Volume 27 (2008)
Permanent URI for this community
Browse
Browsing Volume 27 (2008) by Issue Date
Now showing 1 - 20 of 240
Results Per Page
Sort Options
Item The Shadow Meets the Mask: Pyramid-Based Shadow Removal(The Eurographics Association and Blackwell Publishing Ltd, 2008) Shor, Yael; Lischinski, DaniIn this paper we propose a novel method for detecting and removing shadows from a single image thereby obtaining a high-quality shadow-free image. With minimal user assistance, we first identify shadowed and lit areas on the same surface in the scene using an illumination-invariant distance measure. These areas are used to estimate the parameters of an affine shadow formation model. A novel pyramid-based restoration process is then applied to produce a shadow-free image, while avoiding loss of texture contrast and introduction of noise. Unlike previous approaches, we account for varying shadow intensity inside the shadowed region by processing it from the interior towards the boundaries. Finally, to ensure a seamless transition between the original and the recovered regions we apply image inpainting along a thin border. We demonstrate that our approach produces results that are in most cases superior in quality to those of previous shadow removal methods. We also show that it is possible to easily composite the extracted shadow onto a new background or modify its size and direction in the original image.Item Visual Inspection of Multivariate Graphs(The Eurographics Association and Blackwell Publishing Ltd., 2008) Pretorius, A. Johannes; Wijk, Jarke J. van; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerMost graph visualization techniques focus on the structure of graphs and do not offer support for dealing with node attributes and edge labels. To enable users to detect relations and patterns in terms of data associated with nodes and edges, we present a technique where this data plays a more central role. Nodes and edges are clustered based on associated data. Via direct manipulation users can interactively inspect and query the graph. Questions that can be answered include, "which edge types are activated by specific node attributes?" and, "how and from where can I reach specific types of nodes?" To validate our approach we contrast it with current practice. We also provide several examples where our method was used to study transition graphs that model real-world systems.Item Visual Abstractions of Solvent Pathlines near Protein Cavities(The Eurographics Association and Blackwell Publishing Ltd., 2008) Bidmon, Katrin; Grottel, Sebastian; Bös, Fabian; Pleiss, Jürgen; Ertl, Thomas; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerWater is known to play a crucial role in protein structure, flexibility and activity. The use of molecular dynamics simulations allows detailed studies of complex protein-solvent interactions. Cluster analysis and density-based approaches have been successfully used for the identification and analysis of conserved water molecules and hydration patterns of proteins. However, appropriate tools for analysing long-time molecular dynamics simulations with respect to tracking and visualising the paths of solvent molecules are lacking. Our method focuses on visualising the solvent paths entering and leaving cavities of the protein and allows to study the route and dynamics of the exchange of tightly bound internal water molecules with the bulk solvent. The proposed visualisation also represents dynamic properties such as direction and velocity in the solvent. Especially, by clustering similar pathlines with respect to designated properties the visualisation can be abstracted to represent the principal paths of solvent molecules through the cavities. Its application in the analysis of long-time scale molecular dynamics simulations not only confirmed conjectures based on previous manual observations made by chance, but also led to novel insights into the dynamical and structural role of water molecules and its interplay with protein structure.Item Preface, Table of Contents, Cover(The Eurographics Association and Blackwell Publishing, Inc, 2008)Item Evaluation of Illustration-inspired Techniques for Time-varying Data Visualization(The Eurographics Association and Blackwell Publishing Ltd., 2008) Joshi, Alark; Rheingans, Penny; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerIllustration-inspired techniques have provided alternative ways to visualize time-varying data. Techniques such as speedlines, flow ribbons, strobe silhouettes and opacity-based techniques provide temporal context to the current timestep being visualized. We evaluated the effectiveness of these illustrative techniques by conducting a user study. We compared the ability of subjects to visually track features using snapshots, snapshots augmented by illustration techniques, animations, and animations augmented by illustration techniques. User accuracy, time required to perform a task, and user confidence were used as measures to evaluate the techniques. The results indicate that the use of illustration-inspired techniques provides a significant improvement in user accuracy and the time required to complete the task. Subjects performed significantly better on each metric when using augmented animations as compared to augmented snapshots.Item Physically-based Dye Advection for Flow Visualization(The Eurographics Association and Blackwell Publishing Ltd., 2008) Li, Guo-Shi; Tricoche, Xavier; Hansen, Charles; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerDye advection is widely used in experimental flow analysis but has seen less use for visualization in computational fluid dynamics. One possible reason for this disconnect is the inaccuracy of the texture-based