VMV13

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

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Parallelized Global Brain Tractography
(The Eurographics Association, 2013) Philips, Stefan; Hlawitschka, Mario; Scheuermann, Gerik; Michael Bronstein and Jean Favre and Kai Hormann
Most brain tractography algorithms suffer from lower accuracy, because they use only information in a certain neighborhood and reconstruct the tracts independently. Global brain tractography algorithms compensate the lack of accuracy of those local algorithms in certain areas by optimizing the whole tractogram. The global tractography approach by Reisert et al. showed the best results in the Fiber Cup contest, but the runtime is still a matter for a medical application. In this paper we present the non-trivial parallelization of this global tractography algorithm. The parallelization exploits properties of the algorithm and modifies the algorithm where necessary. We compare the runtimes of the serial and the parallel variant and show that the outcomes of the parallel variant are of the same quality as those of the serial algorithm. The experiments proof also that the parallelization scales well for real world datasets.
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.
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.
A Tracking Approach for the Skeletonization of Tubular Parts of 3D Shapes
(The Eurographics Association, 2013) Garro, Valeria; Giachetti, Andrea; Michael Bronstein and Jean Favre and Kai Hormann
In this paper we propose a new simple and efficient method to characterize shapes by segmenting their elongated parts and characterizing them with their centerlines. We call it Tubular Section Tracking, because it consists of slicing the interested volume along different directions, tracking centroids of the extracted sections with approximately constant centroid position, area and eccentricity and refining the extracted lines with a post processing step removing bad branches and centering, joining and extending the relevant ones. We show that, even using just a few slicing directions (in some cases even just three perpendicular directions), the method is able to obtain good results, approximately pose independent and that the extracted lines can be more informative on the relevant feature of the objects than the classical skeletal lines extracted as subsets of the medial axis. Estimated lines can be used to segment shapes into meaningful parts and compute useful parameters (e.g. length, diameters).
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.
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.
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.
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/.
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.
Non-Sampled Anti-Aliasing
(The Eurographics Association, 2013) Auzinger, Thomas; Musialski, Przemyslaw; Preiner, Reinhold; Wimmer, Michael; Michael Bronstein and Jean Favre and Kai Hormann
In this paper we present a parallel method for high-quality edge anti-aliasing in rasterization. In contrast to traditional graphics hardware methods, which rely on massive oversampling to combat aliasing issues, we evaluate a closed-form solution of the associated prefilter convolution. This enables the use of a wide range of filter functions with arbitrary kernel sizes, as well as general shading methods such as texture mapping or complex illumination models. Due to the use of analytic solutions, our results are exact in the mathematical sense and provide objective ground-truth for other anti-aliasing methods and enable the rigorous comparison of different models and filters. An efficient implementation on general purpose graphics hardware is discussed and several comparisons to existing techniques and of various filter functions are given.
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.
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.
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.
Optimising Aperture Shapes for Depth Estimation
(The Eurographics Association, 2013) Sellent, Anita; Favaro, Paolo; Michael Bronstein and Jean Favre and Kai Hormann
The finite depth of field of a real camera can be used to estimate the depth structure of a scene. While the distance of an object from the plane in focus determines the defocus blur size, the shape of the aperture determines the shape of the blur. This blur shape can be manipulated by introducing masks into the main lens aperture. We propose an intuitive criterion to design aperture patterns for depth estimation. Our design criterion imposes constraints directly in the data domain and optimises the amount of depth information carried by blurred images. As a quadratic function on the aperture transmission values, our criterion can be numerically evaluated to estimate optimised aperture patterns quickly. The proposed mask optimisation procedure is applicable for different depth estimation scenarios. We consider depth estimation from two images with different focus settings and depth estimation from two images with different aperture shapes.
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.
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.
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.
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.
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.
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.

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