VMV11

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https://diglib.eg.org/handle/10.2312/1015

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Adaptive Level-of-Precision for GPU-Rendering
(The Eurographics Association, 2011) Meyer, Quirin; Sussner, Gerd; Greiner, Günter; Stamminger, Marc; Peter Eisert and Joachim Hornegger and Konrad Polthier
Video memory is a valuable resource that has grown much slower than the rendering power of GPUs over the last years. Today, video memory is often the limiting factor in interactive high-quality rendering applications. The most often used solution to reduce memory consumption is to apply level-of-detail (LOD) methods: only a simplified version of the mesh with less vertices and triangles is kept in memory. In this paper we examine a simple orthogonal compression approach that is mostly neglected: adapting the level-of-precision (LOP) of vertex data. The main idea is to quantize vertex positions according to the current view distance, and adapt precision by adding or removing single bit planes. We provide an analysis of the resulting image error, and show that visual artifacts can be avoided by simply constraining the quantization for critical vertices. Our approach allows both random access on vertex data as well as quickly switching between LOP. In experiments we found that our approach compresses vertex positions by about 70percent on average without loss in rendering performance or image quality.
Adaptive Sampling for Geometry-aware Reconstruction Filters
(The Eurographics Association, 2011) Bauszat, Pablo; Eisemann, Martin; Magnor, Marcus; Peter Eisert and Joachim Hornegger and Konrad Polthier
We present an adaptive sampling scheme for Monte-Carlo-based renderers with the aim to support geometryaware filtering techniques for interactive computation of global illumination. While sophisticated filtering techniques for homogeneous areas can already produce high-quality results with as few as one sample per pixel, these approaches lack the ability to filter sufficiently in the vicinity of complex geometric structures. The result are visible artifacts in the final rendering result. Our sampling scheme distributes the samples for the indirect illumination in the image plane according to the necessity of a geometry-aware filtering. We show how to implement our scheme efficiently on current graphics hardware and how to combine it with a sophisticated filtering in order to achieve high-quality interactive frame rates for global illumination simulations. The resulting computational overhead is only in the range of a few milliseconds, making our approach suitable for real-time implementations.
AFiT - Atrial Fibrillation Ablation Planning Tool
(The Eurographics Association, 2011) Brost, Alexander B.; Bourier, Felix; Kleinoeder, Andreas; Raab, Jens; Koch, Martin; Stamminger, Marc; Hornegger, Joachim; Strobel, Norbert; Kurzidim, Klaus; Peter Eisert and Joachim Hornegger and Konrad Polthier
The planning of cryo-balloon ablations for treatment of atrial fibrillation is a crucial task for a physician as he has to determine which size of the balloon catheter is required for isolation at each pulmonary vein. Today, the diameter of the pulmonary vein's ostium is measured in a pre-operative data set to determine which type of catheter is most appropriate. We present a novel tool that visualizes a cryo-balloon catheter model within a 3-D model representing a segmented left atrium. Using this approach, physicians are able to better assess the catheter fit. So far, measurement of the pulmonary vein diameters have been performed by evaluation of 2-D slices taken from pre-operative data sets. The first feedback obtained by physicians was very encouraging as this tool offers better insights for balloon catheter ablation procedures.
Assessment of Time-of-Flight Cameras for Short Camera-Object Distances
(The Eurographics Association, 2011) Stürmer, Michael; Becker, Guido; Hornegger, Joachim; Peter Eisert and Joachim Hornegger and Konrad Polthier
In this paper we have compared Time-of-Flight cameras of different vendors at object-camera distances of 500 mm, 1500 mm and 2500 mm. The aim was to find the highest possible precision at the distance of 500 mm, to estimate the change of the accuracy depending on scene-reflectivity and working distance and to investigate the possibility to use the cameras as per-pixel sub-centimeter accurate measuring devices. To this end, we have evaluated the variation of the distance measurement noise over several distances as well as the minimum noise we could achieve with each camera. As the amplitude-dependent distance error may become significantly large, we also tried to quantify it in order to estimate if it can be reduced to fulfill given accuracy requirements. We compared a Camcube3 from PMD Technologies, a Swissranger4000 from MESA Imaging and a C70E from Fotonic. All cameras showed different behaviors in terms of temporal noise, variation of noise and amplitude dependency. The Camcube showed the strongest amplitude dependent effects. The minimum standard deviations at 500 mm distance were at 4.8 mm for the Camcube, 1.6 mm for the Swissranger and 0.9 mm for the C70E.
