WSCG 2010: Communication Papers Proceedings
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Item Surface Curvature Effects on Reflectance from Translucent Materials(Václav Skala - UNION Agency, 2010) Kolchin, Konstantin; Skala, VáclavMost of the physically based techniques for rendering translucent objects use the diffusion theory of light scattering in turbid media. The widely used dipole diffusion model [JMLH01] applies the diffusion-theory formula derived for the planar surface to objects of arbitrary shapes. The purpose of this communication paper is to present the very first results of our investigation of how surface curvature affects the diffuse reflectance from translucent materials.
Item Fingerprint Alignment Based on Local Feature Combined with Affine Geometric Invariant(Václav Skala - UNION Agency, 2010) Pintavirooj, Chuchart; Cohen, Fernand S.; Iampa, Woranut; Skala, VáclavIn this paper we introduce a novel method of fingerprint alignment that uses the intrinsic geometric properties of minutiae-based triangles combined with the geometric invariant. The minutiae points are extracted from the fingerprint image and a Delaunay (DL) triangulation is constructed from these minutiae points resulting in a series of triangles. Corresponding minutiae points are established using local affine invariants constructed from the local minutia-based triangles. Triangles that are distorted by noise or have no counter part on the query are discarded. We rely only on “strong” matches that are reliable and present, for example, where the error metric between the local absolute invariants is below a set threshold. The correspondences of such matches are then used to estimate transformation parameters. The performance of our method is represented by computing the distance map error between a template and a query fingerprint after undoing the transformation, computed from the ridge structures of the two fingerprints. In conclusion, the proposed method can be used to find the corresponding minutiae and align any fingerprints considered into affine transformation, in the presence of noise including the partial occlusion.Item A Novel Image Transformation For Solving Complex Image Mapping Problems(Václav Skala - UNION Agency, 2010) Maslov, Igor V.; Detkova, Yulia D.; Gertner, Izidor; Skala, VáclavThe paper proposes a novel image transformation called Image Local Response (ILR) that can be used for solving complex image mapping problems. The proposed transformation brings together two approaches based on the pixel value distribution and image features. Image local response is defined as the average value of the difference between the transformed and the original copies of the same image whereby the transformation is small, i.e., the components of the corresponding parameter vector have sufficiently small unit values. The response has a few interesting properties useful in image mapping. The validity of the proposed image transformation is shown on sample complex image mapping problems formulated as the multi-objective piecewise imaging optimization problem.Item Interactive Ray Tracing Client(Václav Skala - UNION Agency, 2010) Radziszewski, Michal; Alda, Witold; Boryczko, Krzysztof; Skala, VáclavIn this paper we present an interactive GPU-based, GUI client, working with rendering server employing ray tracing based global illumination. The client is designed to guarantee interactivity (namely 1/60sec response time) no matter how slow the rendering server is. The client dynamically adjusts image resolution to match the server performance and complexity of the rendered scene. When the scene is modified, the image may appear out of focus and noisy, depending on the machine computational power, but usually is readable. With no interrupt from the client, the image is progressively improved with new data from the server. The system expliots hybrid programming model – CPU for the server and GPU for the client.Item Markov Random Fields on Triangle Meshes(Václav Skala - UNION Agency, 2010) Andersen, Vedrana; Aanæs, Henrik; Bærentzen, Andreas; Nielsen, Mads; Skala, VáclavIn this paper we propose a novel anisotropic smoothing scheme based on Markov Random Fields (MRF). Our scheme is formulated as two coupled processes. A vertex process is used to smooth the mesh by displacing the vertices according to a MRF smoothness prior, while an independent edge process labels mesh edges according to a feature detecting prior. Since we should not smooth across a sharp feature, we use edge labels to control the vertex process. In a Bayesian framework, MRF priors are combined with the likelihood function related to the mesh formation method. The output of our algorithm is a piecewise smooth mesh with explicit labelling of edges belonging to the sharp features.Item Multi-Threaded Real-Time Video Grabber(Václav Skala - UNION Agency, 2010) Trávníček, Zdeněk; Berka, Roman; Skala, VáclavCommunication in general incorporates technologies with increasing number of communication modes. Special applications are developed in the area of virtual reality, multimedia communications and others where combinations of audio, video, 3D data are sent between two (or more) distant users which can commonly interact with these data. A form of so exchanged information usually requires, among others, special forms of presentation. Thus stereoscopic and virtual reality visualization