31-Issue 7

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https://diglib.eg.org/handle/10.2312/176

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    Registration Based Non-uniform Motion Deblurring
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Cho, Sunghyun; Cho, Hojin; Tai, Yu-Wing; Lee, Seungyong; C. Bregler, P. Sander, and M. Wimmer
    This paper proposes an algorithm which uses image registration to estimate a non-uniform motion blur point spread function (PSF) caused by camera shake. Our study is based on a motion blur model which models blur effects of camera shakes using a set of planar perspective projections (i.e., homographies). This representation can fully describe motions of camera shakes in 3D which cause non-uniform motion blurs. We transform the non-uniform PSF estimation problem into a set of image registration problems which estimate homographies of the motion blur model one-by-one through the Lucas-Kanade algorithm. We demonstrate the performance of our algorithm using both synthetic and real world examples. We also discuss the effectiveness and limitations of our algorithm for non-uniform deblurring.
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    Wake Synthesis For Shallow Water Equation
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Pan, Zherong; Huang, Jin; Tong, Yiying; Bao, Hujun; C. Bregler, P. Sander, and M. Wimmer
    In fluid animation, wake is one of the most important phenomena usually seen when an object is moving relative to the flow. However, in current shallow water simulation for interactive applications, this effect is greatly smeared out. In this paper, we present a method to efficiently synthesize these wakes. We adopt a generalized SPH method for shallow water simulation and two way solid fluid coupling. In addition, a 2D discrete vortex method is used to capture the detailed wake motions behind an obstacle, enriching the motion of SWE simulation. Our method is highly efficient since only 2D simulation is required. Moreover, by using a physically inspired procedural approach for particle seeding, DVM particles are only created in the wake region. Therefore, very few particles are required while still generating realistic wake patterns. When coupled with SWE, we show that these patterns can be seen using our method with marginal overhead.
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    Analytic Curve Skeletons for 3D Surface Modeling and Processing
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Thiery, Jean-Marc; Buchholz, Bert; Tierny, Julien; Boubekeur, Tamy; C. Bregler, P. Sander, and M. Wimmer
    We present a new curve skeleton model designed for surface modeling and processing. This skeleton is defined as the geometrical integration of a piecewise harmonic parameterization defined over a disk-cylinder surface decomposition. This decomposition is computed using a progressive Region Graph reduction based on both geometric and topological criteria which can be iteratively optimized to improve region boundaries. The skeleton has an analytical form with regularity inherited from the surface one. Such a form offers well-defined surface-skeleton and skeleton-surface projections. The resulting skeleton satisfies quality criteria which are relevant for skeleton-based modeling and processing. We propose applications that benefit from our skeleton model, including local thickness editing, inset surface creation for shell mapping, as well as a new mid-scale feature preserving smoothing.
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    GPU Shape Grammars
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Marvie, Jean-Eudes; Buron, Cyprien; Gautron, Pascal; Hirtzlin, Patrice; Sourimant, Gaël; C. Bregler, P. Sander, and M. Wimmer
    GPU Shape Grammars provide a solution for interactive procedural generation, tuning and visualization of massive environment elements for both video games and production rendering. Our technique generates detailed models without explicit geometry storage. To this end we reformulate the grammar expansion for generation of detailed models at the tesselation control and geometry shader stages. Using the geometry generation capabilities of modern graphics hardware, our technique generated massive, highly detailed models. GPU Shape Grammars integrate within a scalable framework by introducing automatic generation of levels of detail at reduced cost. We apply our solution for interactive generation and rendering of scenes containing thousands of buildings and trees.
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    Fur Shading and Modification based on Cone Step Mapping
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Kühnert, Tom; Brunnett, Guido; C. Bregler, P. Sander, and M. Wimmer
    This paper presents an algorithm for the real time rendering of fur without adding fur-specific geometry, such as shells, to the object. It is based on Cone Step Mapping and introduces a local distortion of the view vector to simulate a deformation of the heightfield-bound hair geometry. While this distortion enables a more realistic fur rendering, some limitations emerge and have to be dealt with. A local light reflectance model including approximations of global light interactions with hair and skin is proposed. We furthermore show how material and geometric properties can locally be influenced through standard texture mapping. This includes most notably the local modification of growth and streak direction of the hairs.
