VMV: Vision, Modeling, and Visualization

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Cost-effective Feature Enhancement for Volume Datasets
(The Eurographics Association, 2010) Díaz, Jose; Marco, Jordi; Vázquez, Pere-Pau; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Volume models often show high complexity. Local details and overall shape may sometimes be difficult to perceive. Unsharp masking techniques improve the perception of those small features by increasing the local contrast. In this paper we present a simple and fast method for feature enhancement based on 3D mipmaps. In contrast to other approaches, in addition to increasing luminance on the feature details, we also darken the valleys of the volume thus increasing local contrast and making neighboring details more visible. Our approach is fast and simple, with small memory requirements thanks to the use of 3D mipmaps. We also propose a color selection strategy, based on harmonic colors, that further enhances the salient features without abrupt or uncomfortable color changes.
Convex Relaxation for Grain Segmentation at Atomic Scale
(The Eurographics Association, 2010) Boerdgen, Markus; Berkels, Benjamin; Rumpf, Martin; Cremers, Daniel; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Grains are material regions with different lattice orientation at atomic scale. They can be resolved on material surfaces with recent image acquisition technology. Simultaneously, new microscopic simulation tools allow to study mechanical models of grain structures. The robust and reliable identification and visualization of grain boundaries - in images both from simulation and from experiments - is of central importance in the field of material surface analysis. In this work, we compare a variety of variational approaches for grain boundary estimation from microscopy and simulation images. In particular, we show that grain boundary estimation can be solved by means of recently introduced convex relaxation techniques. These techniques allow to compute global solutions or solutions within a known bound of the optimum. Moreover, experimental results both on simulated and on transmission electron microscopy images confirm that the convex relaxation techniques provide significant improvements of the estimated grain boundaries over previously employed multiphase level set formulations.
Adaptive Image-space Stereo View Synthesis
(The Eurographics Association, 2010) Didyk, Piotr; Ritschel, Tobias; Eisemann, Elmar; Myszkowski, Karol; Seidel, Hans-Peter; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Stereo vision is becoming increasingly popular in feature films, visualization and interactive applications such as computer games. However, computation costs are doubled when rendering an individual image for each eye. In this work, we propose to only render a single image, together with a depth buffer and use image-based techniques to generate two individual images for the left and right eye. The resulting method computes a high-quality stereo pair for roughly half the cost of the traditional methods. We achieve this result via an adaptive-grid warping that also involves information from previous frames to avoid artifacts.
Massively Parallel Multiclass Object Recognition
(The Eurographics Association, 2010) Sedding, Helmut; Deger, Ferdinand; Dammertz, Holger; Bouecke, Jan; Lensch, Hendrik P. A.; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
We present a massively parallel object recognition system based on a cortex-like structure. Due to its nature, this general, biologically motivated system can be parallelized efficiently on recent many-core graphics processing units (GPU). By implementing the entire pipeline on the GPU, by rigorously optimizing memory bandwidth and by minimizing branch divergence, we achieve significant speedup compared to both recent CPU as well as GPU implementations for reasonably sized feature dictionaries. We demonstrate an interactive application even on a less powerful laptop which is able to classify webcam images and to learn novel categories in real time.
Visual Analysis of Multivariate Movement Data using Interactive Difference Views
(The Eurographics Association, 2010) Lampe, Ove Daae; Kehrer, Johannes; Hauser, Helwig; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Movement data consisting of a large number of spatio-temporal agent trajectories is challenging to visualize, especially when all trajectories are attributed with multiple variates. In this paper, we demonstrate the visual exploration of such movement data through the concept of interactive difference views. By reconfiguring the difference views in a fast and flexible way, we enable temporal trend discovery. We are able to analyze large amounts of such movement data through the use of a frequency-based visualization based on kernel density estimates (KDE), where it is also possible to quantify differences in terms of the units of the visualized data. Using the proposed techniques, we show how the user can produce quantifiable movement differences and compare different categorical attributes (such as weekdays, ship-type, or the general wind direction), or a range of a quantitative attribute (such as how two hours' traffic compares to the average). We present results from the exploration of vessel movement data from the Norwegian Coastal Administration, collected by the Automatic Identification System (AIS) coastal tracking. There are many interacting patterns in such movement data, both temporal and other more intricate, such as weather conditions, wave heights, or sunlight. In this work we study these movement patterns, answering specific questions posed by Norwegian Coastal Administration on potential shipping lane optimizations.
