31-Issue 7

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

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Accurate Translucent Material Rendering under Spherical Gaussian Lights
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Yan, Ling-Qi; Zhou, Yahan; Xu, Kun; Wang, Rui; C. Bregler, P. Sander, and M. Wimmer
In this paper we present a new algorithm for accurate rendering of translucent materials under Spherical Gaussian (SG) lights. Our algorithm builds upon the quantized-diffusion BSSRDF model recently introduced in [dI11]. Our main contribution is an efficient algorithm for computing the integral of the BSSRDF with an SG light. We incorporate both single and multiple scattering components. Our model improves upon previous work by accounting for the incident angle of each individual SG light. This leads to more accurate rendering results, notably elliptical profiles from oblique illumination. In contrast, most existing models only consider the total irradiance received from all lights, hence can only generate circular profiles. Experimental results show that our method is suitable for rendering of translucent materials under finite-area lights or environment lights that can be approximated by a small number of SGs.
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.
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.
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.
Digital Camouflage Images Using Two-scale Decomposition
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Du, Hui; Jin, Xiaogang; Mao, Xiaoyang; C. Bregler, P. Sander, and M. Wimmer
We present an alternative approach to create digital camouflage images which follows human's perception intuition and complies with the physical creation procedure of artists. Our method is based on a two-scale decomposition scheme of the input images. We modify the large-scale layer of the background image by considering structural importance based on energy optimization and the detail layer by controlling its spatial variation. A gradient correction is presented to prevent halo artifacts. Users can control the difficulty level of perceiving the camouflage effect through a few parameters. Our camouflage images are natural and have less long coherent edges in the hidden region. Experimental results show that our algorithm yields visually pleasing camouflage images.
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.
A Global Parity Measure for Incomplete Point Cloud Data
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Seversky, Lee M.; Yin, Lijun; C. Bregler, P. Sander, and M. Wimmer
Shapes with complex geometric and topological features such as tunnels, neighboring sheets, and cavities are susceptible to undersampling and continue to challenge existing reconstruction techniques. In this work we introduce a new measure for point clouds to determine the likely interior and exterior regions of an object. Specifically, we adapt the concept of parity to point clouds with missing data and introduce the parity map, a global measure of parity over the volume. We first examine how parity changes over the volume with respect to missing data and develop a method for extracting topologically correct interior and exterior crusts for estimating a signed distance field and performing surface reconstruction. We evaluate our approach on real scan data representing complex shapes with missing data. Our parity measure is not only able to identify highly confident interior and exterior regions but also localizes regions of missing data. Our reconstruction results are compared to existing methods and we show that our method faithfully captures the topology and geometry of complex shapes in the presence of missing data.
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.
Hierarchical Narrative Collage For Digital Photo Album
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Zhang, Lei; Huang, Hua; C. Bregler, P. Sander, and M. Wimmer
Collage can provide a summary form on the collection of photos in an album. In this paper, we introduce a novel approach to constructing photo collage in the hierarchical narrative manner. As opposed to previous methods focusing on spatial coherence in the collage layout, our narrative collage arranges the photos according to the basic narrative elements from literary writings, i.e., character, setting and plot. Face, time and place attributes are exploited to embody those narrative elements in the collage. Then, photos are organized into the hierarchical structure for the multi-level details in the events recorded by the album. Such hierarchical narrative collage can present a visual overview in the chronological order on what happened in the album. Experimental results show that our approach offers a better summarization to browse on the photo album content than previous ones.
Homunculus Warping: Conveying Importance Using Self-intersection-free Non-homogeneous Mesh Deformation
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Reinert, Bernhard; Ritschel, Tobias; Seidel, Hans-Peter; C. Bregler, P. Sander, and M. Wimmer
Size matters. Human perception most naturally relates relative extent, area or volume to importance, nearness and weight. Reversely, conveying importance of something by depicting it at a different size is a classic artistic principle, in particular when importance varies across a domain. One striking example is the neuronal homunculus; a human figure where the size of each body part is proportional to the neural density on that part. In this work we propose an approach which changes local size of a 2D image or 3D surface and, at the same time, minimizes distortion, prevails smoothness, and, most importantly, avoids fold-overs (collisions). We employ a parallel, two-stage optimization process, that scales the shape non-uniformly according to an interactively-defined importance map and then solves for a nearby, self-intersection-free configuration. The results include an interactive 3D-rendered version of the classic sensorical homunculus but also a range of images and surfaces with different importance maps.
Improving Photo Composition Elegantly: Considering Image Similarity During Composition
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Guo, Yanwen; Liu, Ming; Gu, Tingting; Wang, Wenping; C. Bregler, P. Sander, and M. Wimmer
Optimization of images with bad compositions has attracted increasing attention in recent years. Previous methods however seldomly consider image similarity when improving composition aesthetics. This may lead to significant content changes or bring large distortions, resulting in an unpleasant user experience. In this paper, we present a new algorithm for improving image composition aesthetics, while retaining faithful, as much as possible, to the original image content. Our method computes an improved image using a unified model of composition aesthetics and image similarity. The term of composition aesthetics obeys the rule of thirds and aims to enhance image composition. The similarity term in contrast penalizes image difference and distortion caused by composition adjustment. We use an edge-based measure of structure similarity which nearly coincides with human visual perception to compare the optimized image with the original one. We describe an effective scheme to generate the optimized image with the objective model. Our algorithm is able to produce the recomposed images with minimal visual distortions in an elegant and user controllable manner. We show the superiority of our algorithm by comparing our results with those by previous methods.
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.
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.
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.
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.
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.
Preface and Table of Contents
(The Eurographics Association and Blackwell Publishing Ltd., 2012) C. Bregler, P. Sander, and M. Wimmer
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.
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.
Retrieval and Visualization of Human Motion Data via Stick Figures
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Choi, Myung Geol; Yang, Kyungyong; Igarashi, Takeo; Mitani, Jun; Lee, Jehee; C. Bregler, P. Sander, and M. Wimmer
We propose 2D stick figures as a unified medium for visualizing and searching for human motion data. The stick figures can express a wide range or human motion, and they are easy to be drawn by people without any professional training. In our interface, the user can browse overall motion by viewing the stick figure images generated from the database and retrieve them directly by using sketched stick figures as an input query. We started with a preliminary survey to observe how people draw stick figures. Based on the rules observed from the user study, we developed an algorithm converting motion data to a sequence of stick figures. The feature-based comparison method between the stick figures provides an interactive and progressive search for the users. They assist the user's sketching by showing the current retrieval result at each stroke. We demonstrate the utility of the system with a user study, in which the participants retrieved example motion segments from the database with 102 motion files by using our interface.

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