VMV: Vision, Modeling, and Visualization

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Application of Tensor Approximation to Multiscale Volume Feature Representations
(The Eurographics Association, 2010) Suter, Susanne K.; Zollikofer, Christoph P. E.; Pajarola, Renato; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Advanced 3D microstructural analysis in natural sciences and engineering depends ever more on modern data acquisition and imaging technologies such as micro-computed or synchrotron tomography and interactive visualization. The acquired volume data sets are not only of high-resolution but in particular exhibit complex spatial structures at different levels of scale (e.g. variable spatial expression of multiscale periodic growth structures in tooth enamel). Such highly structured volume data sets represent a tough challenge to be analyzed and explored by means of interactive visualization due to the amount of raw volume data to be processed and filtered for the desired features. As an approach to address this bottleneck by multiscale feature preserving data reduction, we propose higher-order tensor approximations (TAs). We demonstrate the power of TA to represent, and highlight the structural features in volume data. We visually and quantitatively show that TA yields high data reduction and that TA preserves volume features at multiple scales.
Graphical Interface Models for Procedural Mesh Growing
(The Eurographics Association, 2010) Menz, Stefan; Dammertz, Holger; Hanika, Johannes; Weber, Michael; Lensch, Hendrik P. A.; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Procedural modeling allows to create highly complex 3D scenes from a small set of construction rules, which has several advantages over storing the full data of an object. The most important ones are a very small memory footprint and the ability to generate infinite variations of one prototype object by using the same set of rules. However, the problem that procedural modeling imposes on the user is to define a reasonable set of rules to generate a specific object. To simplify this task, we present new interaction metaphors for a graphical user interface and a minimal set of geometric operations that allow the user to efficiently create such rules and the respective models. These metaphors are then implemented in a prototype system and are evaluated by user tests with regard to usability and user performance. The results show that the system enables even inexperienced users to create complex 3D objects via procedural modeling using the presented approach.
Interactive Multi-View Facade Image Editing
(The Eurographics Association, 2010) Musialski, Przemyslaw; Luksch, Christian; Schwärzler, Michael; Buchetics, Matthias; Maierhofer, Stefan; Purgathofer, Werner; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
We propose a system for generating high-quality approximated façade ortho-textures based on a set of perspective source photographs taken by a consumer hand-held camera. Our approach is to sample a combined orthographic approximation over the facade-plane from the input photos. In order to avoid kinks and seams which may occur on transitions between different source images, we introduce color adjustment and gradient domain stitching by solving a Poisson equation in real-time. In order to add maximum control on the one hand and easy interaction on the other, we provide several editing interactions allowing for user-guided post-processing.
Geometry-aware Video Registration
(The Eurographics Association, 2010) Palma, Gianpalo; Callieri, Marco; Dellepiane, Matteo; Corsini, Massimiliano; Scopigno, Roberto; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
We present a new method for the accurate registration of video sequences of a real object over its dense triangular mesh. The goal is to obtain an accurate video-to-geometry registration to allow the bidirectional data transfer between the 3D model and the video using the perspective projection defined by the camera model. Our solution uses two different approaches: feature-based registration by KLT video tracking, and statistic-based registration by maximizing the Mutual Information (MI) between the gradient of the frame and the gradient of the rendering of the 3D model with some illumination related properties, such as surface normals and ambient occlusion. While the first approach allows a fast registration of short sequences with simple camera movements, the MI is used to correct the drift problem that KLT tracker produces over long sequences, due to the incremental tracking and the camera motion. We demonstrate, using synthetic sequences, that the alignment error obtained with our method is smaller than the one introduced by KLT, and we show the results of some interesting and challenging real sequences of objects of different sizes, acquired under different conditions.