Instant Texture Synthesis by Numbers
(The Eurographics Association, 2010) Busto, Pau Panareda; Eisenacher, Christian; Lefebvre, Sylvain; Stamminger, Marc; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Appearance Space Texture Synthesis (ASTS) provides fast texture synthesis by example. Unfortunately, speed is only achieved at the cost of a long pre-processing step. This is tedious for artists and limits the input resolution. In addition, the aggressively pruned search space results in strong artifacts when synthesizing multiple textures under user guidance (Texture-By-Numbers, TBN). In this paper, we replace the k-coherence search step used by most modern synthesis algorithms with a new parallel, coherent random walk. We show that this drastically improves the synthesis quality with TBN, while maintaining the parallel nature, speed, and flexibility of the original ASTS runtime. Since it removes the expensive pre-computation of k-coherent candidates, we are able to use larger inputs, and start synthesis much faster. This is essential for artists designing high-quality exemplars.
Dynamic Focus + Context for Volume Rendering
(The Eurographics Association, 2010) Sikachev, Peter; Rautek, Peter; Bruckner, Stefan; Gröller, M. Eduard; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Interactive visualization is widely used in many applications for efficient representation of complex data. Many techniques make use of the focus+context approach in a static manner. These techniques do not fully make use of the interaction semantics. In this paper we present a dynamic focus+context approach that highlights salient features during user interaction. We explore rotation, panning, and zooming interaction semantics and propose several methods of changing visual representations, based on a suggested engagement-estimation method. We use DVR-MIP interpolation and a radial opacity-change approach, exploring rotation, panning, and zooming semantics. Our approach adds short animations during user interaction that help to explore the data efficiently and aid the user in the detection of unknown features.
Feature Preserving Sketching of Volume Data
(The Eurographics Association, 2010) Kerber, Jens; Bokeloh, Martin; Wand, Michael; Krüger, Jens; Seidel, Hans-Peter; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
In this paper, we present a novel method for extracting feature lines from volume data sets. This leads to a reduction of visual complexity and provides an abstraction of the original data to important structural features. We employ a new iteratively reweighted least-squares approach that allows us to detect sharp creases and to preserve important features such as corners or intersection of feature lines accurately. Traditional least-squares methods This is important for both visual quality as well as reliable further processing in feature detection algorithms. Our algorithm is efficient and easy to implement, and nevertheless effective and robust to noise. We show results for a number of different data sets.
Image-Error-Based Level of Detail for Landscape Visualization
(The Eurographics Association, 2010) Clasen, Malte; Prohaska, Steffen; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
We present a quasi-continuous level of detail method that is based on an image error metric to minimize the visual error. The method is designed for objects of high geometric complexity such as trees. By successive simplifications, it constructs a level of detail hierarchy of unconnected primitives (ellipsoids, lines) to approximate the input models at increasingly coarser levels. The hierarchy is constructed automatically without manual intervention. When rendering roughly 100k model instances at a low visual error compared to rendering the full resolution model, our method is two times faster than billboard clouds.
Continuous Deformations of Implicit Surfaces
(The Eurographics Association, 2010) Esturo, Janick Martinez; Rössl, Christian; Theisel, Holger; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
We introduce an approach for the continuous deformation of implicit surfaces which considers properties of all isosurfaces of a volume data set simultaneously. This is achieved by integrating divergence-free vector fields which is carried out by an efficient backward Lagrangian integration scheme. Our deformation guarantees volume preservation inside each isosurface as well as the preservation of continuity and topology of every isosurface. For visualization and interaction, we offer a real-time mode that allows interactive working on the resolution of the underlying volumetric grid as well as a grid resolution independent mode offering exact extraction of arbitrary isosurfaces. We apply the approach to the deformation of measured volume data sets as well as to the design of complex implicit shapes with a simple pre-defined topology.
CALTag: High Precision Fiducial Markers for Camera Calibration
(The Eurographics Association, 2010) Atcheson, Bradley; Heide, Felix; Heidrich, Wolfgang; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
We present a self-identifying marker pattern for camera calibration, together with the associated detection algorithm. The pattern is designed to support high-precision, fully-automatic localization of calibration points, as well as identification of individual markers in the presence of significant occlusions, uneven illumination, and observations under extremely acute angles. The detection algorithm is efficient and free of parameters. After calibration we obtain reprojection errors significantly lower than with state-of-the art self-identifying reference patterns.
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-Salama
Procedural 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.
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-Salama
We 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.
Ultrasound Painting of Liver Vascular Tree
(The Eurographics Association, 2010) Birkeland, Asmund; Viola, Ivan; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
In 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.
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-Salama
This 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.
Geometric Reconstruction of the Ostium of Cerebral Aneurysms
(The Eurographics Association, 2010) Neugebauer, Mathias; Diehl, Volker; Skalej, Martin; Preim, Bernhard; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Polygonal 3D-reconstructions of cerebral aneurysms, combined with simulated or measured flow data provide important information for medical research, risk assessment and therapy planning. Landmarks, orientation axis, and a subdivision into functional unities, support the purposeful exploration of this complex data. The ostium, the area of inflow into the aneurysm, is the reference structure for various landmarks, axis and the initial subdivision into aneurysm's body and parent vessel.We present an approach to automatically extract important landmarks and geometrically reconstruct the ostium. Our method was successfully applied to various types of saccular aneurysms. These results were discussed with radiology experts. Our approach was considered as useful to reduce interpersonal variance in the ostium determination and forms a basis for subsequent quantification and exploration.