Auto-Tilt Photography
(The Eurographics Association, 2011) Sadlo, Filip; Dachsbacher, Carsten; Peter Eisert and Joachim Hornegger and Konrad Polthier
Tilt-shift camera lenses are a powerful artistic tool to achieve effects like selective focus with very shallow depth of field. Typically they are used by professional photographers only, which is due to the high cost and weight, and the intricate, non-intuitive handling. We introduce the auto-tilt mechanism which is as easy to use as the standard autofocus. It allows automatic sharp focus of objects not parallel to the image plane, such as in landscape photography where getting everything sharp is often desirable. In contrast to pure computational approaches that are based on resampling from focal stacks, our approach based on true exposures enables time-dependent scenes and higher image quality. Auto-tilt can also be controlled via a simple sketching user-interface letting the photographer quickly define image regions inside and outside sharp focus. We demonstrate auto-tilt using a simple rapidly prototyped experimental setup that tilts the sensor (as opposed to classic tilt-shift lenses), and describe possible implementations in off-the-shelf cameras. We also outline future prospects with flexible image sensors currently being developed.
AVDT - Automatic Visualization of Descriptive Texts
(The Eurographics Association, 2011) Spika, Christian; Schwarz, Katharina; Dammertz, Holger; Lensch, Hendrik P. A.; Peter Eisert and Joachim Hornegger and Konrad Polthier
Expressing mental images visually as 3D scenes is a time-consuming challenge. Therefore, we employ natural language to facilitate the creation of virtual environments. In this paper, we present a framework, which automatically converts an arbitrary descriptive text into a representative 3D scene. Our system parses a user-written input text, extracts information using techniques from Natural Language Processing (NLP) and identifies relevant units. Based on derived object-to-object relations, our system associates every object with an appropriate 3D model and evaluates spatial dependencies of the entities. The resulting locations are combined based on adequate heuristics in order to create natural looking virtual environments. Finally, a physics engine is used to render a realistic and interactive 3D scene which enables the user to actively manipulate the stage setup.
Bent Normals and Cones in Screen-space
(The Eurographics Association, 2011) Klehm, Oliver; Ritschel, Tobias; Eisemann, Elmar; Seidel, Hans-Peter; Peter Eisert and Joachim Hornegger and Konrad Polthier
Ambient occlusion (AO) is a popular technique for real-time as well as offline rendering. One of its benefits is a gain in efficiency due to the fact that occlusion and shading are decoupled which results in an average occlusion that modulates the surface shading. Its main drawback is a loss of realism due to the lack of directional occlusion and lighting. As a solution, the use of bent normals was proposed for offline rendering. This work describes how to compute bent normals and bent cones in combination with screen-space ambient occlusion. These extensions combine the speed and simplicity of AO with physically more plausible lighting.