approach, which is prone to artifacts caused by numeric diffusion and mass fluctuation. In this paper, we introduce a novel 2D dye advection scheme for flow visualization based on the concept of control volume analysis typically used in computational fluid dynamics. The evolution of dye patterns in the flow field is achieved by advecting individual control volumes, which collectively cover the entire spatial domain. The local variation of dye material, represented as a piecewise quasi-parabolic function, is integrated within each control volume resulting in mass conserving transport without excessive numerical diffusion. Due to its physically based formulation, this approach is capable of conveying intricate flow structures not shown in the traditional dye advection schemes while avoiding visual artifacts.Item Generating Color Palettes using Intuitive Parameters(The Eurographics Association and Blackwell Publishing Ltd., 2008) Wijffelaars, Martijn; Vliegen, Roel; Wijk, Jarke J. van; Linden, Erik-Jan van der; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerColor is widely used in data visualization to show data values. The proper selection of colors is critical to convey information correctly. In this paper, we present a technique for generating univariate lightness ordered palettes. These are specified via intuitive input parameters that are used define the appearance of the palette: number of colors, hue, lightness, saturation, contrast and hue range. The settings of the parameters are used to generate curves through CIELUV color space. This color space is used in order to correctly translate the requirements in terms of perceptual properties to a set of colors. The presented palette generation method enables users to specify palettes that have these perceptual properties, such as perceived order, equal perceived distance and equal importance. The technique has been integrated in MagnaView, a system for multivariate data visualization.Item A Local/Global Approach to Mesh Parameterization(The Eurographics Association and Blackwell Publishing Ltd, 2008) Liu, Ligang; Zhang, Lei; Xu, Yin; Gotsman, Craig; Gortler, Steven J.We present a novel approach to parameterize a mesh with disk topology to the plane in a shape-preserving manner. Our key contribution is a local/global algorithm, which combines a local mapping of each 3D triangle to the plane, using transformations taken from a restricted set, with a global stitch operation of all triangles, involving a sparse linear system. The local transformations can be taken from a variety of families, e.g. similarities or rotations, generating different types of parameterizations. In the first case, the parameterization tries to force each 2D triangle to be an as-similar-as-possible version of its 3D counterpart. This is shown to yield results identical to those of the LSCM algorithm. In the second case, the parameterization tries to force each 2D triangle to be an as-rigid-as-possible version of its 3D counterpart. This approach preserves shape as much as possible. It is simple, effective, and fast, due to pre-factoring of the linear system involved in the global phase. Experimental results show that our approach provides almost isometric parameterizations and obtains more shape-preserving results than other state-of-the-art approaches.We present also a more general hybrid parameterization model which provides a continuous spectrum of possibilities, controlled by a single parameter. The two cases described above lie at the two ends of the spectrum. We generalize our local/global algorithm to compute these parameterizations. The local phase may also be accelerated by parallelizing the independent computations per triangle.Item Interactive Volume Rendering with Dynamic Ambient Occlusion and Color Bleeding(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ropinski, Timo; Meyer-Spradow, Jennis; Diepenbrock, Stefan; Mensmann, Joerg; Hinrichs, KlausWe propose a method for rendering volumetric data sets at interactive frame rates while supporting dynamic ambient occlusion as well as an approximation to color bleeding. In contrast to ambient occlusion approaches for polygonal data, techniques for volumetric data sets have to face additional challenges, since by changing rendering parameters, such as the transfer function or the thresholding, the structure of the data set and thus the light interactions may vary drastically. Therefore, during a preprocessing step which is independent of the rendering parameters we capture light interactions for all combinations of structures extractable from a volumetric data set. In order to compute the light interactions between the different structures, we combine this preprocessed information during rendering based on the rendering parameters defined interactively by the user. Thus our method supports interactive exploration of a volumetric data set but still gives the user control over the most important rendering parameters. For instance, if the user alters the transfer function to extract different structures from a volumetric data set the light interactions between the extracted structures are captured in the rendering while still allowing interactive frame rates. Compared to known local illumination models for volume rendering our method does not introduce any substantial rendering overhead and can be integrated easily into existing volume rendering applications. In this paper we will explain our approach, discuss the implications for interactive volume rendering and present the achieved results.Item GPU Accelerated Direct Volume Rendering on an Interactive Light Field Display(The Eurographics Association and Blackwell Publishing Ltd, 2008) Agus, Marco; Gobbetti, Enrico; Guitian, Jose Antonio