devices are used to present intricately structured information in multi-modal form. There are situations where the presented information is to be rendered in real-time and transmitted to the remote user in form of a video-stream. In this case, the content is presented on a local visualization device (e.g. CAVE) being simultaneously sent to a remote device. Thus a method how to obtain rendered data from graphics hardware in real-time is necessary. The problem is, how to obtain the rendered data for transmission with minimal impact on the rendering and visualization process. In this paper, we present a method how to retrieve video stream from an arbitrary running OpenGL application, capturing every frame with minimal impact on performance.Item Image Authentication Using Robust Image Hashing with Localization and Self-Recovery(Václav Skala - UNION Agency, 2010) Hassan, Ammar M.; Hasan, Yassin M. Y.; Wahab, Mohamed A. A.; Skala, VáclavThe rapid growth of efficient tools, which generate and edit digital images demands effective methods for assuring integrity of images. A semi-fragile block-based image authentication technique is proposed which can not only localize the alteration detections but also recover the missing contents. The proposed technique distinguishes content-preserving manipulations from the content alterations using secure image hashing instead of cryptographic hashing. The original image is divided into large blocks (sub-images) which are also divided into 8×8 blocks. Secure image hashing is utilized to generate the sub-image hash (signature) which may slightly change when the content-preserving manipulations are applied. Furthermore, the sub-image code is generated using the JPEG compression scheme. Then, two sub-image hash copies and the sub-image code are embedded into relatively-distant sub-images using a doubly linked chain which prevents the vector quantization attack. The hash and code bits are robustly embedded in chosen discrete cosine transform (DCT) coefficients exploiting a property of DCT coefficients which is invariant before and after JPEG compression. The experimental results show that the proposed technique can successfully both localize and compensate the content alterations. Furthermore, it can effectively thwart many attacks such as vector quantization attacks.Item RenderManʼs Power to Visualizationʼs Rescue(Václav Skala - UNION Agency, 2010) Espinal, Julio; Allen, Virginia; Amable, Kwesi; Bailey, Reynold; Bischof, Hans-Peter; Skala, VáclavMost visualization systems employ a data flow approach in order to create visual representations of data. The data flows along a directed graph through the different components, gets filtered, extracted, analyzed, and finally converted into an image. Most visualization systems use one graphic toolkit or library to create the image. These toolkits and libraries are not created equally; some are better suited than others to solve given problems. Being able to pick and choose would often generate a better result. Within the Spiegel framework any toolkit, which can be used in a Java environment, can be employed to create the image. In this paper, we explain the Spiegel framework and how Pixar's PhotoRealistic RenderMan® can be used to visualize scientific data.Item Automatic Generation of Character Behavior by the Placement of Objects with Motion Data(Václav Skala - UNION Agency, 2010) Kobori, Kenichi; Hirose, Kenji; Nishio, Kijo; Skala, VáclavRecently, virtual space design with high quality three-dimensional CG has become possible due to a rapid improvement in computer performance. In order to give a CG character the movement of its own, it is necessary to apply the motion data to the character after getting them with a motion capture device or by hand work. Production costs have increased because this is complicated work for an animator. In general, the character movement depends on the objects which it holds. Our idea is that the character does not have motion data of its own, but we give the character motion to the objects that it holds. We have developed a method for automatically generating the character motion data by giving motion information to the objects. Thus, each object includes the motion data that cause the character to act. In addition, we give multiple motion data appropriate for the situations to the objects and define the relationship between objects in a virtual space. By using this relation, we can generate a variety of motion data according to the object which the character holds. The proposed method reduces the number of character motion data which should be prepared beforehand.Item A User-Adaptive Image Browsing System with Summarization Layout for the Personal Photo Collections(Václav Skala - UNION Agency, 2010) Ryu, Dong-Sung; Jang, Chul Jin; Cho, Hwan-Gue; Skala, VáclavUsers spend much time organizing photos into small groups as part of photo management. Selecting good quality photos and organizing them is burdensome, as photographers amass large number of photos. This paper presents a new photo layout system with representative photos considering multiple features. Our approach consists of three steps to deal with hundreds of photos. First, we construct photo clusters by user-adapted criteria: temporal context, the number of faces, blur and luminance metrics. Then, we construct a bipartite graph that consists of photo nodes in a