Ultrasound Painting of Liver Vascular Tree
(The Eurographics Association, 2010) Birkeland, Asmund; Viola, Ivan; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
In treatment planning and surgical interventions, physicians and surgeons need information about the spatial extent of specific features and the surrounding structures. Previous techniques for extracting features, based on magnetic resonance imaging and computed tomography scans, can be slow and cumbersome and are rarely used by doctors. In this paper we will present a novel approach to extract features from tracked 2D ultrasound, in particular hypo-echoic regions such as blood vessels. Features are extracted during live examinations, removing the need for slow and cumbersome post-scan processes and interaction is based on the natural interaction techniques used by doctors during the examination. The ultrasound probe is utilized as a 3D brush, painting features in a 3D environment. The painting occurs during a regular examination, producing little extra interaction from the doctor. We will introduce a novel approach to extract hypo-echoic regions from an ultrasound image and track the regions from frame to frame. 3D models are then generated by storing the outline of the region as a 3D point cloud. Automatically detecting branching, this technique can handle complex structures, such as liver vessel trees, and track multiple regions simultaneously. During the examination, the point cloud is triangulated in real-time, enabling the doctor to examine the results live and discard areas which are unsatisfactory. To enable modifications of the extracted 3D models, we present how the ultrasound probe can be used as a interaction tool for fast point cloud editing.
Pixel-Based Hyperparameter Selection for Feature-Based Image Registration
(The Eurographics Association, 2010) Brunet, Florent; Bartoli, Adrien; Navab, Nassir; Malgouyres, Rémy; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
This paper deals with parametric image registration from point correspondences in deformable environments. In this problem, it is essential to determine correct values for hyperparameters such as the number of control points of the warp, a smoothing parameter weighting a term in the cost function, or an M-estimator threshold. This is usually carried out either manually by a trial-and-error procedure or automatically by optimizing a criterion such as the Cross-Validation score. In this paper, we propose a new criterion that makes use of all the available image photometric information. We use the point correspondences as a training set to determine the warp parameters and the photometric information as a test set to tune the hyperparameters. Our approach is fully robust in the sense that it copes with both erroneous point correspondences and outliers in the images caused by, for instance, occlusions or specularities.
Coherent Background Video Inpainting through Kalman Smoothing along Trajectories
(The Eurographics Association, 2010) Bugeau, Aurélie; Gargallo, Paul; D'Hondt, Olivier; Hervieu, Alexandre; Papadakis, Nicolas; Caselles, Vicent; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Video inpainting consists in recovering the missing or corrupted parts of an image sequence so that the reconstructed sequence looks natural. For each frame, the reconstruction has to be spatially coherent with the rest of the image and temporally with respect to the reconstructions of adjacent frames. Most of existing methods only focus on inpainting foreground objects moving with a periodic motion and consider that the background is almost static. In this paper we address the problem of background inpainting and propose a method that handles dynamic background (illumination changes, moving camera, dynamic textures...). The algorithm starts by applying an image inpainting technique to each frame of the sequence and then temporally smoothes these reconstructions through Kalman smoothing along the estimated trajectories of the unknown points. The computation of the trajectories relies on the estimation of forward and backward dense optical flow fields. Several experiments and comparisons demonstrate the performance of the proposed approach.
Evaluation of Geometric Registration Methods for Using Spatial Augmented Reality in the Automotive Industry
(The Eurographics Association, 2010) Menk, Christoffer; Jundt, Eduard; Koch, Reinhard; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Spatial augmented reality is especially interesting for the automotive industry, because in the production process of a car a lot of virtual content and also real objects are used. Therefore, the virtual content can be directly projected onto the real object to combine the advantages of the real and virtual world. One important issue for the usage of spatial augmented reality in automotive processes and applications is that the virtual content has to be projected with a very high accuracy onto the real object, because decisions are made on the basis of the projection. Therefore, we present in this article a new method for the evaluation of geometric registration techniques which align a projector to a real object. Additionally, we use this proposed method to evaluate existing geometric registration techniques. Furthermore, we present a new application where a projector is used to support the design process of a new car.