A Cluster Hierarchy-based Volume Rendering Approach for Interactive Visual Exploration of Multi-variate Volume Data
(The Eurographics Association, 2011) Dobrev, Petar; Long, Tran Van; Linsen, Lars; Peter Eisert and Joachim Hornegger and Konrad Polthier
Interactive visual analysis of volumetric data relies on intuitive, yet powerful mechanisms to generate transfer functions. For multi-variate data, traditional methods for interactive transfer functions generation are of limited use. We propose a novel approach, where the user operates in a cluster space. It relies on hierarchical densitybased clustering of the high-dimensional feature space. The cluster tree visualization in form of a 2D radial layout serves as an interaction widget for selecting clusters, assigning material properties, changing sizes, merging, and splitting. This widget is complemented by a linked parallel coordinates widget. The interactive selections are automatically mapped to a transfer function for a linked 3D texture-based direct volume rendering, where brushing in parallel coordinates leads to the generation of a 3D binary opacity mask that is overlaid with the opacity values obtained from cluster tree selections. In GPU memory, we only hold the density values from the clustering approach and the cluster IDs. The derived density field allows us to interactively change the size of clusters and to compute normals for lighting. We applied our methods to the visualization of multi-variate data consisting of multiple scalar fields as well as derived scalar property fields from single scalar and vector fields. Our approach scales well to arbitrarily high dimensionality as the complexity of the main user interactions do not increase with the number of dimensions.
A Clustering-based Visualization Technique to Emphasize Meaningful Regions of Vector Fields
(The Eurographics Association, 2011) Kuhn, Alexander; Lehmann, Dirk J.; Gaststeiger, Rocco; Neugebauer, Matthias; Preim, Bernhard; Theisel, Holger; Peter Eisert and Joachim Hornegger and Konrad Polthier
This paper proposes a vector field visualization approach that extracts and visualizes grouped regions of static 3D vector fields of similar curvature behavior. These regions are argued to ease the recognition of regions of potential interest and accelerate the general exploration process of vector fields. Our approach detects regions of similar geometric stream properties such as integral curvature and visualizes them by means of compact cluster boundaries. To supplement existing approaches our method combines information on relevant scales to extract meaningful semantical aspects of the overall field structure. For proof of concept we illustrate our results based on real and synthetic data sets.
Data-Driven Visualization of Functional Brain Regions from Resting State fMRI Data
(The Eurographics Association, 2011) Crippa, Alessandro; Roerdink, Jos B.T.M.; Peter Eisert and Joachim Hornegger and Konrad Polthier
Functional parcellation of the human cortex plays an important role in the understanding of brain functions. Tradi- tionally, functional areas are defined according to anatomical landmarks. Recently, new techniques were proposed that do not require a priori segmentation of the cortex. Such methods allow functional parcellation by functional information alone. We propose here a data-driven approach for the exploration of functional connectivity of the cortex. The method extends a known parcellation method, used in multichannel EEG analysis, to define and extract functional units (FUs), i.e., spatially connected brain regions that record highly correlated fMRI signals. We apply the method to the study of fMRI data and provide a visualization, inspired by the EEG case, that uses linked views to facilitate the understanding of both the location and the functional similarity of brain regions. Initial feedback on our approach was received from four domain experts, researchers in the field of neuroscience.
Depth Driven Photometric and Geometric Image Registration for Real-Time Stereo Systems
(The Eurographics Association, 2011) Waizenegger, Wolfgang; Feldmann, Ingo; Eisert, Peter; Peter Eisert and Joachim Hornegger and Konrad Polthier
This paper presents a novel depth driven approach for a highly accurate joint photometric and geometric image alignment. Thereby, the registration problem is expressed in terms of a consistent, elegant and efficient energy formulation. Moreover, we propose a real-time capable alternating iterative optimization scheme to solve for a state of minimal energy. Since our energy formulation is based on pixel wise color similarity our registration procedure directly improves the performance of disparity estimation and the visual quality of multi-view view synthesis.
Direct Visualization of Particle-Partition of Unity Data
(The Eurographics Association, 2011) Üffinger, Markus; Schweitzer, Marc Alexander; Sadlo, Filip; Ertl, Thomas; Peter Eisert and Joachim Hornegger and Konrad Polthier
Direct visualization of higher-order data provides manifold advantages over the traditional approach, which is based on resampling and subsequent visualization by interpolation-based techniques. Most important, it avoids excessive computation and consumption of memory, and prevents artifacts by pixel-accurate visualization at interactive rates. This work addresses particle-partition of unity simulation data, where fields are modeled both using cell-based analytic representations together with enrichment functions centered at individual points. This combination of bases allows for superior simulation convergence rates and is able to capture high field variations with comparably small sets of basis functions. In this paper we propose direct visualization of such data from 2D simulations, providing accurate insight. We additionally visualize solver performance, allowing for more directed simulation design, and exemplify our technique using a GPU-based prototype on crack simulation examples.
