VMV: Vision, Modeling, and Visualization

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Multi-image Interpolation based on Graph-Cuts and Symmetric Optic Flow
(The Eurographics Association, 2010) Linz, Christian; Lipski, Christian; Magnor, Marcus A.; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Multi-image interpolation in space and time has recently received considerable attention. Typically, the interpolated image is synthesized by adaptively blending several forward-warped images. Blending itself is a low-pass filtering operation: the interpolated images are prone to blurring, even if correspondences are perfect. Furthermore, ghosting artifacts appear as soon as the underlying correspondence fields are imperfect. We address both issues and propose a multi-image interpolation algorithm that avoids blending. Instead, we cast multi-image interpolation as a labeling problem and decide for each pixel in the synthesized view from which input image to sample. Combined with a symmetrical long-range optical flow formulation for correspondence field estimation, our approach yields crisp interpolated images without ghosting artifacts.
Cost-effective Feature Enhancement for Volume Datasets
(The Eurographics Association, 2010) Díaz, Jose; Marco, Jordi; Vázquez, Pere-Pau; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Volume models often show high complexity. Local details and overall shape may sometimes be difficult to perceive. Unsharp masking techniques improve the perception of those small features by increasing the local contrast. In this paper we present a simple and fast method for feature enhancement based on 3D mipmaps. In contrast to other approaches, in addition to increasing luminance on the feature details, we also darken the valleys of the volume thus increasing local contrast and making neighboring details more visible. Our approach is fast and simple, with small memory requirements thanks to the use of 3D mipmaps. We also propose a color selection strategy, based on harmonic colors, that further enhances the salient features without abrupt or uncomfortable color changes.
Dynamic Focus + Context for Volume Rendering
(The Eurographics Association, 2010) Sikachev, Peter; Rautek, Peter; Bruckner, Stefan; Gröller, M. Eduard; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Interactive visualization is widely used in many applications for efficient representation of complex data. Many techniques make use of the focus+context approach in a static manner. These techniques do not fully make use of the interaction semantics. In this paper we present a dynamic focus+context approach that highlights salient features during user interaction. We explore rotation, panning, and zooming interaction semantics and propose several methods of changing visual representations, based on a suggested engagement-estimation method. We use DVR-MIP interpolation and a radial opacity-change approach, exploring rotation, panning, and zooming semantics. Our approach adds short animations during user interaction that help to explore the data efficiently and aid the user in the detection of unknown features.
Feature Preserving Sketching of Volume Data
(The Eurographics Association, 2010) Kerber, Jens; Bokeloh, Martin; Wand, Michael; Krüger, Jens; Seidel, Hans-Peter; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
In this paper, we present a novel method for extracting feature lines from volume data sets. This leads to a reduction of visual complexity and provides an abstraction of the original data to important structural features. We employ a new iteratively reweighted least-squares approach that allows us to detect sharp creases and to preserve important features such as corners or intersection of feature lines accurately. Traditional least-squares methods This is important for both visual quality as well as reliable further processing in feature detection algorithms. Our algorithm is efficient and easy to implement, and nevertheless effective and robust to noise. We show results for a number of different data sets.
QEM-Filtering: A New Technique for Feature-Sensitive Terrain Mesh Simplification
(The Eurographics Association, 2010) Löffler, Falko; Schumann, Heidrun; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
Terrain simplification generates multi-resolution models, from which - traditionally - irregular or semi-regular triangulations are extracted to render a terrain at a suitable level of detail. Recent terrain simplification techniques, in contrast, rely on GPU-friendly regular grids and generate multiple resolutions by applying the filtering and sub-sampling paradigm. However, due to the smoothing and uniform sampling, these techniques sparsely approximate the terrain surface. Consequently, in order to guarantee a certain error threshold, considerably more triangles need to be rendered. In this paper, we present a novel feature-sensitive simplification technique. Our approach follows the aforementioned paradigm. The key idea is to maintain the regularity while recomputing the vertex positions by taking a specific error metric into account, namely the quadric error metric (QEM). Compared to previous approaches, we apply the paradigm to the grid of vertex-associated quadrics. From these we extract vertices of the new resolution by relying on quadric error minimization. We, thus, maintain the regular grid structure while preserving terrain features. Compared to methods, which are solely based on vertex-filtering and sub-sampling, our approach reduces the approximation error. As a consequence, we require fewer triangles, which improves the rendering performance.
