VMV13

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https://diglib.eg.org/handle/10.2312/1017

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3D Shape Cropping
(The Eurographics Association, 2013) Franco, Jean-Sebastien; Petit, Benjamin; Boyer, Edmond; Michael Bronstein and Jean Favre and Kai Hormann
We introduce shape cropping as the segmentation of a bounding geometry of an object as observed by sensors with different modalities. Segmenting a bounding volume is a preliminary step in many multi-view vision applications that consider or require the recovery of 3D information, in particular in multi-camera environments. Recent vision systems used to acquire such information often combine sensors of different types, usually color and depth sensors. Given depth and color images we present an efficient geometric algorithm to compute a polyhedral bounding surface that delimits the region in space where the object lies. The resulting cropped geometry eliminates unwanted space regions and enables the initialization of further processes including surface refinements. Our approach exploits the fact that such a region can be defined as the intersection of 3D regions identified as non empty in color or depth images. To this purpose, we propose a novel polyhedron combination algorithm that overcomes computational and robustness issues exhibited by traditional intersection tools in our context. We show the correction and effectiveness of the approach on various combination of inputs.
Adaptive Surface Visualization of Vessels with Embedded Blood Flow Based on the Suggestive Contour Measure
(The Eurographics Association, 2013) Lawonn, Kai; Gasteiger, Rocco; Preim, Bernhard; Michael Bronstein and Jean Favre and Kai Hormann
The investigation of hemodynamic information for the assessment of cardiovascular diseases (CVD) has increased in recent years. Improved flow measuring modalities and computational fluid dynamics (CFD) simulations are suitable to provide domain experts with reliable blood flow information. For a visual exploration of the flow information domain experts are used to investigate the flow information combined with its enclosed vessel anatomy. Since the flow is spatially embedded in the surrounding vessel surface, occlusion problems have to be resolved that include a meaningful visual reduction of the vessel surface but still provide important anatomical features. We accomplish this by applying an adaptive surface visualization inspired by the suggestive contour measure. Our approach combines several visualization techniques to improve the perception of surface shape and depth. Thereby, we ensure appropriate visibility of the embedded flow information, which can be depicted with established or advanced flow visualization techniques. We apply our approach to cerebral aneurysms and aortas with simulated and measured blood flow. In an informal user feedback with nine domain experts, we confirm the advantages of our approach compared with existent methods, e.g., semi-transparent surface rendering.
Audio Resynthesis on the Dancefloor: A Music Structural Approach
(The Eurographics Association, 2013) Tauscher, Jan-Philipp; Wenger, Stephan; Magnor, Marcus; Michael Bronstein and Jean Favre and Kai Hormann
We propose a method for synthesizing a novel soundtrack from an existing musical piece while preserving its structure and continuity from a music theoretical point of view. Existing approaches analyze a musical piece for possible cut points that allow the resynthesis of a novel soundtrack by lining up the source segments according to specified rules but fail to maintain musically correct song progression. Introducing the alignment of rhythmic and harmonic structures during transition point detection, we employ beat tracking as the analysis core component and take the human sound perception into account. Automatic segment rearrangement is improved by employing a novel belief propagation approach that enables user-defined constraints for the output soundtrack, allowing video editors or dance choreographers to tailor a soundtrack to their specific demands.
Closed-Form Hierarchical Finite Element Models for Part-Based Object Detection
(The Eurographics Association, 2013) Rak, Marko; Engel, Karin; Tönnies, Klaus D.; Michael Bronstein and Jean Favre and Kai Hormann
In this work we address part-based object detection under variability of part shapes and spatial relations. Our approach bases on the hierarchical finite element modeling concept of Engel and Tönnies [ET09a, ET09b]. They model object parts by elastic materials, which adapt to image structures via image-derived forces. Spatial part relations are realized through additional layers of elastic material forming an elastic hierarchy. We present a closed-form solution to this concept, reformulating the hierarchical optimization problem into the optimization of a non-hierarchical finite element model. This allows us to apply standard finite element techniques to hierarchical problems and to provide an efficient framework for part-based object detection. We demonstrate our approach at the example of lumbar column detection in magnetic resonance imaging on a data set of 49 subjects. Given a rough model initialization, our approach solved the detection problem reliably in 45 out of 49 cases, showing computation times of only a few seconds per subject.