Effective Back-Patch Culling for Hardware Tessellation
(The Eurographics Association, 2011) Loop, Charles; Nießner, Matthias; Eisenacher, Christian; Peter Eisert and Joachim Hornegger and Konrad Polthier
When rendering objects with hardware tessellation, back-facing patches should be culled as early as possible to avoid unnecessary surface evaluations, and setup costs for the tessellator and rasterizer. For dynamic objects the popular cone-of-normals approach is usually approximated using tangent and bitangent cones. This is faster to compute, but less effective. We present a novel approach using the Bézier convex hull of the parametric tangent plane. It is much more accurate, and by operating in clip space we are able to reduce the computational cost significantly. As our algorithm vectorizes well, we observe comparable test times with increased cull-rates.
Extracting Flow Structures Using Sparse Particles
(The Eurographics Association, 2011) Agranovsky, Alexy; Garth, Christoph; Joy, Kenneth I.; Peter Eisert and Joachim Hornegger and Konrad Polthier
In recent years, Lagrangian Coherent Structures (LCS) have been characterized using the Finite-Time Lyapunov Exponent, following the advection of a dense set of particles into a corresponding flow field. The large amount of particles needed to sufficiently map a flow field has been a non-trivial computational burden in the application of LCS. By seeding a minimal amount of particles into the flow field, Moving Least Squares, combined with FTLE, will extrapolate the important feature locations at which further refinement is desired. Following the refinement procedure, MLS produces a continuous function reconstruction allowing the characterization of Lagrangian Coherent Structures with a lower number of particles. Through multiple data sets, we show that given a sparse and refined sampling, MLS will reproduce FTLE fields exhibiting a nominal error while maintaining a performance increase when compared to the standard, dense finite difference approach.
Extrinsic Self-Calibration of Time-of-Flight Cameras using a Combination of 3D and Intensity Descriptors
(The Eurographics Association, 2011) Schmidt, Jörn; Brückner, Marcel; Denzler, Joachim; Peter Eisert and Joachim Hornegger and Konrad Polthier
Time-of-Flight (ToF) cameras are able to simultaneously record intensity and depth images at a high frequency. Many applications require images that are recorded from different viewpoints. In order to consolidate the recorded data into a common coordinate system, the extrinsic calibration between the cameras needs to be known. From a practical point of view this calibration should be accomplished without any user interaction or artificial calibration objects. Classical approaches for extrinsic self-calibration fail to extract correct point correspondences and do not exploit the important information provided by the depth images. In this paper we discuss the characteristics of extrinsic ToF camera calibration and present a descriptor combination for the extraction of 3D point correspondences. Several experiments on real data demonstrate the robustness and high accuracy of our approach. Our method outperforms the state-of-the-art approach for point correspondence extraction in classical camera images.
Fast and Efficient 3D Chamfer Distance Transform for Polygonal Meshes
(The Eurographics Association, 2011) Martinek, Michael; Grosso, Roberto; Greiner, Günther; Peter Eisert and Joachim Hornegger and Konrad Polthier
We present an efficient GPU-based method to perform 3D chamfer distance transform (CDT) in a wavefront scheme. In this context, we also introduce a binary voxelization algorithm which provides the initial boundary condition for the CDT. The voxelization method is capable of both, surface and solid voxelization, allowing for the computation of unsigned distance fields for arbitrary polygonal meshes and signed distances for models with orientable surfaces. Our method is trimmed on speed rather than accuracy. It works with simple chamfer metrics such as the Manhattan and chessboard distance and requires only a single rendering pass per distance layer. Due to the wavefront scheme, a propagation can be stopped if a required number of distance layers is reached. However, even a complete distance field can be computed in the magnitude of 10?3 seconds including the preprocessing voxelization step. This allows for a use in real-time applications such as path planning or proximity computations. We demonstrate the application of our method for the latter.