partite set and the constructed cluster nodes in other partite set. The representative photos of each cluster are selected by a maximal matching algorithm based on user-controlled multiple criteria. Finally, our system places the selected representative photos on a 2D grid using the placement algorithm of PHOTOLAND. Other photos in each cluster are displayed in an upper layer of a screen when the user clicks the representative photo. We conducted an experiment based on a user study; it used nine photo sets taken on a trip. The experiment showed that our system conveniently managed hundreds of photos, summarizing and visualizing them.Item Active Shape Models on adaptively refined mouth emphasizing color images(Václav Skala - UNION Agency, 2010) Panning, Axel; Al-Hamadi, Ayoub; Michaelis, Bernd; Skala, VáclavIn this paper, we propose a hybrid method for lip segmentation based on normalized green-color histogram splitting and Active Shape Models (ASM). A new adaptive method for histogram splitting is applied in two steps. First, after defining a region of interest for mouth segmentation, a rough adaptive threshold selects a histogram region assuring that all pixels in that region are skin pixels. Second, based on these pixels, we build a Gaussian model which represents the skin pixels distribution and is used to obtain a refined optimal threshold for lip pixel classification. This process is used to refine the normalized green channel image for the elimination of inner distortions and gradients inside the lip region, which can misguide active contours (i.e. ASM) in the last step of the hybrid segmentation process. In the results, we present that the proposed method performed better than conventional ASM on unrefined color enhanced images or pure color-histogram based mouth segmentation.Item A system for panoramic navigation inside a 3D environment(Václav Skala - UNION Agency, 2010) Mihai, Polceanu; Alexandru, Popovici; Dorin-Mircea, Popovici; Skala, VáclavThis paper presents a physical user interface intended to help the user (or multiple simultaneous users) to achieve an intuitive movement inside a 3D environment without using common interaction devices such as mouse or keyboard, while stressing the aspect of reducing financial investments. After exposing an analysis of current solutions and implementations of related topics, we argument our implementation and give detailed aspects of hardware and software architecture of the system, as well as a comprehensive efficiency study and explore the use cases with people with motor impairment. As future work, we intend to extend the usability of the system and release it under the GNU General Public License (GPL) for free use and further development by other parties.Item High-Quality Wavelet Compressed Textures for Real-time Rendering(Václav Skala - UNION Agency, 2010) Grund, Nico; Menzel, Nicolas; Guthe, Michael; Skala, VáclavAlthough modern graphics hardware provides up to 1.5 gigabytes of memory, methods for effective texture compression are still required since there is always demand for more detailed and realistic images. In this paper, we present a method for the effective compression of large images and textures based on a quadratic B-Spline wavelet. The transformation is followed by a tree-compaction algorithm, which achieves high compression ratio at good image quality.Item New methods for progressive compression of colored 3D Mesh(Václav Skala - UNION Agency, 2010) Lee, Ho; Lavoué, Guillaume; Dupont, Florent; Skala, VáclavIn this paper, we present two methods to compress colored 3D triangular meshes in a progressive way. Although many progressive algorithms exist for efficient encoding of connectivity and geometry, none of these techniques consider the color data in spite of its considerable size. Based on the powerful progressive algorithm from Alliez and Desbrun [All01a], we propose two extensions for progressive encoding and reconstruction of vertex colors: a prediction-based method and a mapping table method. In the first one, after transforming the initial RGB space into the Lab space, each vertex color is predicted by a specific scheme using information of its neighboring vertices. The second method considers a mapping table with reduced number of possible colors in order to improve the rate-distortion tradeoff. Results show that the prediction method produces quite good results even in low resolutions, while the mapping table method delivers similar visual results but with a fewer amount of bits transmitted depending on the color complexity of the model.Item Interactive Stipple Rendering for Point Clouds(Václav Skala - UNION Agency, 2010) Awano, Naoyuki; Nishio, Koji; Kobori, Ken-ichi; Skala, VáclavNon-photorealistic rendering has been attracting attention in the field of computer graphics. A common approach to artistic rendering is using a shape model which utilizes mesh data. In recent years, the use of point clouds as shape models has increased due to the rapid development of 3D-scanners used to create them. Correspondingly, there has been an increase in the research on point clouds. We propose a stipple rendering method as a type of artistic rendering for point clouds, based on a hybrid image/object space. First, we eliminate hidden points based on an image space. Next, we apply a novel shading method to the visible points based on an image space. Lastly, we