Cloth-Fluid Contact
(The Eurographics Association, 2013) Huber, Markus; Eberhardt, Bernhard; Weiskopf, Daniel; Michael Bronstein and Jean Favre and Kai Hormann
We present a robust and efficient method for the two-way coupling between particle-based fluid simulations and infinitesimally thin solids represented by triangular meshes. Our approach is based on a hybrid method that combines a repulsion force approach with a continuous intersection handling to guarantee that no penetration occurs. Moreover, boundary conditions for the tangential component of the fluids velocity are implemented to model the no-slip boundary condition. The proposed method is particularly useful for dynamic surfaces, like cloth and thin shells. In addition, we demonstrate how standard fluid surface reconstruction algorithms can be modified to prevent the calculated surface from intersecting close objects. We have implemented our approach for the bidirectional interaction between liquid simulations based on Smoothed Particle Hydrodynamics (SPH) and standard mesh-based cloth simulation systems.
Datasets and Benchmarks for Densely Sampled 4D Light Fields
(The Eurographics Association, 2013) Wanner, Sven; Meister, Stephan; Goldluecke, Bastian; Michael Bronstein and Jean Favre and Kai Hormann
We present a new benchmark database to compare and evaluate existing and upcoming algorithms which are tailored to light field processing. The data is characterised by a dense sampling of the light fields, which best fits current plenoptic cameras and is a characteristic property not found in current multi-view stereo benchmarks. It allows to treat the disparity space as a continuous space, and enables algorithms based on epipolar plane image analysis without having to refocus first. All datasets provide ground truth depth for at least the center view, while some have additional segmentation data available. Part of the light fields are computer graphics generated, the rest are acquired with a gantry, with ground truth depth established by a previous scanning of the imaged objects using a structured light scanner. In addition, we provide source code for an extensive evaluation of a number of previously published stereo, epipolar plane image analysis and segmentation algorithms on the database.
Dynamic Time Warping Based 3D Contours
(The Eurographics Association, 2013) Croci, Simone; Smolic, Aljoscha; Wang, Oliver; Michael Bronstein and Jean Favre and Kai Hormann
In this work, we present a method for computing 3D contours from the silhouettes of objects in multiple views. Our approach unwraps contours into 1D signals and computes an efficient, globally optimal alignment using a modified dynamic time warping technique. Using our method, we can approximate real model geometry by interpolating the 3D contour on the billboard plane, thereby reducing the stereo problem to 1D and allowing for much more efficient and robust computation methods.
Epipolar Plane Image Refocusing for Improved Depth Estimation and Occlusion Handling
(The Eurographics Association, 2013) Diebold, Maximilian; Goldluecke, Bastian; Michael Bronstein and Jean Favre and Kai Hormann
In contrast to traditional imaging, the higher dimensionality of a light field offers directional information about the captured intensity. This information can be leveraged to estimate the disparity of 3D points in the captured scene. A recent approach to estimate disparities analyzes the structure tensor and evaluates the orientation on epipolar plane images (EPIs). While the resulting disparity maps are generally satisfying, the allowed disparity range is small and occlusion boundaries can become smeared and noisy. In this paper, we first introduce an approach to extend the total allowed disparity range. This allows for example the investigation of camera setups with a larger baseline, like in the Middlebury 3D light fields. Second, we introduce a method to handle the difficulties arising at boundaries between fore- and background objects to achieve sharper edge transitions.
