Number 2 (2012)
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Item Error Metrics for Smart Image Refinement(Václav Skala - UNION Agency, 2012) Amann, Julian; Chajdas, Matthäus G.; Westermann, Rüdiger; Skala, VáclavScanline rasterization is still the dominating approach in real-time rendering. For performance reasons, realtime ray tracing is only used in special applications. However, ray tracing computes better shadows, reflections, refractions, depth-of-field and various other visual effects, which are hard to achieve with a scanline rasterizer. A hybrid rendering approach benefits from the high performance of a rasterizer and the quality of a ray tracer. In this work, a GPU-based hybrid rasterization and ray tracing system that supports reflections, depth-of-field and shadows is introduced. The system estimates the quality improvement that a ray tracer could achieve in comparison to a rasterization based approach. Afterwards, regions of the rasterized image with a high estimated quality improvement index are refined by ray tracing.
Item An applied approach for real-time level-of-detail woven fabric rendering(Václav Skala - UNION Agency, 2012) Yuen, Wallace; Wünsche, Burkhard C.; Holmberg, Nathan; Skala, VáclavPhotorealistic rendering of fabric is essential in many applications ranging from movie special effects to ecommerce and fashion design. Existing techniques usually render the fabric’s microscale structure. However, this can result in severe aliasing and is unsuitable for interactive cloth simulation and manipulation. In this paper we describe a novel real-time level-of-detail fabric rendering technique. The algorithm adjusts geometry and texture details with changing viewpoint by using a mipmapping approach, in order to obtain a perceptually consistent representation on the screen. Compared to previous work we also introduce more parameters allowing the simulation of a wider range of fabrics. Our evaluation demonstrates that the presented approach results in realistic renderings, increases the shader’s run-time speed, and reduces aliasing artifacts by hiding the underlying yarn geometry.Item Multi-view random fields and street-side imagery(Václav Skala - UNION Agency, 2012) Recky, Michal; Leberl, Franz; Ferko, Andrej; Skala, VáclavIn this paper, we present a method that introduces graphical models into a multi-view scenario. We focus on a popular Random Fields concept that many researchers use to describe context in a single image and introduce a new model that can transfer context directly between matched images – Multi-View Random Fields. This method allows sharing not only visual information between images, but also contextual information for the purpose of object recognition and classification. We describe the mathematical model for this method as well as present the application for a domain of street-side image datasets. In this application, the detection of façade elements has improved by up to 20% using Multi-view Random Fields.Item A survey on methods for omnidirectional shadow rendering(Václav Skala - UNION Agency, 2012) Navrátil, Jan; Kobrtek, Jozef; Zemčík, Pavel; Skala, VáclavThis paper focuses on methods of rendering shadows cast by point light sources. The goal is to summarize advantages and disadvantages of methods based on shadow mapping. We compare the traditional approach that exploits cube maps with the Dual–Paraboloid mapping. All of the methods are implemented on the latest hardware and they exploit capabilities of current GPUs. We also implemented optimization techniques which decrease the computational time. We examine the time the methods spent in particular rendering passes and we evaluate their overall performance. Finally, we conclude the comparison with some recommendations for typical applications in which the methods of interest can be exploited. We also suggest some direction of future investigation.Item Design and analysis of visualization techniques for mobile robotics development(Václav Skala - UNION Agency, 2012) Kozlov, Alex; MacDonald, Bruce A.; Wünsche, Burkhard C.; Skala, VáclavSimultaneous localization and mapping (SLAM) algorithms are of vital importance in mobile robotics. This paper presents novel Augmented Reality (AR) visualization techniques for SLAM algorithms, with the purpose of assisting algorithm development. We identify important algorithm invariants and parameters and combine research in uncertainty visualization and AR, to develop novel AR visualizations, which offer an effective perceptual and cognitive overlap for the observation of SLAM systems. A usability evaluation compares the new techniques with the state-of-the-art inferred from the SLAM literature. Results indicate that the novel correlation and color-mapping visualization techniques are preferred by users and more effective for algorithm observation. Furthermore the AR view is preferred over the non-AR view, while being at least similarly effective. Since the visualizations are based on general algorithm properties, the results can be transferred to other