apply the above two results to the input point cloud. We implement the proposed method using a graphics processing unit to accomplish the interactive rendering. The experimental results show that we can achieve shading and shadowing interactively.Item Decomposing the Contact Linear Complementarity Problem into Separate Contact Regions(Václav Skala - UNION Agency, 2010) Lazarevych, Olexiy; Szekely, Gabor; Harders, Matthias; Skala, VáclavWe present a novel approach to handling frictional contacts for deformable body simulations. Our contact model allows to separate the contact area into a set of detached contact regions. For each of them a separate mixed linear complementarity problem (MLCP) is formulated. Parallel processing of these independent contact regions may considerably improve the performance of the contact handling routine. Moreover, the proposed contact model results in sparse matrix formulation of the corresponding MLCP in the individual contact regions. For solving the MLCPs we propose an iterative method which combines the projected conjugate gradient approach and the projected Gauss-Seidel method.Item Chrome, Gold and Silver on the Screen(Václav Skala - UNION Agency, 2010) Wucharz, Julia; Loviscach, Jörn; Skala, VáclavA plausible rendering of metallic effects on a computer display is of high importance for 3D representations—as used in advertising and sales—and for pre-visualizing print designs that include special inks such as gold and/or silver. A human viewer recognizes these materials by their specific reflection properties. Hence, simulating them requires taking the illumination from the environment and the position of the viewer’s head into account. We demonstrate that this can be achieved in a Web-based application that leverages the webcam installed on the user’s computer. Thus, metallic color effects can be made available almost ubiquitously, in particular in Web shops.Item Creating Continuous Force Feedback for Haptic Interaction of Volume Data Sets(Václav Skala - UNION Agency, 2010) Liu, Y.; Laycock, S. D.; Skala, VáclavInteracting with volumetric models via a haptic device presents an effective way of perceiving details concerning the models internal structures. Approaches to facilitate this range from interacting directly with the volume data to interacting with a polygonal surface derived from the data. Previous approaches have utilised a force field to provide continuous forces such as the Force-Map method which assigns a force vector at any position in the virtual environment. Nevertheless, the Force-Map method is still limited in simulating fast moving drilling due to the fact that there are no forces inside the volume. It suffers from a pop through problem when the virtual drill quickly moves against the volume object. To circumvent this problem, the work presented in this paper introduces a Level-Box method to improve the Force-Map method by encoding the object’s internal area into a number of levels which not only enables the user to touch the volume object by using a Force-Map, but also accelerates the Force-Map update procedure when drilling. Users can select from a variety of virtual tools to gain continuous and smooth force feedback during the drilling of volumetric data which increases the applicability of the approach.Item Efficient Reconstruction From Scattered Points(Václav Skala - UNION Agency, 2010) Bíscaro, Helton Hideraldo; Skala, VáclavMost algorithms that reconstruct surface from sample points rely on computationally demanding operations to derive the reconstruction, beside this, most of the classical algorithm use a kind of three-dimensional structure to derive a two-dimensional one. In this paper we introduce an innovative approach for generating two-dimensional piecewise linear approximations from sample points in R3 that simplify significantly the numerical calculation and the memory usage in the reconstruction process. The approach proposed here is an advancing front approach that uses rigid movements in the three-dimensional space and a bidimensional Delaunay triangulation as the main tools for the algorithm. The principal idea is to use a combination of rotations and translations in order to simplify the calculations and avoid the three-dimensional structure used by the most of the algorithms. Avoiding those structures, this approach can reduce the computational cost and numerical instabilities typically associated with the classical algorithm reconstructions.Item Modeling and rendering heterogeneous fog in real-time using B-Spline wavelets(Václav Skala - UNION Agency, 2010) Giroud, Anthony; Biri, Venceslas; Skala, VáclavHeterogeneous fogs are often modeled with several layers of different density or using particle systems. However, layers are limited to vertical variations and using particles can involve a long computation time with large outdoor scenes. In this article we present a simple method to render heterogeneous fog in real-time. The extinction function of our fog, related to its density, is first modeled in a B-Spline function basis. Then, a wavelet transform is applied on this function to obtain a decomposition in both space and frequency domains. A grid traversal is used to render the fog in real time using the GPU. Since no precomputation is required concerning the position of the camera or the fog, we can freely navigate or move the fog into the scene.