Evaluating the Perceptual Impact of Rendering Techniques on Thematic Color Mappings in 3D Virtual Environments
(The Eurographics Association, 2013) Engel, Juri; Semmo, Amir; Trapp, Matthias; Döllner, Jürgen; Michael Bronstein and Jean Favre and Kai Hormann
Using colors for thematic mapping is a fundamental approach in visualization, and has become essential for 3D virtual environments to effectively communicate multidimensional, thematic information. Preserving depth cues within these environments to emphasize spatial relations between geospatial features remains an important issue. A variety of rendering techniques have been developed to preserve depth cues in 3D information visualization, including shading, global illumination, and image stylization. However, these techniques alter color values, which may lead to ambiguity in a color mapping and loss of information. Depending on the applied rendering techniques and color mapping, this loss should be reduced while still preserving depth cues when communicating thematic information. This paper presents the results of a quantitative and qualitative user study that evaluates the impact of rendering techniques on information and spatial perception when using visualization of thematic data in 3D virtual environments. We report the results of this study with respect to four perception-related tasks, showing significant differences in error rate and task completion time for different rendering techniques and color mappings.
Expressive Spectral Error Visualization for Enhanced Spectral Unmixing
(The Eurographics Association, 2013) Labitzke, Björn; Urrigshardt, Frank; Kolb, Andreas; Michael Bronstein and Jean Favre and Kai Hormann
A major issue in multispectral data analysis stems from the concept of spectral mixture analysis, i.e. the fact that a pixel does not cover only one material but corresponds to a mixture of materials. Even though many automatic methods for spectral unmixing exist, in many practical applications, domain experts have to verify the result and sometimes have to manually adjust the set of determined materials to achieve proper spectral reconstructions. In this paper, we propose an approach to enhance the very tedious and time-consuming task of manual verification of the unmixing and optional refinement of the materials. Our visual analysis approach comprises different techniques for an expressive spectral error visualization, efficiently guiding the user towards spectra in the dataset which are potentially missing materials. Here, combined views allow comprehensive, local and global error inspections in parallel. We present results of our proposed approach for two domains.
Fine-Scale Editing of Continuous Volumes using Adaptive Surfaces
(The Eurographics Association, 2013) Ruhl, Kai; Wenger, Stephan; Franke, Dennis; Saretzki, Julius; Magnor, Marcus; Michael Bronstein and Jean Favre and Kai Hormann
Many fields of science such as astronomy and astrophysics require the visualization and editing of smooth, continuous volume data. However, current high-level approaches to volume editing concentrate on segmentable volume data prevalent in medical or engineering contexts, and therefore rely on the presence of well-defined 3D surface layers. Editing arbitrary volumes, on the other hand, is currently only possible using low-level approaches based on the rather unintuitive direct manipulation of axis-aligned slices. In this paper, we present a technique to add or modify fine-scale structures within astronomical nebulae based on adaptive drawing surfaces that enable 2Dimage- like editing approaches. Our results look more natural and have been produced in a much shorter time than previously possible with axis-aligned slice editing.
Geometric Point Light Source Calibration
(The Eurographics Association, 2013) Ackermann, Jens; Fuhrmann, Simon; Goesele, Michael; Michael Bronstein and Jean Favre and Kai Hormann
We present a light position calibration technique based on a general arrangement of at least two reflective spheres in a single image. Contrary to other techniques we do not directly intersect rays for triangulation but instead solve for the optimal light position by evaluating the image-space error of the light highlights reflected from the spheres. This approach has been very successful in the field of Structure-from-Motion estimation. It has not been applied to light source calibration because determining the reflection point on the sphere to project the highlight back in the image is a challenging problem. We show a solution and define a novel, non-linear error function to recover the position of a point light source. We also introduce a light position estimation that is based on observing the light source directly in multiple images which does not use any reflections. Finally, we evaluate both proposed techniques and the classical ray intersection method in several scenarios with real data.
