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Item Application of Tensor Approximation to Multiscale Volume Feature Representations(The Eurographics Association, 2010) Suter, Susanne K.; Zollikofer, Christoph P. E.; Pajarola, Renato; Reinhard Koch and Andreas Kolb and Christof Rezk-SalamaAdvanced 3D microstructural analysis in natural sciences and engineering depends ever more on modern data acquisition and imaging technologies such as micro-computed or synchrotron tomography and interactive visualization. The acquired volume data sets are not only of high-resolution but in particular exhibit complex spatial structures at different levels of scale (e.g. variable spatial expression of multiscale periodic growth structures in tooth enamel). Such highly structured volume data sets represent a tough challenge to be analyzed and explored by means of interactive visualization due to the amount of raw volume data to be processed and filtered for the desired features. As an approach to address this bottleneck by multiscale feature preserving data reduction, we propose higher-order tensor approximations (TAs). We demonstrate the power of TA to represent, and highlight the structural features in volume data. We visually and quantitatively show that TA yields high data reduction and that TA preserves volume features at multiple scales.Item Graphical Interface Models for Procedural Mesh Growing(The Eurographics Association, 2010) Menz, Stefan; Dammertz, Holger; Hanika, Johannes; Weber, Michael; Lensch, Hendrik P. A.; Reinhard Koch and Andreas Kolb and Christof Rezk-SalamaProcedural modeling allows to create highly complex 3D scenes from a small set of construction rules, which has several advantages over storing the full data of an object. The most important ones are a very small memory footprint and the ability to generate infinite variations of one prototype object by using the same set of rules. However, the problem that procedural modeling imposes on the user is to define a reasonable set of rules to generate a specific object. To simplify this task, we present new interaction metaphors for a graphical user interface and a minimal set of geometric operations that allow the user to efficiently create such rules and the respective models. These metaphors are then implemented in a prototype system and are evaluated by user tests with regard to usability and user performance. The results show that the system enables even inexperienced users to create complex 3D objects via procedural modeling using the presented approach.Item Interactive Multi-View Facade Image Editing(The Eurographics Association, 2010) Musialski, Przemyslaw; Luksch, Christian; Schwärzler, Michael; Buchetics, Matthias; Maierhofer, Stefan; Purgathofer, Werner; Reinhard Koch and Andreas Kolb and Christof Rezk-SalamaWe propose a system for generating high-quality approximated façade ortho-textures based on a set of perspective source photographs taken by a consumer hand-held camera. Our approach is to sample a combined orthographic approximation over the facade-plane from the input photos. In order to avoid kinks and seams which may occur on transitions between different source images, we introduce color adjustment and gradient domain stitching by solving a Poisson equation in real-time. In order to add maximum control on the one hand and easy interaction on the other, we provide several editing interactions allowing for user-guided post-processing.Item Geometry-aware Video Registration(The Eurographics Association, 2010) Palma, Gianpalo; Callieri, Marco; Dellepiane, Matteo; Corsini, Massimiliano; Scopigno, Roberto; Reinhard Koch and Andreas Kolb and Christof Rezk-SalamaWe present a new method for the accurate registration of video sequences of a real object over its dense triangular mesh. The goal is to obtain an accurate video-to-geometry registration to allow the bidirectional data transfer between the 3D model and the video using the perspective projection defined by the camera model. Our solution uses two different approaches: feature-based registration by KLT video tracking, and statistic-based registration by maximizing the Mutual Information (MI) between the gradient of the frame and the gradient of the rendering of the 3D model with some illumination related properties, such as surface normals and ambient occlusion. While the first approach allows a fast registration of short sequences with simple camera movements, the MI is used to correct the drift problem that KLT tracker produces over long sequences, due to the incremental tracking and the camera motion. We demonstrate, using synthetic sequences, that the alignment error obtained with our method is smaller than the one introduced by KLT, and we show the results of some interesting and challenging real sequences of objects of different sizes, acquired under different conditions.Item Ultrasound Painting of Liver Vascular Tree(The Eurographics Association, 2010) Birkeland, Asmund; Viola, Ivan; Reinhard Koch and Andreas Kolb and Christof Rezk-SalamaIn treatment planning and surgical interventions, physicians and surgeons need information about the spatial extent of specific features and the surrounding structures. Previous techniques for extracting features, based on magnetic resonance imaging and computed tomography scans, can be slow and cumbersome and are rarely used by doctors. In this paper we will present a novel approach to extract features from tracked 2D ultrasound, in particular hypo-echoic regions such as blood vessels. Features are extracted during live examinations, removing the need for slow and cumbersome post-scan processes and interaction is based on the natural interaction techniques used by doctors during the examination. The ultrasound probe is utilized as a 3D brush, painting features in a 3D environment. The painting occurs during a regular examination, producing little extra interaction from the doctor. We will introduce a novel approach to extract hypo-echoic regions from an ultrasound image and track the regions from frame to frame. 