Number 1-3 (2009)
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Item Prefiltered gradient reconstruction for volume rendering(Václav Skala - UNION Agency, 2009) Csébfalvi, Balázs; Domonkos, Balázs; Skala, VáclavThe quality of images generated by volume rendering strongly depends on the applied continuous reconstruction method. Recently, it has been shown that the reconstruction of the underlying function can be improved by a discrete prefiltering. In volume rendering, however, an accurate gradient reconstruction also plays an important role as it provides the surface normals for the shading computations. Therefore, in this paper, we propose prefiltering schemes in order to increase the accuracy of the estimated gradients yielding higher image quality. We search for discrete prefilters of minimal support which can be efficiently used in a preprocessing as well as on the fly.
Item Hybrid sort-first/sort-last rendering for dense material particle systems(Václav Skala - UNION Agency, 2009) Latapie, Simon; Skala, VáclavThis paper describes a solution designed for efficient visualization of large and dense sets of particles, typically generated by molecular dynamics simulations in materials science. This solution is based on a hybrid distributed sort-first/sort-last architecture, and meant to work on a generic commodity cluster feeding a tiled display. The package relies on VTK framework with various extensions to achieve statistical occlusion culling, smart data partitioning and GPU-accelerated rendering.Item GPU-based responsive grass(Václav Skala - UNION Agency, 2009) Jens, Orthman; Salama, Christof Rezk; Kolb, Andreas; Skala, VáclavLarge natural environments are often essential for todays computer games. Interaction with the environment is widely implemented in order to satisfy the player’s expectations of a living scenery and to help increasing the immersion of the player. Within this context our work describes an efficient way to simulate a responsive grass layer with todays graphics cards in real-time. Clumps of grass are approximated by two billboard representations. GPU-based distance maps of scene objects are employed to test for penetrations and for resolving them. Adaptive refinement is necessary to preserve the shape of deformed billboards. A recovering process is applied after the deformation which restores the original that is to say the undeformed and efficient shape. The primitives of each billboard are assembled during the rendering process. Their vertices are dynamically lit within an ambient occlusion based irradiance volume. Alpha-to-Coverage completes the illusion as it is used to simulate the semitransparent nature of grass.Item Interactive exploration of large event datasets in high energy physics(Václav Skala - UNION Agency, 2009) Hermann, Max; Greß, Alexander; Klein, Reinhard; Skala, VáclavIn high energy physics the structure of matter is investigated through particle accelerator experiments where particle collisions (events) occur at such high energies that new particles are produced. Providing tools for interactive visual inspection of billions of such events occurring in an experiment in an intuitive way is a challenging task. In order to solve this problem we built on previous approaches for visual browsing through image databases and extend them in several ways in order to allow efficient navigation through the collision event datasets. The key features of our novel browsing technique are its applicability to the very large event datasets, a more intuitive selection method for specifying a region of interest, and finally a clustering-based technique that further simplifies and improves the navigation process. We demonstrate the potential of our novel visual inspection system by integrating it into an event display application for the COMPASS experiment at CERN.Item A novel system for automatic hand gesture spotting and recognition in stereo color image sequences(Václav Skala - UNION Agency, 2009) Elmezain, Mahmoud; Al-Hamadi, Ayoub; Michaelis, Bernd; Skala, VáclavAutomatic gesture spotting and recognition is a challenging task for locating the start and end points that correspond to a gesture of interest in Human-Computer Interaction. This paper proposes a novel gesture spotting system that is suitable for real-time implementation. The system executes gesture segmentation and recognition simultaneously without any time delay based on Hidden Markov Models. In the segmentation module, the hand of the user is tracked using mean-shift algorithm, which is a non-parametric density estimator that optimizes the smooth similarity function to find the direction of hand gesture path. In order to spot key gesture accurately, a sophisticated method for designing a non-gesture model is proposed, which is constructed by collecting the states of all gesture models in the system. The non-gesture model is a weak model compared to all trained gesture models. Therefore, it provides a good confirmation for rejecting the non-gesture pattern. To reduce the states of the non-gesture model, similar probability distributions states are merged based on relative entropy measure. Experimental results show that the proposed system can automatically recognize isolated gestures with 97.78% and key gestures with 93.31% reliability for Arabic numbers from 0 to 9.Item Interactively refining object-recognition system(Václav Skala - UNION Agency, 2009) Eissele, Mike; Sanftmann, Harald; Ertl, Thomas; Skala, VáclavExisting techniques for object recognition often make use of a combination of multiple algorithms and sensors to achieve adequate results. In this paper we propose a real-time system to efficiently combine multiple object-recognition techniques, appropriate for mobile Augmented Reality applications. We focus on the challenge to differentiate objects with only marginal distinguishing features that can often only be identified from specific points of view, and solve this problem by interactively guiding the user during the recognition process. The system is based on a hierarchy to organize model data and control the corresponding feature-detection techniques as shown in a prototypical implementation. Furthermore, recognition techniques are chosen based on context information, e.g. feature type, reliability of sensor data, etc.Item Reconstructing indoor scenes with omni-cameras(Václav Skala - UNION Agency, 2009) Bauer, Frank; Meister, Martin; Stamminger, Marc; Skala, VáclavWe present a system similar to Debevec’s Facade [DTM96] that improves the reconstruction of indoor scenes from photographs. With confined spaces it is often impractical to use regular photos as the base of the reconstruction. Combining pinhole cameras with fisheye shoots or photographs of any kind of reflective, parametrisable body such as light probes eases this