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    Texture Compression using Wavelet Decomposition
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Mavridis, Pavlos; Papaioannou, Georgios; C. Bregler, P. Sander, and M. Wimmer
    In this paper we introduce a new fixed-rate texture compression scheme based on the energy compaction properties of a modified Haar transform. The coefficients of this transform are quantized and stored using standard block compression methods, such as DXTC and BC7, ensuring simple implementation and very fast decoding speeds. Furthermore, coefficients with the highest contribution to the final image are quantized with higher accuracy, improving the overall compression quality. The proposed modifications to the standard Haar transform, along with a number of additional optimizations, improve the coefficient quantization and reduce the compression error. The resulting method offers more flexibility than the currently available texture compression formats, providing a variety of additional low bitrate encoding modes for the compression of grayscale and color textures.
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    Multi-scale Assemblage for Procedural Texturing
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Gilet, Guillaume; Dischler, Jean-Michel; Ghazanfarpour, Djamchid; C. Bregler, P. Sander, and M. Wimmer
    A procedural pattern generation process, called multi-scale ''assemblage'' is introduced. An assemblage is defined as a multi-scale composition of ''multi-variate'' statistical figures, that can be kernel functions for defining noiselike texture basis functions, or that can be patterns for defining structured procedural textures. This paper presents two main contributions: 1) a new procedural random point distribution function, that, unlike point jittering, allow us to take into account some spatial dependencies among figures and 2) a ''multi-variate'' approach that, instead of defining finite sets of constant figures, allows us to generate nearly infinite variations of figures on-the-fly. For both, we use a ''statistical shape model'', which is a representation of shape variations. Thanks to a direct GPU implementation, assemblage textures can be used to generate new classes of procedural textures for real-time rendering by preserving all characteristics of usual procedural textures, namely: infinity, definition independency (provided the figures are also definition independent) and extreme compactness.
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    Isotropic Surface Remeshing Using Constrained Centroidal Delaunay Mesh
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Chen, Zhonggui; Cao, Juan; Wang, Wenping; C. Bregler, P. Sander, and M. Wimmer
    We develop a novel isotropic remeshing method based on constrained centroidal Delaunay mesh (CCDM), a generalization of centroidal patch triangulation from 2D to mesh surface. Our method starts with resampling an input mesh with a vertex distribution according to a user-defined density function. The initial remeshing result is then progressively optimized by alternatively recovering the Delaunay mesh and moving each vertex to the centroid of its 1-ring neighborhood. The key to making such simple iterations work is an efficient optimization framework that combines both local and global optimization methods. Our method is parameterization-free, thus avoiding the metric distortion introduced by parameterization, and generating more well-shaped triangles. Our method guarantees that the topology of surface is preserved without requiring geodesic information. We conduct various experiments to demonstrate the simplicity, efficacy, and robustness of the presented method.
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    Adaptive Cross-sections of Anatomical Models
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Díaz, Jose; Monclús, Eva; Navazo, Isabel; Vázquez, Pere-Pau; C. Bregler, P. Sander, and M. Wimmer
    Medical illustrations have been used for a long time for teaching and communicating information for diagnosis or surgery planning. Illustrative visualization systems create methods and tools that adapt traditional illustration techniques to enhance the result of renderings. Clipping the volume is a popular operation in volume rendering for inspecting the inner parts, though it may remove some information of the context that is worth preserving. In this paper we present a new editing technique based on the use of clipping planes, direct structure extrusion, and illustrative methods, which preserves the context by adapting the extruded region to the structures of interest of the volumetric model. We will show that users may interactively modify the clipping plane and edit the structures to highlight, in order to easily create the desired result. Our approach works with segmented volume models and nonsegmented ones. In the last case, a local segmentation is performed on-the-fly. We will demonstrate the efficiency and utility of our method.
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    Two-Finger Gestures for 6DOF Manipulation of 3D Objects
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Liu, Jingbo; Au, Oscar Kin-Chung; Fu, Hongbo; Tai, Chiew-Lan; C. Bregler, P. Sander, and M. Wimmer
    Multitouch input devices afford effective solutions for 6DOF (six Degrees of Freedom) manipulation of 3D objects. Mainly focusing on large-size multitouch screens, existing solutions typically require at least three fingers and bimanual interaction for full 6DOF manipulation. However, single-hand, two-finger operations are preferred especially for portable multitouch devices (e.g., popular smartphones) to cause less hand occlusion and relieve the other hand for necessary tasks like holding the devices. Our key idea for full 6DOF control using only two contact fingers is to introduce two manipulation modes and two corresponding gestures by examining the moving characteristics of the two fingers, instead of the number of fingers or the directness of individual fingers as done in previous works. We solve the resulting binary classification problem using a learning-based approach. Our pilot experiment shows that with only two contact fingers and typically unimanual interaction, our technique is comparable to or even better than the state-of-the-art techniques.