applications using the same class of algorithms, such as Particle Filters.Item Color preserving HDR fusion for dynamic scenes(Václav Skala - UNION Agency, 2012) Karadağ, Gökdeniz; Akyüz, Ahmet Oğuz; Skala, VáclavWe present a novel algorithm to efficiently generate high quality high dynamic range (HDR) images. Our method is based on the idea of expanding the dynamic range of a reference image at granularity of tiles. In each tile, we use data from a single exposure, but different tiles can come from different exposures. We show that this approach is not only efficient and robust against camera and object movement, but also improves the color quality of the resulting HDR images. We compare our method against the commonly used HDR generation algorithms.Item Timeseriespaths: projection-based explorative analysis of multivarate time series data(Václav Skala - UNION Agency, 2012) Bernard, Jürgen; Nils, Wilhelm; Scherer, Maximilian; May, Thorsten; Schreck, Tobias; Skala, VáclavThe analysis of time-dependent data is an important problem in many application domains, and interactive visual- ization of time-series data can help in understanding patterns in large time series data. Many effective approaches already exist for visual analysis of univariate time series supporting tasks such as assessment of data quality, detec- tion of outliers, or identification of periodically or frequently occurring patterns. However, much fewer approaches exist which support multivariate time series. The existence of multiple values per time stamp makes the analysis task per se harder, and existing visualization techniques often do not scale well. We introduce an approach for visual analysis of large multivariate time-dependent data, based on the idea of projecting multivariate measurements to a 2D display, visualizing the time dimension by trajectories. We use visual data aggregation metaphors based on grouping of similar data elements to scale with multivariate time series. Aggregation procedures can either be based on statistical properties of the data or on data clustering routines. Appropriately defined user controls allow to navigate and explore the data and interactively steer the parameters of the data aggregation to enhance data analysis. We present an implementation of our approach and apply it on a comprehensive data set from the field of earth observation, demonstrating the applicability and usefulness of our approach.Item Collision detection on point clouds using a 2.5+D image-based approach(Václav Skala - UNION Agency, 2012) dos Anjos, Rafael Kuffner; Pereira, João Madeiras; Oliveira, João Fradinho; Skala, VáclavThis work explores an alternative approach to the problem of collision detection using images instead of geometry to represent complex polygonal environments and buildings derived from laser scan data, used in an interactive navigation scenario. In a preprocessing step, models that are not point clouds, are sampled to create representative point clouds. Our algorithm then creates several 2.5+D maps in a given volume that stacked together form a 3D section of the world. We show that our new representation allows for realistic and fast collision queries with complex geometry such as stairs and that the algorithm is insensitive to the size of the input point cloud at run-time.Item Real-time volume rendering and tractography visualization on the web(Václav Skala - UNION Agency, 2012) Congote, John; Novo, Esther; Kabongo, Luis; Ginsburg, Dan; Gerhard, Stephan; Pienaar, Rudolph; Ruiz, Oscar E.; Skala, VáclavIn the field of computer graphics, Volume Rendering techniques allow the visualization of 3D datasets, and specifically, Volume Ray-Casting renders images from volumetric datasets, typically used in some scientific areas, such as medical imaging. This article aims to describe the development of a combined visualization of tractography and volume rendering of brain T1 MRI images in an integrated way. An innovative web viewer for interactive visualization of neuro-imaging data has been developed based on WebGL. This recently developed standard enables the clients to use the web viewer on a wide range of devices, with the only requirement of a compliant web-browser. As the majority of the rendering tasks take place in the client machine, the effect of bottlenecks and server overloading are minimized. The web application presented is able to compete with desktop tools, even supporting high graphical demands and facing challenges regarding performance and scalability. The developed software modules are available as open source code and include MRI volume data and tractography generated by the Diffusion Toolkit, and connectivity data from the Connectome Mapping Toolkit. Our contribution for the Volume Web Viewer implements early ray termination step according to the tractography depthmap, combining volume images and estimated white matter fibers. Furthermore, the depthmap system extension can be used for visualization of other types of data, where geometric and volume elements are displayed simultaneously.