Direct Resampling for Isotropic Surface Remeshing
(The Eurographics Association, 2010) Fuhrmann, Simon; Ackermann, Jens; Kalbe, Thomas; Goesele, Michael; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
We present a feature-sensitive remeshing algorithm for relaxation-based methods. The first stage of the algorithm creates a new mesh from scratch by resampling the reference mesh with an exact vertex budget with either uniform or non-uniform vertex distribution according to a density function. The newly introduced samples on the mesh surface are triangulated directly in 3D by constructing a mutual tessellation. The second stage of the algorithm optimizes the positions of the mesh vertices by building a weighted centroidal Voronoi tessellation to obtain a precise isotropic placement of the samples. We achieve isotropy by employing Lloyd's relaxation method, but other relaxation schemes are applicable. The proposed algorithm handles diverse meshes of arbitrary genus and guarantees that the remeshed model has the same topology as the input mesh. The density function can be defined by the user or derived automatically from the estimated curvature at the mesh vertices. A subset of the mesh edges may be tagged as sharp features to preserve the characteristic appearance of technical models. The new method can be applied to large meshes and produces results faster than previously achievable.
DC-Splines: Revisiting the Trilinear Interpolation on the Body-Centered Cubic Lattice
(The Eurographics Association, 2010) Domonkos, Balázs; Csébfalvi, Balázs; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
In this paper, we thoroughly study a trilinear interpolation scheme previously proposed for the Body-Centered Cubic (BCC) lattice. We think that, up to now, this technique has not received the attention that it deserves. By a frequency-domain analysis we show that it can isotropically suppress those aliasing spectra that contribute most to the postaliasing effect. Furthermore, we present an efficient GPU implementation, which requires only six trilinear texture fetches per sample. Overall, we demonstrate that the trilinear interpolation on the BCC lattice is competitive to the linear box-spline interpolation in terms of both efficiency and image quality. As a generalization to higher-order reconstruction, we introduce DC-splines that are constructed by convolving a Discrete filter with a Continuous filter, and easy to adapt to the Face-Centered Cubic (FCC) lattice as well.
Proxy-Guided Texture Synthesis for Rendering Natural Scenes
(The Eurographics Association, 2010) Bonneel, Nicolas; Panne, Michiel van de; Lefebvre, Sylvain; Drettakis, George; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Landscapes and other natural scenes are easy to photograph but difficult to model and render. We present a proxy-guided pipeline which allows for simple 3D proxy geometry to be rendered with the rich visual detail found in a suitably pre-annotated example image. This greatly simplifies the geometric modeling and texture mapping of such scenes. Our method renders at near-interactive rates and is designed by carefully adapting guidancebased texture synthesis to our goals. A guidance-map synthesis step is used to obtain silhouettes and borders that have the same rich detail as the source photo, using a Chamfer distance metric as a principled way of dealing with discrete texture labels. We adapt an efficient parallel approach to the challenging guided synthesis step we require, providing a fast and scalable solution. We provide a solution for local temporal coherence, by introducing a reprojection algorithm, which reuses earlier synthesis results when feasible, as measured by a distortion metric. Our method allows for the consistent integration of standard CG elements with the texture-synthesized elements. We demonstrate near-interactive camera motion and landscape editing on a number of examples.
The Minimal Bounding Volume Hierarchy
(The Eurographics Association, 2010) Bauszat, Pablo; Eisemann, Martin; Magnor, Marcus; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Bounding volume hierarchies (BVH) are a commonly used method for speeding up ray tracing. Even though the memory footprint of a BVH is relatively low compared to other acceleration data structures, they still can consume a large amount of memory for complex scenes and exceed the memory bounds of the host system. This can lead to a tremendous performance decrease on the order of several magnitudes. In this paper we present a novel scheme for construction and storage of BVHs that can reduce the memory consumption to less than 1% of a standard BVH. We show that our representation, which uses only 2 bits per node, is the smallest possible representation on a per node basis that does not produce empty space deadlocks. Our data structure, called the Minimal Bounding Volume Hierarchy (MVH) reduces the memory requirements in two important ways: using implicit indexing and preset surface reduction factors. Obviously, this scheme has a non-negligible computational overhead, but this overhead can be compensated to a large degree by shooting larger ray bundles instead of single rays, using a simpler intersection scheme and a two-level representation of the hierarchy. These measure enable interactive ray tracing performance without the necessity to rely on out-of-core techniques that would be inevitable for a standard BVH.