Iglesias; Marton, Fabio; Pintore, GiovanniWe present a GPU accelerated volume ray casting system interactively driving a multi-user light field display. The display, driven by a single programmable GPU, is based on a specially arranged array of projectors and a holographic screen and provides full horizontal parallax. The characteristics of the display are exploited to develop a specialized volume rendering technique able to provide multiple freely moving naked-eye viewers the illusion of seeing and manipulating virtual volumetric objects floating in the display workspace. In our approach, a GPU ray-caster follows rays generated by a multiple-center-of-projection technique while sampling pre-filtered versions of the dataset at resolutions that match the varying spatial accuracy of the display. The method achieves interactive performance and provides rapid visual understanding of complex volumetric data sets even when using depth oblivious compositing techniques.Item Reduced Depth and Visual Hulls of Complex 3D Scenes(The Eurographics Association and Blackwell Publishing Ltd, 2008) Bogomjakov, Alexander; Gotsman, CraigDepth and visual hulls are useful for quick reconstruction and rendering of a 3D object based on a number of reference views. However, for many scenes, especially multi-object, these hulls may contain significant artifacts known as phantom geometry. In depth hulls the phantom geometry appears behind the scene objects in regions occluded from all the reference views. In visual hulls the phantom geometry may also appear in front of the objects because there is not enough information to unambiguously imply the object positions.In this work we identify which parts of the depth and visual hull might constitute phantom geometry. We define the notion of reduced depth hull and reduced visual hull as the parts of the corresponding hull that are phantom-free. We analyze the role of the depth information in identification of the phantom geometry. Based on this, we provide an algorithm for rendering the reduced depth hull at interactive frame-rates and suggest an approach for rendering the reduced visual hull. The rendering algorithms take advantage of modern GPU programming techniques.Our techniques bypass explicit reconstruction of the hulls, rendering the reduced depth or visual hull directly from the reference views.Item Higher Order Barycentric Coordinates(The Eurographics Association and Blackwell Publishing Ltd, 2008) Langer, Torsten; Seidel, Hans-PeterIn recent years, a wide range of generalized barycentric coordinates has been suggested. However, all of them lack control over derivatives. We show how the notion of barycentric coordinates can be extended to specify derivatives at control points. This is also known as Hermite interpolation. We introduce a method to modify existing barycentric coordinates to higher order barycentric coordinates and demonstrate, using higher order mean value coordinates, that our method, although conceptually simple and easy to implement, can be used to give easy and intuitive control at interactive frame rates over local space deformations such as rotations.Item Fitting Sharp Features with Loop Subdivision Surfaces(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ling, Ruotian; Wang, Wenping; Yan, DongmingVarious methods have been proposed for fitting subdivision surfaces to different forms of shape data (e.g., dense meshes or point clouds), but none of these methods effectively deals with shapes with sharp features, that is, creases, darts and corners. We present an effective method for fitting a Loop subdivision surface to a dense triangle mesh with sharp features. Our contribution is a new exact evaluation scheme for the Loop subdivision with all types of sharp features, which enables us to compute a fitting Loop subdivision surface for shapes with sharp features in an optimization framework. With an initial control mesh obtained from simplifying the input dense mesh using QEM, our fitting algorithm employs an iterative method to solve a nonlinear least squares problem based on the squared distances from the input mesh vertices to the fitting subdivision surface. This optimization framework depends critically on the ability to express these distances as quadratic functions of control mesh vertices using our exact evaluation scheme near sharp features. Experimental results are presented to demonstrate the effectiveness of the method.Item Automatic Registration for Articulated Shapes(The Eurographics Association and Blackwell Publishing Ltd, 2008) Chang, Will; Zwicker, MatthiasWe present an unsupervised algorithm for aligning a pair of shapes in the presence of significant articulated motion and missing data, while assuming no knowledge of a template, user-placed markers, segmentation, or the skeletal structure of the shape. We explicitly sample the motion, which gives a priori the set of possible rigid transformations between parts of the shapes. This transforms the problem into a discrete labeling problem, where the goal is to find an optimal assignment of transformations for aligning the shapes. We then apply graph cuts to optimize a novel cost function, which encodes a preference for a consistent motion assignment from both source to target and target to source. We demonstrate the robustness of our method by aligning several synthetic and real-world datasets.Item Results of a User Study on 2D Hurricane Visualization(The Eurographics Association and Blackwell Publishing Ltd., 2008) Martin, Joel P.; II, J. Edward Swan; II, Robert J. Moorhead; Liu, Zhanping; Cai, Shangshu; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerWe present the results from a user study looking at the ability of observers to mentally integrate wind