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    SD Models: Super-Deformed Character Models
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Shen, Liang-Tsen; Luo, Sheng-Jie; Huang, Chun-Kai; Chen, Bing-Yu; C. Bregler, P. Sander, and M. Wimmer
    Super-deformed, SD, is a specific artistic style for Japanese manga and anime which exaggerates characters in the goal of appearing cute and funny. The SD style characters are widely used, and can be seen in many anime, CG movies, or games. However, to create an SD model often requires professional skills and considerable time and effort. In this paper, we present a novel technique to generate an SD style counterpart of a normal 3D character model. Our approach uses an optimization guided by a number of constraints that can capture the properties of the SD style. Users can also customize the results by specifying a small set of parameters related to the body proportions and the emphasis of the signature characteristics. With our technique, even a novel user can generate visually pleasing SD models in seconds.
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    Wetting Effects in Hair Simulation
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Rungjiratananon, Witawat; Kanamori, Yoshihiro; Nishita, Tomoyuki; C. Bregler, P. Sander, and M. Wimmer
    There is considerable recent progress in hair simulations, driven by the high demands in computer animated movies. However, capturing the complex interactions between hair and water is still relatively in its infancy. Such interactions are best modeled as those between water and an anisotropic permeable medium as water can flow into and out of the hair volume biased in hair fiber direction. Modeling the interaction is further challenged when the hair is allowed to move. In this paper, we introduce a simulation model that reproduces interactions between water and hair as a dynamic anisotropic permeable material. We utilize an Eulerian approach for capturing the microscopic porosity of hair and handle the wetting effects using a Cartesian bounding grid. A Lagrangian approach is used to simulate every single hair strand including interactions with each other, yielding fine-detailed dynamic hair simulation. Our model and simulation generate many interesting effects of interactions between fine-detailed dynamic hair and water, i.e., water absorption and diffusion, cohesion of wet hair strands, water flow within the hair volume, water dripping from the wet hair strands and morphological shape transformations of wet hair.
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    Realtime Two-Way Coupling of Meshless Fluids and Nonlinear FEM
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Yang, Lipeng; Li, Shuai; Hao, Aimin; Qin, Hong; C. Bregler, P. Sander, and M. Wimmer
    In this paper, we present a novel method to couple Smoothed Particle Hydrodynamics (SPH) and nonlinear FEM to animate the interaction of fluids and deformable solids in real time. To accurately model the coupling, we generate proxy particles over the boundary of deformable solids to facilitate the interaction with fluid particles, and develop an efficient method to distribute the coupling forces of proxy particles to FEM nodal points. Specifically, we employ the Total Lagrangian Explicit Dynamics (TLED) finite element algorithm for nonlinear FEM because of many of its attractive properties such as supporting massive parallelism, avoiding dynamic update of stiffness matrix computation, and efficient solver. Based on a predictor-corrector scheme for both velocity and position, different normal and tangential conditions can be realized even for shell-like thin solids. Our coupling method is entirely implemented on modern GPUs using CUDA. We demonstrate the advantage of our two-way coupling method in computer animation via various virtual scenarios.
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    Semi-supervised Mesh Segmentation and Labeling
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Lv, Jiajun; Chen, Xinlei; Huang, Jin; Bao, Hujun; C. Bregler, P. Sander, and M. Wimmer
    Recently, approaches have been put forward that focus on the recognition of mesh semantic meanings. These methods usually need prior knowledge learned from training dataset, but when the size of the training dataset is small, or the meshes are too complex, the segmentation performance will be greatly effected. This paper introduces an approach to the semantic mesh segmentation and labeling which incorporates knowledge imparted by both segmented, labeled meshes, and unsegmented, unlabeled meshes. A Conditional Random Fields (CRF) based objective function measuring the consistency of labels and faces, labels of neighbouring faces is proposed. To implant the information from the unlabeled meshes, we add an unlabeled conditional entropy into the objective function. With the entropy, the objective function is not convex and hard to optimize, so we modify the Virtual Evidence Boosting (VEB) to solve the semi-supervised problem efficiently. Our approach yields better results than those methods which only use limited labeled meshes, especially when many unlabeled meshes exist. The approach reduces the overall system cost as well as the human labelling cost required during training. We also show that combining knowledge from labeled and unlabeled meshes outperforms using either type of meshes alone.
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    Performance Capture of High-Speed Motion Using Staggered Multi-View Recording
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Wu, Di; Liu, Yebin; Ihrke, Ivo; Dai, Qionghai; Theobalt, Christian; C. Bregler, P. Sander, and M. Wimmer
    We present a markerless performance capture system that can acquire the motion and the texture of human actors performing fast movements using only commodity hardware. To this end we introduce two novel concepts: First, a staggered surround multi-view recording setup that enables us to perform model-based motion capture on motion-blurred images, and second, a model-based deblurring algorithm which is able to handle disocclusion, self-occlusion and complex object motions. We show that the model-based approach is not only a powerful strategy for tracking but also for deblurring highly complex blur patterns.