Illustrative Rendering of Particle Systems
(The Eurographics Association, 2013) Chandler, Jennifer; Obermaier, Harald; Joy, Kenneth I.; Michael Bronstein and Jean Favre and Kai Hormann
Sets of particles are a frequently used tool for the exploration of time-varying flow fields due to their ease of use and conceptual simplicity. Understanding temporal changes in such particle systems can be difficult with traditional visualization methods such as isosurface rendering and particle splatting. These types of methods only show the current shape of the point cloud and give no context about how the current time step relates to previous or future time steps. In this paper we present an illustrative rendering approach to visualizing particle systems. We use illustrative rendering techniques like silhouettes and trajectory arrows combined with volume raycasting to highlight important features in the particle system and show how these features change across time steps. Our method allows users to easily identify structures within the point cloud and understand how they evolve over time.
Image Based Rendering from Perspective and Orthographic Images for Autostereoscopic Multi-View Displays
(The Eurographics Association, 2013) Jung, Daniel; Koch, Reinhard; Michael Bronstein and Jean Favre and Kai Hormann
Current autostereoscopic (AS) multi-view displays for video that are targeted at the market allow typically up to 60 frames per second and offer between 20 and 60 different views per pixel. Future full parallax AS displays may well require thousands of views simultaneously. With the large number of different views video displays consume a huge amount of data, either transferred to the display or to be computed on demand from a 3D scene representation. In the following a novel depth-image based rendering interpolation algorithm targeted at multi-view video displays is introduced that combines the results of an interpolation on orthographic and perspective images. The same idea is further utilised to implement an efficient computer graphic rendering algorithm for full parallax AS displays.
Integrated Multi-aspect Visualization of 3D Fluid Flows
(The Eurographics Association, 2013) Brambilla, Andrea; Andreassen, Øyvind; Hauser, Helwig; Michael Bronstein and Jean Favre and Kai Hormann
The motion of a fluid is affected by several intertwined flow aspects. Analyzing one aspect at a time can only yield partial information about the flow behavior. More details can be revealed by studying their interactions. Our approach enables the investigation of these interactions by simultaneously visualizing meaningful flow aspects, such as swirling motion and shear strain. We adopt the notions of relevance and coherency. Relevance identifies locations where a certain flow aspect is deemed particularly important. The related piece of information is visualized by a specific visual entity, placed at the corresponding location. Coherency instead represents the homogeneity of a flow property in a local neighborhood. It is exploited in order to avoid visual redundancy and to reduce occlusion and cluttering. We have applied our approach to three CFD datasets, obtaining meaningful insights.
Interactive Comparative Visualization of Multimodal Brain Tumor Segmentation Data
(The Eurographics Association, 2013) Lindemann, Florian; Laukamp, Kai; Jacobs, Andreas H.; Hinrichs, Klaus; Michael Bronstein and Jean Favre and Kai Hormann
We present a visualization system for the analysis of multi-modal segmentation data of brain tumors. Our system is designed to allow researchers and doctors a further investigation of segmented tumor data beyond a quantitative assessment of size. This includes the efficient visual analysis of the shape and relative position of the different, often overlapping segmented data modalities, using high quality 3D renderings of the data. Furthermore, our system provides visualization methods to compare tumor segmentation volumes acquired at various points of time, which helps the user to explore changes in shape and size before and after treatment. We also employ two novel interactive diagrams which allow the user to quickly navigate and analyze overlapping tumor regions. All methods are assembled and linked in a multi-view framework.