direction and magnitude over a vector field. The data set chosen for the study is an MM5 (PSU/NCAR Mesoscale Model) simulation of Hurricane Lili over the Gulf of Mexico as it approaches the southeastern United States. Nine observers participated in the study. This study investigates the effect of layering on the observer's ability to determine the magnitude and direction of a vector field. We found a tendency for observers to underestimate the magnitude of the vectors and a counter-clockwise bias when determining the average direction of a vector field. We completed an additional study with two observers to try to uncover the source of the counter-clockwise bias. These results have direct implications to atmospheric scientists, but may also be able to be applied to other fields that use 2D vector fields.Item Real-time Shading with Filtered Importance Sampling(The Eurographics Association and Blackwell Publishing Ltd, 2008) Kivanek, Jaroslav; Colbert, MarkWe propose an analysis of numerical integration based on sampling theory, whereby the integration error caused by aliasing is suppressed by pre-filtering. We derive a pre-filter for evaluating the illumination integral yielding filtered importance sampling, a simple GPU-based rendering algorithm for image-based lighting. Furthermore, we extend the algorithm with real-time visibility computation. Free from any pre-computation, the algorithm supports fully dynamic scenes and, above all, is simple to implement.Item Expressive Speech Animation Synthesis with Phoneme-Level Controls(The Eurographics Association and Blackwell Publishing Ltd, 2008) Deng, Z.; Neumann, U.This paper presents a novel data-driven expressive speech animation synthesis system with phoneme-level controls. This system is based on a pre-recorded facial motion capture database, where an actress was directed to recite a pre-designed corpus with four facial expressions (neutral, happiness, anger and sadness). Given new phoneme-aligned expressive speech and its emotion modifiers as inputs, a constrained dynamic programming algorithm is used to search for best-matched captured motion clips from the processed facial motion database by minimizing a cost function. Users optionally specify hard constraints (motion-node constraints for expressing phoneme utterances) and soft constraints (emotion modifiers) to guide this search process. We also introduce a phoneme-Isomap interface for visualizing and interacting phoneme clusters that are typically composed of thousands of facial motion capture frames. On top of this novel visualization interface, users can conveniently remove contaminated motion subsequences from a large facial motion dataset. Facial animation synthesis experiments and objective comparisons between synthesized facial motion and captured motion showed that this system is effective for producing realistic expressive speech animations.Item Computational Aesthetics 2008(The Eurographics Association and Blackwell Publishing Ltd, 2008)Item Automatic Conversion of Mesh Animations into Skeleton-based Animations(The Eurographics Association and Blackwell Publishing Ltd, 2008) De Aguiar, Edilson; Theobalt, Christian; Thrun, Sebastian; Seidel, Hans-PeterRecently, it has become increasingly popular to represent animations not by means of a classical skeleton-based model, but in the form of deforming mesh sequences. The reason for this new trend is that novel mesh deformation methods as well as new surface based scene capture techniques offer a great level of flexibility during animation creation. Unfortunately, the resulting scene representation is less compact than skeletal ones and there is not yet a rich toolbox available which enables easy post-processing and modification of mesh animations. To bridge this gap between the mesh-based and the skeletal paradigm, we propose a new method that automatically extracts a plausible kinematic skeleton, skeletal motion parameters, as well as surface skinning weights from arbitrary mesh animations. By this means, deforming mesh sequences can be fully-automatically transformed into fullyrigged virtual subjects. The original input can then be quickly rendered based on the new compact bone and skin representation, and it can be easily modified using the full repertoire of already existing animation tools.Item Interactive Glossy Reflections using GPU-based Ray Tracing with Adaptive LOD(The Eurographics Association and Blackwell Publishing Ltd, 2008) Yu, Xuan; Wang, Rui; Yu, JingyiWe present an interactive GPU-based algorithm for accurately rendering high-quality, dynamic glossy reflection effects from both HDR environment maps and local scene objects. Our method uses hardware rasterization to produce primary pixels, and GPU-based BRDF importance sampling [CK07] to quickly generate reflected rays. We utilize a fast GPU ray tracer proposed by Carr et al. [CHCH06] to compute reflection hits. Our main contribution is an adaptive level-of-detail (LOD) control algorithm that greatly improves ray tracing performance during reflection shading. Specifically, we use the solid angle represented by each reflected ray to adaptively pick the level of termination in the BVH traversal step during ray tracing. This leads to 2 - 3x speedup over an unmodified implementation of [CHCH06]. Based on the same solid angle measure, we derive a texture filtering formula to reduce reflection aliasing artifacts, taking advantage of hardware MIP mapping. This extends the filtering algorithm presented in [CK07] from environment mapping to local scene reflection. Using our algorithm, we demonstrate interactive rendering rates for several scenes featuring dynamic lighting and material changes, spatially varying BRDF parameters, and rigid-body object movement.