Relighting Spherical Light Fields with Polynomial Texture Mapping
(The Eurographics Association, 2010) Brückbauer, Lisa; Rezk-Salama, Christof; Kolb, Andreas; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
We present a novel image-based rendering (IBR) technique based on spherical light fields, which makes it possible to relight the captured object for arbitrary viewing positions. This approach incorporates view-dependent effects such as self-shadowing and inter-reflections. For this, we apply Polynomial Texture Maps (PTMs) to 3D objects. Once acquired, a light field representation of an object can be relit at low computation costs due to the efficiency of the PTM approach. The relighting process makes even small lighting changes visible and retains surface appearance even on a meso-scale level. Furthermore, we present a simple method to adopt specular reflections captured in the PTM to novel viewing directions.
An Interactive, Multi-Modal Approach to Analysing High-Resolution Image Mass Spectrometry Data
(The Eurographics Association, 2010) Smit, Ferdi A.; Liere, Robert van; Fornai, Lara; Heeren, Ron; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
The output resolution of imaging mass spectrometers is increasing rapidly due to advances in engineering and the use of tiling. Imaging-MS data is often displayed as a total-ion-count (TIC) image; however, anatomical structures are not easily identifiable from TIC images. For this purpose, additional high-resolution images that originate from different imaging modalities, such as stained histological data, are preferred. These modalities are most useful when fused; i.e., when the corresponding images are spatially aligned with respect to each other. The viewing and analysis of such data is ideally performed in real-time and at the highest possible resolution, allowing users to interactively query the combination of all fused data at the highest detail. However, proper alignment between modalities and interactively presenting large volumes of data is as of yet a challenge. We present a system for the simultaneous viewing and analysis of high-resolution data from different imaging modalities. Fusion is provided in such a way that interaction in one modality can be mapped to different modalities. For example, anatomical structures can be identified from histological data and their spatial extent mapped to a corresponding region-of-interest in the image MS data, allowing the analysis of its chemical compounds. In turn, the MS data can be analysed and filtered, for example using multi-variate analysis such as PCA, and the result mapped back to structures in other modalities. Level-of-detail, region-of-interest and asynchronous data processing algorithms ensure that the system can be operated interactively at the highest resolution.
Reconstructing Shape and Motion from Asynchronous Cameras
(The Eurographics Association, 2010) Klose, Felix; Lipski, Christian; Magnor, Marcus; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
We present an algorithm for scene flow reconstruction from multi-view data. The main contribution is its ability to cope with asynchronously captured videos. Our holistic approach simultaneously estimates depth, orientation and 3D motion, as a result we obtain a quasi-dense surface patch representation of the dynamic scene. The reconstruction starts with the generation of a sparse set of patches from the input views which are then iteratively expanded along the object surfaces. We show that the approach performs well for scenes ranging from single objects to cluttered real world scenarios.
Gerbil - A Novel Software Framework for Visualization and Analysis in the Multispectral Domain
(The Eurographics Association, 2010) Jordan, Johannes; Angelopoulou, Elli; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Multispectral imaging has been gaining popularity and has been gradually applied to many fields besides remote sensing. Multispectral data provides unique information about material classification and reflectance analysis in general. However, due to the high dimensionality of the data, both human observers as well as computers, have difficulty interpreting this wealth of information. We present a new software package that facilitates the visualization of the relationship between spectral and topological information in a novel fashion. It puts emphasis on the spectral gradient, which is shown to provide enhanced information for many reflectance analysis tasks. It also includes a rich toolbox for evaluation of image segmentation and other algorithms in the multispectral domain. We combine the parallel coordinates visualization technique with hashing for a highly interactive visual connection between spectral distribution, spectral gradient and topology. The framework is released as open-source, has a modern cross-platform design and is well integrated into existing established computer vision software (OpenCV).