Proxy-Guided Texture Synthesis for Rendering Natural Scenes
(The Eurographics Association, 2010) Bonneel, Nicolas; Panne, Michiel van de; Lefebvre, Sylvain; Drettakis, George; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Landscapes and other natural scenes are easy to photograph but difficult to model and render. We present a proxy-guided pipeline which allows for simple 3D proxy geometry to be rendered with the rich visual detail found in a suitably pre-annotated example image. This greatly simplifies the geometric modeling and texture mapping of such scenes. Our method renders at near-interactive rates and is designed by carefully adapting guidancebased texture synthesis to our goals. A guidance-map synthesis step is used to obtain silhouettes and borders that have the same rich detail as the source photo, using a Chamfer distance metric as a principled way of dealing with discrete texture labels. We adapt an efficient parallel approach to the challenging guided synthesis step we require, providing a fast and scalable solution. We provide a solution for local temporal coherence, by introducing a reprojection algorithm, which reuses earlier synthesis results when feasible, as measured by a distortion metric. Our method allows for the consistent integration of standard CG elements with the texture-synthesized elements. We demonstrate near-interactive camera motion and landscape editing on a number of examples.
The Minimal Bounding Volume Hierarchy
(The Eurographics Association, 2010) Bauszat, Pablo; Eisemann, Martin; Magnor, Marcus; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Bounding volume hierarchies (BVH) are a commonly used method for speeding up ray tracing. Even though the memory footprint of a BVH is relatively low compared to other acceleration data structures, they still can consume a large amount of memory for complex scenes and exceed the memory bounds of the host system. This can lead to a tremendous performance decrease on the order of several magnitudes. In this paper we present a novel scheme for construction and storage of BVHs that can reduce the memory consumption to less than 1% of a standard BVH. We show that our representation, which uses only 2 bits per node, is the smallest possible representation on a per node basis that does not produce empty space deadlocks. Our data structure, called the Minimal Bounding Volume Hierarchy (MVH) reduces the memory requirements in two important ways: using implicit indexing and preset surface reduction factors. Obviously, this scheme has a non-negligible computational overhead, but this overhead can be compensated to a large degree by shooting larger ray bundles instead of single rays, using a simpler intersection scheme and a two-level representation of the hierarchy. These measure enable interactive ray tracing performance without the necessity to rely on out-of-core techniques that would be inevitable for a standard BVH.
Relighting Spherical Light Fields with Polynomial Texture Mapping
(The Eurographics Association, 2010) Brückbauer, Lisa; Rezk-Salama, Christof; Kolb, Andreas; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
We present a novel image-based rendering (IBR) technique based on spherical light fields, which makes it possible to relight the captured object for arbitrary viewing positions. This approach incorporates view-dependent effects such as self-shadowing and inter-reflections. For this, we apply Polynomial Texture Maps (PTMs) to 3D objects. Once acquired, a light field representation of an object can be relit at low computation costs due to the efficiency of the PTM approach. The relighting process makes even small lighting changes visible and retains surface appearance even on a meso-scale level. Furthermore, we present a simple method to adopt specular reflections captured in the PTM to novel viewing directions.
QEM-Filtering: A New Technique for Feature-Sensitive Terrain Mesh Simplification
(The Eurographics Association, 2010) Löffler, Falko; Schumann, Heidrun; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Terrain simplification generates multi-resolution models, from which - traditionally - irregular or semi-regular triangulations are extracted to render a terrain at a suitable level of detail. Recent terrain simplification techniques, in contrast, rely on GPU-friendly regular grids and generate multiple resolutions by applying the filtering and sub-sampling paradigm. However, due to the smoothing and uniform sampling, these techniques sparsely approximate the terrain surface. Consequently, in order to guarantee a certain error threshold, considerably more triangles need to be rendered. In this paper, we present a novel feature-sensitive simplification technique. Our approach follows the aforementioned paradigm. The key idea is to maintain the regularity while recomputing the vertex positions by taking a specific error metric into account, namely the quadric error metric (QEM). Compared to previous approaches, we apply the paradigm to the grid of vertex-associated quadrics. From these we extract vertices of the new resolution by relying on quadric error minimization. We, thus, maintain the regular grid structure while preserving terrain features. Compared to methods, which are solely based on vertex-filtering and sub-sampling, our approach reduces the approximation error. As a consequence, we require fewer triangles, which improves the rendering performance.

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