A Framework for Interactive Visualization and Classification of Dynamical Processes at the Water Surface
(The Eurographics Association, 2011) Wanner, Sven; Sommer, Christoph; Rocholz, Roland; Jung, Michael; Hamprecht, Fred; Jähne, Bernd; Peter Eisert and Joachim Hornegger and Konrad Polthier
A framework for the visualization and classification of multi-channel spatio-temporal data from water wave imaging is presented. Our interactive visualization tool, WaveVis, allows a detailed study of the water surface shape in reference to additional data streams, like thermographic images or classification results. This facilitates an intuitive and effective inspection of huge amounts of data. WaveVis was used to select representative training examples of events for a supervised learning approach and to evaluate the results of the classification. The interactive classification and segmentation software ilastik was used to train a Random Forest classifier. The benefit of the combination of both programs is demonstrated for two applications, the estimation of the rain rate from the segmentation of impact craters, and the detection of small scale breaking waves. The classification of the impact crater of raindrops on the water surface worked very well, whereas the detection of the breaking waves was satisfactory only under certain experimental conditions. Nevertheless, the combination of WaveVis and ilastik proved to be valuable in both cases.
FreeCam: A Hybrid Camera System for Interactive Free-Viewpoint Video
(The Eurographics Association, 2011) Kuster, Claudia; Popa, Tiberiu; Zach, Christopher; Gotsman, Craig; Gross, Markus; Peter Eisert and Joachim Hornegger and Konrad Polthier
We describe FreeCam - a system capable of generating live free-viewpoint video by simulating the output of a virtual camera moving through a dynamic scene. The FreeCam sensing hardware consists of a small number of static color video cameras and state-of-the-art Kinect depth sensors, and the FreeCam software uses a number of advanced GPU processing and rendering techniques to seamlessly merge the input streams, providing a pleasant user experience. A system such as FreeCam is critical for applications such as telepresence, 3D video-conferencing and interactive 3D TV. FreeCam may also be used to produce multi-view video, which is critical to drive newgeneration autostereoscopic lenticular 3D displays.
A Global Optimization Approach to High-detail Reconstruction of the Head
(The Eurographics Association, 2011) Schneider, David C.; Kettern, Markus; Hilsmann, Anna; Eisert, Peter; Peter Eisert and Joachim Hornegger and Konrad Polthier
The paper presents an approach for reconstructing head-and-shoulder portraits of people from calibrated stereo images with a high level of geometric detail. In contrast to many existing systems, our reconstructions cover the full head, including hair. This is achieved using a global intensity-based optimization approach which is stated as a parametric warp estimation problem and solved in a robust Gauss-Newton framework. We formulate a computationally efficient warp function for mesh-based estimation of depth which is based on a well known image-registration approach and adapted to the problem of 3D reconstruction. We address the use of sparse correspondence estimates for initializing the optimization as well as a coarse-to-fine scheme for reconstructing without specific initialization. We discuss issues of regularization and brightness constancy violations and show various results to demonstrate the effectiveness of the approach.
Implicit Filtering for Image and Shape Processing
(The Eurographics Association, 2011) Belyaev, Alexander; Yamauchi, Hitoshi; Peter Eisert and Joachim Hornegger and Konrad Polthier
The main purpose of this paper consists of demonstrating advantages of using implicit filtering schemes (noncausal IIR filters, in the signal processing language) for some basic image processing and geometric modeling applications. In particular, applications of implicit filtering for curve subdivision, image filtering, estimating image derivatives, and deblurring Gaussian blur are considered.

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