Interactive Direct Volume Rendering with Many-light Methods and Transmittance Caching
(The Eurographics Association, 2013) Weber, Christoph; Kaplanyan, Anton S.; Stamminger, Marc; Dachsbacher, Carsten; Michael Bronstein and Jean Favre and Kai Hormann
In this paper we present an interactive global illumination method for Direct Volume Rendering (DVR) based on the many-light approach, a class of global illumination methods which gained much interest recently. We extend these methods to handle transfer function and volume density updates efficiently in order to foster ability of interactive volume exploration. Global illumination techniques accounting for all light transport phenomena are typically computationally too expensive for interactive DVR. Many-light methods represent the light transport in a volume by determining a set of virtual light sources whose direct illumination and single scattering to a view ray approximate full global illumination. Our technique reduces computation caused by transfer function changes by recomputing the contribution of these virtual lights, and rescaling or progressively updating their volumetric shadow maps and locations. We discuss these optimizations in the context of DVR and demonstrate their application to interactive rendering.
Level of Detail for Real-Time Volumetric Terrain Rendering
(The Eurographics Association, 2013) Scholz, Manuel; Bender, Jan; Dachsbacher, Carsten; Michael Bronstein and Jean Favre and Kai Hormann
Terrain rendering is an important component of many GIS applications and simulators. Most methods rely on heightmap-based terrain which is simple to acquire and handle, but has limited capabilities for modeling features like caves, steep cliffs, or overhangs. In contrast, volumetric terrain models, e.g. based on isosurfaces can represent arbitrary topology. In this paper, we present a fast, practical and GPU-friendly level of detail algorithm for large scale volumetric terrain that is specifically designed for real-time rendering applications. Our algorithm is based on a longest edge bisection (LEB) scheme. The resulting tetrahedral cells are subdivided into four hexahedra, which form the domain for a subsequent isosurface extraction step. The algorithm can be used with arbitrary volumetric models such as signed distance fields, which can be generated from triangle meshes or discrete volume data sets. In contrast to previous methods our algorithm does not require any stitching between detail levels. It generates crack free surfaces with a good triangle quality. Furthermore, we efficiently extract the geometry at runtime and require no preprocessing, which allows us to render infinite procedural content with low memory consumption.
Local Extraction of Bifurcation Lines
(The Eurographics Association, 2013) Machado, Gustavo M.; Sadlo, Filip; Ertl, Thomas; Michael Bronstein and Jean Favre and Kai Hormann
We present local extraction of bifurcation lines together with extraction of their manifolds, a topological feature that has not yet been sufficiently recognized in scientific visualization. The bifurcation lines are extracted by a modification of the vortex core line extraction techniques due to Sujudi-Haimes, and Roth-Peikert, both formulated using the parallel vectors operator. While the former provides acceptable results only in configurations with high hyperbolicity and low curvature of the bifurcation lines, the latter operates only well in configurations with low hyperbolicity but is able to perform well with strong curvature of the bifurcation lines, however, with the drawback that it often fails to provide a solution. We present refinement of the solutions of the parallel vectors operator as a means to improve both criteria and, in particular, to refine the solutions of the Sujudi-Haimes criterion in cases where the Roth-Peikert criterion fails. We exemplify our technique on synthetic data, data from computational fluid dynamics, and on magnetohydrodynamics data. As a particularly interesting application, we demonstrate that our technique is able to extract saddle-type periodic orbits locally, and in case of high hyperbolicity at higher accuracy than traditional techniques based on integral curves.
Mobile Image Retargeting
(The Eurographics Association, 2013) Graf, Daniel; Panozzo, Daniele; Sorkine-Hornung, Olga; Michael Bronstein and Jean Favre and Kai Hormann
We propose an algorithm for axis-aligned content-aware image retargeting that is specifically optimized for mobile devices, and we show that interactive image retargeting is possible even with a low-power, mobile CPU. Our retargeting operator is based on non-uniform scaling and cropping and produces results that are on par with state-of-the-art on a large collection of images. Taking the limited screen space of mobile devices into account, we design a novel user interface that allows painting the saliency map directly onto the retargeted image while the system is continuously recomputing the retargeted result at interactive rates. Finally, we apply our algorithm in a picture gallery application to greatly improve the screen space utilization in mobile device settings.

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