3D models are then generated by storing the outline of the region as a 3D point cloud. Automatically detecting branching, this technique can handle complex structures, such as liver vessel trees, and track multiple regions simultaneously. During the examination, the point cloud is triangulated in real-time, enabling the doctor to examine the results live and discard areas which are unsatisfactory. To enable modifications of the extracted 3D models, we present how the ultrasound probe can be used as a interaction tool for fast point cloud editing.Item Pixel-Based Hyperparameter Selection for Feature-Based Image Registration(The Eurographics Association, 2010) Brunet, Florent; Bartoli, Adrien; Navab, Nassir; Malgouyres, Rémy; Reinhard Koch and Andreas Kolb and Christof Rezk-SalamaThis paper deals with parametric image registration from point correspondences in deformable environments. In this problem, it is essential to determine correct values for hyperparameters such as the number of control points of the warp, a smoothing parameter weighting a term in the cost function, or an M-estimator threshold. This is usually carried out either manually by a trial-and-error procedure or automatically by optimizing a criterion such as the Cross-Validation score. In this paper, we propose a new criterion that makes use of all the available image photometric information. We use the point correspondences as a training set to determine the warp parameters and the photometric information as a test set to tune the hyperparameters. Our approach is fully robust in the sense that it copes with both erroneous point correspondences and outliers in the images caused by, for instance, occlusions or specularities.Item Coherent Background Video Inpainting through Kalman Smoothing along Trajectories(The Eurographics Association, 2010) Bugeau, Aurélie; Gargallo, Paul; D'Hondt, Olivier; Hervieu, Alexandre; Papadakis, Nicolas; Caselles, Vicent; Reinhard Koch and Andreas Kolb and Christof Rezk-SalamaVideo inpainting consists in recovering the missing or corrupted parts of an image sequence so that the reconstructed sequence looks natural. For each frame, the reconstruction has to be spatially coherent with the rest of the image and temporally with respect to the reconstructions of adjacent frames. Most of existing methods only focus on inpainting foreground objects moving with a periodic motion and consider that the background is almost static. In this paper we address the problem of background inpainting and propose a method that handles dynamic background (illumination changes, moving camera, dynamic textures...). The algorithm starts by applying an image inpainting technique to each frame of the sequence and then temporally smoothes these reconstructions through Kalman smoothing along the estimated trajectories of the unknown points. The computation of the trajectories relies on the estimation of forward and backward dense optical flow fields. Several experiments and comparisons demonstrate the performance of the proposed approach.Item Evaluation of Geometric Registration Methods for Using Spatial Augmented Reality in the Automotive Industry(The Eurographics Association, 2010) Menk, Christoffer; Jundt, Eduard; Koch, Reinhard; Reinhard Koch and Andreas Kolb and Christof Rezk-SalamaSpatial augmented reality is especially interesting for the automotive industry, because in the production process of a car a lot of virtual content and also real objects are used. Therefore, the virtual content can be directly projected onto the real object to combine the advantages of the real and virtual world. One important issue for the usage of spatial augmented reality in automotive processes and applications is that the virtual content has to be projected with a very high accuracy onto the real object, because decisions are made on the basis of the projection. Therefore, we present in this article a new method for the evaluation of geometric registration techniques which align a projector to a real object. Additionally, we use this proposed method to evaluate existing geometric registration techniques. Furthermore, we present a new application where a projector is used to support the design process of a new car.Item Direct Resampling for Isotropic Surface Remeshing(The Eurographics Association, 2010) Fuhrmann, Simon; Ackermann, Jens; Kalbe, Thomas; Goesele, Michael; Reinhard Koch and Andreas Kolb and Christof Rezk-SalamaWe present a feature-sensitive remeshing algorithm for relaxation-based methods. The first stage of the algorithm creates a new mesh from scratch by resampling the reference mesh with an exact vertex budget with either uniform or non-uniform vertex distribution according to a density function. The newly introduced samples on the mesh surface are triangulated directly in 3D by constructing a mutual tessellation. The second stage of the algorithm optimizes the positions of the mesh vertices by building a weighted centroidal Voronoi tessellation to obtain a precise isotropic placement of the samples. We achieve isotropy by employing Lloyd's relaxation method, but other relaxation schemes are applicable. The proposed algorithm handles diverse meshes of arbitrary genus and guarantees that the remeshed model has the same topology as the input mesh. The density function can be defined by the user or derived automatically from the estimated curvature at the mesh vertices. A subset of the mesh edges may be tagged as sharp features to preserve the characteristic appearance of technical models. The new method can be applied to large meshes and produces results faster than previously achievable.Item DC-Splines: Revisiting the Trilinear Interpolation on the Body-Centered Cubic Lattice(The Eurographics Association, 2010) Domonkos, Balázs; Csébfalvi, Balázs; Reinhard Koch and Andreas Kolb and Christof Rezk-SalamaIn this paper, we thoroughly study a trilinear interpolation scheme previously proposed for the Body-Centered Cubic (BCC) lattice. We think that, up to now, this technique has not received the attention that it deserves. By a frequency-domain analysis we show that it can isotropically suppress those aliasing spectra that contribute most to the postaliasing effect. Furthermore, we present an efficient GPU implementation, which requires only six trilinear texture fetches per sample. Overall, we demonstrate that the trilinear interpolation on the BCC lattice is competitive to the linear box-spline interpolation in terms of both efficiency and image quality. As a generalization to higher-order reconstruction, we introduce DC-splines that are constructed by convolving a Discrete filter with a Continuous filter, and easy to adapt to the Face-Centered Cubic (FCC) lattice as well.