Tuvok, an Architecture for Large Scale Volume Rendering
(The Eurographics Association, 2010) Fogal, Thomas; Krüger, Jens; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
In this paper we present the Tuvok architecture, a cross-platform open-source volume rendering system that delivers high quality, state of the art renderings at production level code quality. Due to its progressive rendering algorithm, Tuvok can interactively visualize arbitrarily large data sets even on low-end 32bit systems, though it can also take full advantage of high-end workstations with large amounts of memory and modern GPUs. To achieve this Tuvok uses an optimized out-of-core, bricked, level of detail data representation. From a software development perspective, Tuvok is composed of three independent components, a UI subsystem based on Qt, a rendering subsystem based on OpenGL and DirectX, and an IO subsystem. The IO subsystem not only handles the out-of-core data processing and paging but also includes support for many widely used file formats such as DICOM and ITK volumes. For rendering, Tuvok implements a wide variety of different rendering methods, ranging from 2D texture stack based approaches for low end hardware, to 3D slice based implementations and GPU based ray casters. All of these modes work with one- or multi-dimensional transfer functions, isosurface, and ClearView rendering modes. We also present ImageVis3D, a volume rendering application that uses the Tuvok subsystems. While these features may be found individually in other volume rendering packages, to our best knowledge this is the first open source system to deliver all of these capabilities at once.
Parallel View-Dependent Out-of-Core Progressive Meshes
(The Eurographics Association, 2010) Derzapf, Evgenij; Menzel, Nicolas; Guthe, Michael; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
The complexity of polygonal models is growing faster than the ability of graphics hardware to render them in real-time. If a scene contains many models and textures, it is often also not possible to store the entire geometry in the graphics memory. A common way to deal with such models is to use multiple levels of detail (LODs), which represent a model at different complexity levels. With view-dependent progressive meshes it is possible to render complex models in real time, but the whole progressive model must fit into graphics memory. To solve this problem out-of-core algorithms have to be used to load mesh data from external data devices. Hierarchical level of detail (HLOD) algorithms are a common solution for this problem, but they have numerous disadvantages. In this paper, we combine the advantages of view-dependent progressive meshes and HLODs by proposing a new algorithm for real-time view-dependent rendering of huge models. Using a spatial hierarchy we extend parallel view-dependent progressive meshes to support out-of-core rendering. In addition we present a compact data structure for progressive meshes, optimized for parallel GPU-processing and out-of-core memory management.
Hardware Accelerated 3D Mesh Painting
(The Eurographics Association, 2010) Schärfig, Randolf; Hormann, Kai; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
In this paper we present a new algorithm for interactively painting onto 3D meshes that exploits recent advances of GPU technology. As the user moves a brush over the 3D mesh, its paint pattern is projected onto the 3D geometry at the current viewing angle and copied to the corresponding region in the object's texture atlas. Both operations are realized on the GPU, with the advantage that all data resides in the fast GPU memory, which in turn leads to high frame rates. A main feature of our approach is the handling of seams. Whenever the brush overlaps two or more patches, this situation is detected and the paint pattern is copied correctly to the corresponding texture charts. In this way the operation of the projection into the texture atlas is completely reduced to a single texture lookup. The performance is independent of the resolution of both the brush and the texture atlas as well as the number of mesh triangles.
Visualization of Effective Connectivity of the Brain
(The Eurographics Association, 2010) Eichelbaum, Sebastian; Wiebel, Alexander; Hlawitschka, Mario; Anwander, Alfred; Knösche, Thomas; Scheuermann, Gerik; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Diffusion tensor images and higher-order diffusion images are the foundation for neuroscience researchers who are trying to gain insight into the connectome, the wiring scheme of the brain. Although modern imaging devices allow even more detailed anatomical measurements, these pure anatomical connections are not sufficient for understanding how the brain processes external stimuli. Anatomical connections constraint the causal influences between several areas of the brain, as they mediate causal influence between them. Therefore, neuroscientists developed models to represent the causal coherence between several pre-defined areas of the brain, which has been measured using fMRI, MEG, or EEG. The dynamic causal modeling (DCM) technique is one of these models and has been improved to use anatomical connection as informed priors to build the effective connectivity model. In this paper, we present a visualization method allowing neuroscientists to perceive both, the effective connectivity and the underlying anatomical connectivity in an intuitive way at the same time. The metaphor of moving information packages is used to show the relative intensity of information transfer inside the brain using a GPU based animation technique. We provide an interactive way to selectively view one or multiple effective connections while conceiving their anatomical connectivity. Additional anatomical context is supplied to give further orientation cues.

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