Skala, Václav
In a traditional finite element method for the simulation of deformable objects, the stiffness matrix depends on the shape of the tetrahedral elements. Ill-shaped elements containing large or small dihedral angles lead to an arbitrary large condition number of the stiffness matrix, thus slowing down the simulation. In addition, high modal frequencies cannot be simulated stably if an explicit numerical time-integration scheme is considered. We propose an approach consisting of two components to address this problem: First, we isolate the ill-shaped tetrahedra by performing an eigenvalue decomposition, and then remove their high modal frequencies by directly altering their element stiffness matrices. This makes the elements softer in some directions. To prevent element inversion, we define constraints that rigidify the object along those directions. The fast projection method, implemented as a velocity filter, is employed to enforce the constraints after the temporal evolution. With our approach, a significantly larger time step can be chosen in explicit integration methods, resulting in a faster simulation.
Complex geometric primitive extraction on graphics processing unit
(Václav Skala - UNION Agency, 2010) Değirmenci, Mert; Skala, Václav
Extracting complex geometric primitives from 2-D imagery is a long-standing problem that researchers have had to deal with. Various approaches were tried from Hough transform based methods to stochastic algorithms. However, serial implementations lack sufficient scalability on high resolution imagery. As sequential computing power cannot pace up with the increase in size of datasets, researchers are compelled to exploit parallel computational resources and algorithms. In this study, we have merged parallelization capability of GPUs with inherent parallelism on genetic algorithms to cope with the problem of detecting complex geometric primitives on high resolution imagery. We have implemented ellipse detection on commodity graphics processing unit and showed that our GPU implementation achieve high speed-up relative to state of the art CPU by experimental results.
Divergence analysis of discrete 2-d shapes
(Václav Skala - UNION Agency, 2010) Brunner, David; Brunnett, Guido; Skala, Václav
In this paper we introduce a second order differential operator in order to partition discrete objects into meaningful parts. One of these parts contains all points of the object’s medial axis which is a widely used shape descriptor. Since aliasing is a fundamental problem for methods based on the boundary of discrete objects we use a bilateral filter to reduce the artefacts significantly. As a result of the partitioning and filtering we obtain a lattice point set (a superset of the medial axis) which is robust against noise and aliasing and which is rotationally invariant. The lattice point set can be used for instance to compute the medial axis or similar shape descriptors.
Automated motion LoD with rigid constraints
(Václav Skala - UNION Agency, 2010) Ahn, Junghyun; Kim, Byung-Cheo; Thalmann, Daniel; Wohn, Kwangyun; Skala, Václav
Motion LoD (Level of Detail) is a preprocessing technique that generates multiple details of captured motion by eliminating joints. This LoD technique is applied to movie, game or VR environments for the purpose of improving speed of crowd animation. So far, replacement techniques such as ‘impostor’ and ‘rigid body motion’ are widely used on real-time crowd, since they dramatically improve speed of animation. However, our experiment shows that the number of joints has a greater effect on the animation speed than anticipated. To exploit this, we propose a new motion LoD technique that not only improves the speed but also preserves the quality of motion. Our approach lies in between impostor and skeletal animation, offering seamless motion details at run time. Joint-elimination priority of each captured motion is derived from joint importance, which is generated by the proposed posture error equation. Considering hierarchical depth and rotational variation of joint, our error equation measures posture difference successfully and allows finding key posture of the entire motion. This ‘motion analysis’ process contributes error reduction to the next ‘motion simplification’ stage, where multiple details of motion are regenerated by the proposed motion optimization. In order to reduce the burden of optimization, all the terms of the objective function - distance, string, and angle error - are defined by joint-position vectors. In this aspect, a constrained optimization problem is formulated in a quadratic form. Thus, a sequential quadratic programming (SQP), a nonlinear optimization method, is suitable for resolving this problem. As the result of our experiment, the proposed motion LoD technique improves the animation speed and visual quality of simplified motion. Moreover, our approach reduces the preprocessing time and automates the whole process of LoD generation.
Accelerated streak line computation using adaptive refinement
(Václav Skala - UNION Agency, 2010) Wiebel, Alexandr; Wang, Qin; Schneider, Dominic; Scheuermann, Gerik; Skala, Václav
We introduce an improved algorithm for streak line approximation in 2D and 3D time-dependent vector fields. The algorithm is mainly based on iterative refinement of an initial coarse approximation of the streak line. The refinement process is steered by a predicate indicating the local approximation quality. We apply the algorithm to several real-world data sets to prove its applicability and robustness. An error analysis and a comparison show that the algorithm produces more accurate streak lines in shorter time compared to previous approaches. Finally we show how the new algorithm can help to improve the construction of streak surfaces.
A secure touch-less based fingerprint verification system
(Václav Skala - UNION Agency, 2010) Yan, Hiew Bee; Beng Jin, Andrew Teoh; Ooi Shih, Yin; Abdul Aziz, Fathin Fakhriah; Skala, Václav
Touch-less based fingerprint verification systems are free from the problems of image deformation, latent fingerprint issues and so forth that appear in the contemporary touch based fingerprint verification systems. Coupled with template protection mechanism, a touch-less fingerprint verification system is further enhanced. In this paper, a secure end-to-end touch-less fingerprint verification system is presented. The fingerprint image captured with a digital camera is first pre-processed via the proposed pre-processing algorithm. Then, Multiple Random Projections-Support Vector Machine (MRP-SVM) is proposed to secure fingerprint template while improving system performance.
Visualization of the continental drift in real-time
(Václav Skala - UNION Agency, 2010) Rogge, Lorenz; Lipski, Christian; Magnor, Marcus; Skala, Václav
We present an approach to simulate and visualize the paleontological change of the terrestrial globe through time. As input, maps of the Earth at different points in time, each showing a specific stage in the Earth’s development, are used. To display the continuous change of Earth through time, smooth transitions between consecutive input maps are computed by manual correspondence matching. Our system makes it is possible to display the Earth’s paleogeographic development as an interactive globe in real-time.
Interactive shadow design tool for cartoon animation -KAGEZOU-
(Václav Skala - UNION Agency, 2010) Sugimoto, Shiori; Nakajima, Hidehito; Shimotori, Yohei; Morihsima, Shigeo; Skala, Václav
In traditional 2D Anime, shadows are drawn by hand, and play a significant role in the creation of symbolic visual effects related to the character’s position and shape. However shadows are not always drawn as a result of time constraints and a lack of animators. We develop a shadow generation system that enables animators to easily create shadow animation layers based on character outlines. Our system is both simple and intuitive. The only inputs required are the character animation layers generally used in the Anime industry. Shadows are automatically generated based on these inputs, and then generated shadows are fine-tuned by simple mouse operations. First, shadows are rendered using Shadow Map Method based on the transparency information of the character animation layers. Subsequently, our system applies some filters that enable the generated shadow shape to convert into the effective shadow shape such as the elliptical shape or the wavy shape. Through these processes, our system enables animators to create simple Anime-like shadow animation easily and in a short time.

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