VMV13

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

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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.
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.
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.
Visualizing Dissections of the Heart in a Dataflow-based Shader Framework for Volume Rendering
(The Eurographics Association, 2013) Arens, Stephan; Bolte, Matthias; Domik, Gitta; Michael Bronstein and Jean Favre and Kai Hormann
Dissections in anatomic heart illustrations are an effective visualization technique and support a variety of applications in exploration and communication. In this paper we implemented a set of volume deformations imitating dissections found in anatomy atlases of the human heart based on individual patient data. This allows physicians and surgeons to compare, explore, and discuss volume data in view of atlas illustrations. The main challenge for these illustrations is the flexible real-time combination of various (geometric) deformations and shadows (influenced by the deformations) to depict shapes and structures. The proposed technical solution to these volume visualizations is a novel GPU-based processing technique for dataflow-based shading graphs. Hence, any deformations can easily be combined in our system with immediate influence on shadows and shading. We show the effectiveness and applicability of our approach by imitating illustrations of heart dissections taken from an anatomy atlas using the patient's individual volume data.
Sampled and Analytic Rasterization
(The Eurographics Association, 2013) Auzinger, Thomas; Wimmer, Michael; Michael Bronstein and Jean Favre and Kai Hormann
In this poster we present an overview of exact anti-aliasing (AA) methods in rasterization. In contrast to the common supersampling approaches for visibility AA (e.g. MSAA) or both visibility and shading AA (e.g. SSAA, decoupled sampling), prefiltering provides the mathematically exact solution to the aliasing problem. Instead of averaging a set a supersamples, the input data is convolved with a suitable low-pass filter before sampling is applied. Recent work showed that for both visibility signals and simple shading models, a closed-form solution to the convolution integrals can be found. As our main contribution, we present a classification of both sample-based and analytic AA approaches for rasterization and analyse their strengths and weaknesses.
Transfusive Weights for Content-Aware Image Manipulation
(The Eurographics Association, 2013) Yücer, Kaan; Sorkine-Hornung, Alexander; Sorkine-Hornung, Olga; Michael Bronstein and Jean Favre and Kai Hormann
Many image editing operations, such as colorization, matting or deformation, can be performed by propagating user-defined sparse constraints (e.g. scribbles) to the rest of the image using content-aware weight functions. Image manipulation has been recently extended to simultaneous editing of multiple images of the same subject or scene by precomputing dense correspondences, where the content-aware weights play a core role in defining the sub-pixel accurate image warps from source to target images. In this paper, we expand the range of applications for content-aware weights to the multi-image setting and improve the quality of the recently proposed weights and the matching framework. We show that multiple images of a subject can be used to refine the content-aware weights, and we propose a customization of the weights to enable easily-controllable interactive depth segmentation and assignment, image matting and deformation transfer, both in single- and multi-image settings.
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.
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.
Progressive Visibility Caching for Fast Indirect Illumination
(The Eurographics Association, 2013) Ulbrich, Justus; Novák, Jan; Rehfeld, Hauke; Dachsbacher, Carsten; Michael Bronstein and Jean Favre and Kai Hormann
Rendering realistic images requires exploring the vast space of all possible paths that light can take between emitters and receivers. Thanks to the advances in rendering we can tackle this problem using different algorithms; but in general, we will likely be evaluating many expensive visibility queries. In this paper, we leverage the observation that certain kinds of visibility calculations do not need to be resolved exactly and results can be shared efficiently among similar queries. We present a visibility caching algorithm that significantly accelerates computation of diffuse and glossy inter-reflections. By estimating the visibility correlation between surface points, the cache automatically adapts to the scene geometry, placing more cache records in areas with rapidly changing visibility. We demonstrate that our approach is most suitable for progressive algorithms delivering approximate but fast previews as well as high quality converged results.
Visualization and Analysis of Lumbar Spine Canal Variability in Cohort Study Data
(The Eurographics Association, 2013) Klemm, Paul; Lawonn, Kai; Rak, Marko; Preim, Bernhard; Toennies, Klaus; Hegenscheid, Katrin; Völzke, Henry; Oeltze, Steffen; Michael Bronstein and Jean Favre and Kai Hormann
Large-scale longitudinal epidemiological studies, such as the Study of Health in Pomerania (SHIP), investigate thousands of individuals with common characteristics or experiences (a cohort) including a multitude of sociodemographic and biological factors. Unique for SHIP is the inclusion of medical image data acquired via an extensive whole-body MRI protocol. Based on this data, we study the variability of the lumbar spine and its relation to a subset of socio-demographic and biological factors. We focus on the shape of the lumbar spinal canal which plays a crucial role in understanding the causes of lower back pain. We propose an approach for the reproducible analysis of lumbar spine canal variability in a cohort. It is based on the centerline of each individual canal, which is derived from a semi-automatic, model-based detection of the lumbar spine. The centerlines are clustered by means of Agglomerative Hierarchical Clustering to form groups with low intra-group and high inter-group shape variability. The number of clusters is computed automatically. The clusters are visualized by means of representatives to reduce visual clutter and simplify a comparison between subgroups of the cohort. Special care is taken to convey the shape of the spinal canal also orthogonal to the view plane.We demonstrate our approach for 490 individuals drawn from the SHIP data.We present preliminary results of investigating the clusters with respect to their associated socio-demographic and biological factors.
