VMV13

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

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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.
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.
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.
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.
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.
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 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.
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.
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.
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/.
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.
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.
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.
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.
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.
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.
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.
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.

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