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    Approximate Bias Compensation for Rendering Scenes with Heterogeneous Participating Media
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Engelhardt, Thomas; Novák, Jan; Schmidt, Thorsten-W.; Dachsbacher, Carsten; C. Bregler, P. Sander, and M. Wimmer
    In this paper we present a novel method for high-quality rendering of scenes with participating media. Our technique is based on instant radiosity, which is used to approximate indirect illumination between surfaces by gathering light from a set of virtual point lights (VPLs). It has been shown that this principle can be applied to participating media as well, so that the combined single scattering contribution of VPLs within the medium yields full multiple scattering. As in the surface case, VPL methods for participating media are prone to singularities, which appear as bright ''splotches'' in the image. These artifacts are usually countered by clamping the VPLs' contribution, but this leads to energy loss within the short-distance light transport. Bias compensation recovers the missing energy, but previous approaches are prohibitively costly. We investigate VPL-based methods for rendering scenes with participating media, and propose a novel and efficient approximate bias compensation technique. We evaluate our technique using various test scenes, showing it to be visually indistinguishable from ground truth.
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    Improving the Parameterization of Approximate Subdivision Surfaces
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) He, Lei; Loop, Charles; Schaefer, Scott; C. Bregler, P. Sander, and M. Wimmer
    We provide a method for improving the parameterization of patching schemes that approximate Catmull-Clark subdivision surfaces, such that the new parameterization conforms better to that of the original subdivision surface. We create this reparameterization in real-time using a method that only depends on the topology of the surface and is independent of the surface's geometry. Our method can handle patches with more than one extraordinary vertex and avoids the combinatorial increase in both complexity and storage associated with multiple extraordinary vertices. Moreover, the reparameterization function is easy to implement and fast.
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    Simulation Guided Hair Dynamics Modeling from Video
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Zhang, Qing; Tong, Jing; Wang, Huamin; Pan, Zhigeng; Yang, Ruigang; C. Bregler, P. Sander, and M. Wimmer
    In this paper we present a hybrid approach to reconstruct hair dynamics from multi-view video sequences, captured under uncontrolled lighting conditions. The key of this method is a refinement approach that combines image-based reconstruction techniques with physically based hair simulation. Given an initially reconstructed sequence of hair fiber models, we develop a hair dynamics refinement system using particle-based simulation and incompressible fluid simulation. The system allows us to improve reconstructed hair fiber motions and complete missing fibers caused by occlusion or tracking failure. The refined space-time hair dynamics are consistent with video inputs and can be also used to generate novel hair animations of different hair styles. We validate this method through various real hair examples.
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    Scale Normalization for Isometric Shape Matching
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Sahillioglu, Yusuf; Yemez, Yucel; C. Bregler, P. Sander, and M. Wimmer
    We address the scale problem inherent to isometric shape correspondence in a combinatorial matching framework. We consider a particular setting of the general correspondence problem where one of the two shapes to be matched is an isometric (or nearly isometric) part of the other up to an arbitrary scale. We resolve the scale ambiguity by finding a coarse matching between shape extremities based on a novel scale-invariant isometric distortion measure. The proposed algorithm also supports (partial) dense matching, that alleviates the symmetric flip problem due to initial coarse sampling. We test the performance of our matching algorithm on several shape datasets in comparison to state of the art. Our method proves useful, not only for partial matching, but also for complete matching of semantically similar hybrid shape pairs whose maximum geodesic distances may not be compatible, a case that would fail most of the conventional isometric shape matchers.
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    Multi-Layered Automultiscopic Displays
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Ranieri, Nicola; Heinzle, Simon; Smithwick, Quinn; Reetz, Daniel; Smoot, Lanny S.; Matusik, Wojciech; Gross, Markus; C. Bregler, P. Sander, and M. Wimmer
    Our hybrid display model combines multiple automultiscopic elements volumetrically to support horizontal and vertical parallax at a larger depth of field and better accommodation cues compared to single layer elements. In this paper, we introduce a framework to analyze the bandwidth of such display devices. Based on this analysis, we show that multiple layers can achieve a wider depth of field using less bandwidth compared to single layer displays. We present a simple algorithm to distribute an input light field to multiple layers, and devise an efficient ray tracing algorithm for synthetic scenes. We demonstrate the effectiveness of our approach by both software simulation and two corresponding hardware prototypes.