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.
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.
Simulation of Time-of-Flight Sensors using Global Illumination
(The Eurographics Association, 2013) Meister, Stephan; Nair, Rahul; Kondermann, Daniel; Michael Bronstein and Jean Favre and Kai Hormann
Time-of-Flight (ToF) cameras use specialized sensors and modulated infrared light to simultaneously obtain depth, amplitude and intensity images. Depth images from such cameras suffer from various errors which exhibit a more complex behavior than traditional intensity images. Of these errors, the phenomenon of multi-reflection or multipath interference poses the biggest challenge to researchers. It is caused by indirect light paths between camera and light source and is therefore dependent on scene geometry. While simulated data can be used for ground truth evaluation and whitebox testing, current simulators do not model multipath effects. The method we present is capable of simulating all scene-dependant effects by taking global illumination into consideration. This is accomplished by modifying a bidirectional path tracing algorithm such that it takes the time-dependent propagation of modulated light in a scene into consideration. Furthermore, by combination of the proposed method with a previous hardware simulator we are capable of reproducing all effects in ToF cameras. The system was validated both on test targets with known real Time of Flight camera responses as well as qualitatively on a more complex room scene. The simulator as well as the source code is available at http://hci.iwr.uni-heidelberg.de/Benchmarks/.
A Semi-Automated Method for Subject-Specific Modeling of the Spinal Canal from Computed Tomography Images and Dynamic Radiographs
(The Eurographics Association, 2013) Haque, Md. Abedul; Marai, G. Elisabeta; Michael Bronstein and Jean Favre and Kai Hormann
Shrinkage of the spinal canal may be due to congenital or degenerative conditions, and it causes many spinerelated diseases. We present a semi-automated method to computationally reconstruct spinal canal models from static 3D images and dynamic 2D radiographs of the spine. First, we reconstruct the 3D motion of vertebrae from dynamic radiographs and compute hybrid representations of 3D bone models to facilitate computational modeling. We then use the bone position and orientation and the hybrid representations to computationally reconstruct the mesh structure of the spinal canal across the range of motion. The process requires selecting manually only a few landmark points (approximately 1%-2% of all computed vertices), and thus significantly reduces the amount of manual labor required for reconstructing a detailed geometrical model of the spinal canal. Validation on both a healthy and a fusion patient shows that the generated models can capture subject-specific characteristics of the canals and provide insight into the change of the motion pattern due to the surgery. The automation of the method will allow bioengineers to perform large scale experiments on healthy and injured spine joints and thus gain insight into underlying canal conditions.
A New Framework for Fitting Shape Models to Range Scans: Local Statistical Shape Priors Without Correspondences
(The Eurographics Association, 2013) Last, Carsten; Winkelbach, Simon; Wahl, Friedrich M.; Michael Bronstein and Jean Favre and Kai Hormann
Statistical shape models provide an important means in many applications in computer vision and computer graphics. However, the major problems are that the majority of these shape models require dense pointcorrespondences along all training shapes and that a large number of training shapes is needed in order to capture the full amount of intra-class shape variation. In this contribution, we focus on a statistical shape model that can be constructed from a set of training shapes without defining any point-correspondences. Additionally, we show how a local statistical shape model can make better use of the available shape information, greatly reducing the number of required training shapes. Finally, we present a new framework to fit this local statistical shape model without correspondences to range scans that represent incomplete parts of the trained shape class. The fitted model is then used to reproduce a natural-looking approximation of the complete shape.
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.
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.
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.
A Thin Shell Approach to the Registration of Implicit Surfaces
(The Eurographics Association, 2013) Iglesias, Jose A.; Berkels, Benjamin; Rumpf, Martin; Scherzer, Otmar; Michael Bronstein and Jean Favre and Kai Hormann
Frequently, one aims at the co-registration of geometries described implicitly by images as level sets. This paper proposes a novel shape sensitive approach for the matching of such implicit surfaces. Motivated by physical models of elastic shells a variational approach is proposed, which distinguishes two different types of energy contributions: a membrane energy measuring the rate of tangential distortion when deforming the reference surface into the template surface, and a bending energy reflecting the required amount of bending. The variational model is formulated via a narrow band approach. The built in tangential distortion energy leads to a suitable equidistribution of deformed length and area elements, under the optimal matching deformation, whereas the minimization of the bending energy fosters a proper matching of shape features such as crests, valleys or bumps. In the implementation, a spatial discretization via finite elements, a nonlinear conjugate gradient scheme with a Sobolev metric, and a cascadic multilevel optimization strategy are used. The features of the proposed method are discussed via applications both for synthetic and realistic examples.
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.

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