problem. We call the later camera setup an omni-camera, because it enables us to acquire as much information as possible from a given viewpoint. Omni-cameras make it possible to reconstruct the geometry of an entire room from just one view. Removing the pinhole camera constraint invalidates some key assumptions made in Facade. This paper shows how to work around the problems arising from this approach by adding scene specific knowledge as well as a genetic component to the solver. When using omni-cameras we can no longer take advantage of a simple texture projection to obtain the materials for the scene. Instead we propose a method for texture generation that is transparent to the camera setup used.Item Simple emphatic user interface for virtual heritage(Václav Skala - UNION Agency, 2009) Stanislav, Staněk; Skala, VáclavWe present a simple user interface combining h-Anim with Perlin’s face. The main application is for exploring virtual environments especially those representing real environments with places, buildings or objects that belong to cultural heritage or those with historical past, famous story or something interesting. Therefore, information about them should be delivered to user. This kind of information is usually full of emotions and that is why the most suitable way (from user interface point of view) is to deliver it with emphatic storytelling. We are introducing our simple emphatic system (implementation uses ActiveX objects, VRML, ECMA Script, Java Script) that uses simple hardware configuration with web cams used for capturing user’s presence and his/her head movements and if possible capturing position of some facial features, defined in MPEG-4 standard, and used to recognize user’s simple emotions. User presence, head movements , and simple emotions are used to create simple emphatic user interface. In this paper we present our results already used in some application projects for virtual museums.Item Computation and visualization of fabrication artifacts(Václav Skala - UNION Agency, 2009) Malik, Muhammad Muddassir; Heinzl, Christoph; Gröller, Eduard M.; Skala, VáclavThis paper proposes a novel technique to measure fabrication artifacts through direct comparison of a reference surface model with the corresponding industrial CT volume. Our technique uses the information from the surface model to locate corresponding points in the CT dataset. We then compute various comparison metrics to measure differences (fabrication artifacts) between the two datasets. The differences are presented to the user both visually as well as quantitatively. Our comparison techniques are divided into two groups, namely geometry-driven comparison techniques and visual-driven comparison techniques. The geometry-driven techniques provide an overview, while the visual-driven techniques can be used for a localized examination.Item Algebraic 3D reconstruction of planetary nebulae(Václav Skala - UNION Agency, 2009) Wenger, Stephan; Fernández, Juan Aja; Morisset, Christopher; Magnor, Marcus; Skala, VáclavDistant astrophysical objects like planetary nebulae can normally only be observed from a single point of view. Assuming a cylindrically symmetric geometry, one can nevertheless create 3D models of those objects using tomographic methods. We solve the resulting algebraic equations efficiently on graphics hardware. Small deviations from axial symmetry are then corrected using heuristic methods, because the arising 3D models are, in general, no longer unambiguously defined. We visualize the models using real-time volume rendering. Models for actual planetary nebulae created by this approach match the observational data acquired from the earth’s viewpoint, while also looking plausible from other viewpoints for which no experimental data is available.Item An improved technique for full spectral rendering(Václav Skala - UNION Agency, 2009) Radziszewski, Michal; Boryczko, Krzysztof; Alda, Witold; Skala, VáclavIn this paper we present an improved approach to full spectral rendering. The technique is optimized for quasi-Monte Carlo ray tracing, however the underlying physical theory can be applied to any global illumination scheme. We start with explanation of the necessity of full spectral rendering in any correct global illumination system. Then we present, step by step, a rendering scheme using full spectrum simulation. First, we give details on a random point sampling as a method of representing spectra, then we introduce improved spectral sampling technique, designed to reduce variance of image of wavelength dependent phenomena, and finally we show how to integrate the novel sampling technique with selected ray tracing algorithms.Item Giga-voxel rendering from compressed data on a display wall(Václav Skala - UNION Agency, 2009) Parys, R.; Knittel, G.; Skala, VáclavWe present a parallel system capable of rendering multi-gigabyte data sets on a multi-megapixel display wall at interactive rates. The system is based on Residual Vector Quantization which allows us to render extremely large data sets out of the graphics memory. At 0.75 bits per voxel, such large data sets can even be kept on a consumerlevel graphics card. As an example we compress the whole full color “Visible Human Female” data set, approximately 21GByte in size, down to 700MByte. Taking advantage of the fixed code length and the extremely simple decompression scheme of RVQ, all decompression is done on the GPU at very high rates. For each frame the data set is decompressed into small subvolumes which are rendered front to back. Classification and shading can be moved into the decompression step, speeding up the rendering pass.Item Dynamic virtual textures(Václav Skala - UNION Agency, 2009) Taibo, Javier; Seoane, Antonio; Hernández, Luis; Skala, VáclavThe real-time rendering of arbitrarily large textures is a problem that has long been studied in terrain visualization. For years, different approaches have been published that have either expensive hardware requirements or other severe limitations in quality, performance or versatility. The biggest problem is usually a strong coupling between geometry and texture, both regarding database structure, as well as LOD management. This paper presents a new approach to high resolution, real-time texturing of dynamic data that avoids the drawbacks of previous techniques and offers additional possibilities. The most important benefits are: out-of-core texture visualization from dynamic data, efficient per-fragment texture LOD computation, total independence from the geometry engine, high quality filtering and easiness of integration with user custom shaders and multitexturing. Because of its versatility and independence from geometry, the proposed technique can be easily and efficiently applied to any existing terrain geometry engine in a transparent way.