3D Curve-Skeleton Extraction Algorithm Using a Pseudo-Normal Vector Field
(The Eurographics Association, 2010) Pantuwong, Natapon; Sugimoto, Masanori; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
A curve skeleton is a line representation of a 3D object. It is useful in many applications, such as animation, shape matching or scientific analysis. The method described in this paper extracts a curve skeleton from the vector field which is created inside the 3D object. The topology of the vector field is analyzed to obtain the curve skeleton. In contrast with previous methods, the vector field is calculated using a pseudo-normal vector. Furthermore, by using the proposed skeleton-growing method, the vector field topology need not be computed for every voxel. Therefore, the proposed approach requires significantly less computation compared with previous vector field-based approaches, while still capturing all important parts of 3D object. The proposed method is very useful for any applications, especially real-time applications such as quick animation production and prototyping of graphical systems.
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.
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.
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.
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.
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.
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.
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.
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.
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).
Global Illumination using Parallel Global Ray-Bundles
(The Eurographics Association, 2010) Hermes, Jan; Henrich, Niklas; Grosch, Thorsten; Mueller, Stefan; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
A fast computation of unbiased global illumination is still an unsolved problem, especially if multiple bounces of light and non-diffuse materials are included. The standard Monte Carlo methods are time-consuming, because many incoherent rays are shot into the scene, which is hard to parallelize. On the other hand, GPUs can make the most of their computing power if the problem can be broken down into many parallel, small tasks. Casting global, parallel ray-bundles into the scene is a way of achieving this parallelism. We exploit modern GPU features to extract all intersection points along each ray within a single rendering pass. Radiance can then be transferred between pairs of all points which allows an arbitrary number of interreflections, especially for compelling multiple glossy reflections. Beside arbitrary BRDFs, our method is independent of the number of light sources and can handle arbitrary shaped light sources in a unified framework for unbiased global illumination. Since many methods exist for fast computation of direct light using soft shadows, we demonstrate how our method can be built on top of any direct light simulation.
Image-Error-Based Level of Detail for Landscape Visualization
(The Eurographics Association, 2010) Clasen, Malte; Prohaska, Steffen; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
We present a quasi-continuous level of detail method that is based on an image error metric to minimize the visual error. The method is designed for objects of high geometric complexity such as trees. By successive simplifications, it constructs a level of detail hierarchy of unconnected primitives (ellipsoids, lines) to approximate the input models at increasingly coarser levels. The hierarchy is constructed automatically without manual intervention. When rendering roughly 100k model instances at a low visual error compared to rendering the full resolution model, our method is two times faster than billboard clouds.
Real-time Full-body Visual Traits Recognition from Image Sequences
(The Eurographics Association, 2010) Jung, Christoph; Tausch, Reimar; Wojek, Christian; Reinhard Koch and Andreas Kolb and Christof Rezk-Salama
The automatic recognition of human visual traits from images is a challenging computer vision task. Visual traits describe for example gender and age, or other properties of a person that can be derived from visual appearance. Gathering anonymous knowledge about people from visual cues bears potential for many interesting applications, as for example in the area of human machine interfacing, targeted advertisement or video surveillance. Most related work investigates visual traits recognition from facial features of a person, with good recognition performance. Few systems have recently applied recognition on low resolution full-body images, which shows lower performance than the facial regions but already can deliver classification results even if no face is visible. Obviously full-body classification is more challenging, mainly due to large variations in body pose, clothing and occlusion. In our study we present an approach to human visual traits recognition, based on Histogram of oriented Gradients (HoG), colour features and Support Vector Machines (SVM). In this experimental study we focus on gender classification. Motivated by our application of real-time adaptive advertisement on public situated displays, and unlike previous works, we perform a thorough evaluation on much more comprehensive datasets that include hard cases like side- and back views. The extended annotations used in our evaluation will be published. We further show that a hierarchical classification scheme to disambiguate a person's directional orientation and additional colour features can increase recognition rates. Finally, we demonstrate that temporal integration of per-frame classification scores significantly improves the overall classification performance for tracked individuals and clearly outperforms current state-of-the-art accuracy for single images.

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