Short Papers

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https://diglib.eg.org/handle/10.2312/271

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A Dynamic Caching System for Rendering an Animated Crowd in Real-Time
(The Eurographics Association, 2009) Lister, Wayne; Laycock, Robert G.; Day, Andrew M.; P. Alliez and M. Magnor
We present a method to accelerate the rendering of large crowds of animated characters. Recent trends have seen matrix-palette skinning become the prevalent approach due to its low memory overhead and fully dynamic geometry. However, the performance of skeletal animation remains modest in comparison to static rendering since neither temporal nor intra-frame coherency can be exploited. We cast crowd rendering as a memory-management problem and allocate a small geometry cache on the GPU within which animated characters can be stored. This serves to augment matrix-palette skinning with baked geometry and allows animation frames to be re-used by multi-pass rendering, between multiple agents and across multiple frames. Our method builds its cache dynamically and adapts to the current simulation state through use of the page-replacement algorithms traditionally employed by virtual-memory systems. In many cases this negates the need for skinning altogether and enables thousands of characters to be rendered in real-time, each independently animated and without loss of fidelity.
A Real-time Interactive Tool for Image Cutout
(The Eurographics Association, 2009) Liu, Chen; Li, Fengxia; Zhang, Yan; Zhan, Shouyi; P. Alliez and M. Magnor
We present an interactive tool for extracting foreground objects from image in real-time. As seen from the object boundary, the segmentation is to split pixel-pairs right on the boundary. The system utilizes the user input while the user roughly paints the stroke along the object boundary. Either side of the stroke is assumed to lie in foreground or background, and the mouse trace is supposed to coarsely indicate the object contour. We use the appearance, gradient and contour information to formulate the segmentation problem to an energy minimization problem, which is solved by graph cut. The appearance model is built via local sampling, since it often provides more discriminative model in local areas than that from global sampling. In addition, our system can dynamically adjust the stroke and the optimization region for which segmentation needs to be computed. The optimization region is much smaller than the whole image. This greatly reduces the computational complexity in each iteration and also gives the system the ability of incrementally segmenting. Experiments show the effectiveness of our methods in improving the segmentation performance.
Continuous Search and Replace in Vector Graphics
(The Eurographics Association, 2009) Loviscach, Joern; P. Alliez and M. Magnor
Many types of vector graphics comprise large numbers of almost identical partial shapes such as serifs in typeface design, ornaments in illustrations, and stylistic elements in icon design. As of today, later design changes of such shapes require the user to edit every instance on its own. Standard features of vector graphics software help with the automated replacement of stand-alone graphical objects, but do not cover partial shapes. Hence, a geometric search & replace function is needed, which is exacerbated by the circumstance that the repeated shapes construction from curve segments tends to vary from instance to instance, which requires a continuous approach that does not rely on a fixed division of a path into segments. This paper presents a geometric search and replace function that addresses these issues, possesses adjustable tolerance against orientation and size changes between the search pattern shape and the retrieved shapes, and is integrated with a standard vector graphics program.
Dent Removal: Geodesic Curve-Based Mesh Fairing
(The Eurographics Association, 2009) Pinskiy, Dmitriy; P. Alliez and M. Magnor
This paper presents a novel mesh fairing method to remove unwanted geometric artifacts such as dents. The key element of the proposed method is our unique algorithm for the assignment of weights in the discrete Laplacian. Our weights reflect the orientation of the first ring of vertices around a given vertex with respect to the whole dented region, rather than the ring's local geometry (e.g. Gauss or mean curvature flow that needs to be reestimated per each iteration). To establish the dent region s global behavior, we perform principal curvature analysis to determine representative geodesic curves for the surface. Our method is efficient as it only needs to compute the geodesic curves once, and then it uses them to guide subsequent iterations of anisotropic relaxation.
Real-time Volumetric Lighting in Participating Media
(The Eurographics Association, 2009) Toth, Balazs; Umenhoffer, Tamas; P. Alliez and M. Magnor
Simulating light scattering in participating media, such as dust, fog or smoke, can greatly improve the overall realism of the images. This volumetric effect has been well studied in the context of off-line rendering but is still challenging for interactive applications. In this paper we present a GPU-based algorithm to compute volumetric light-shafts generated by single scattering in participating media. The proposed method uses shadow maps to account for shadowing and interleaved sampling to maintain high frame rates without sacrificing image quality.
Preface and Table of Contents
(The Eurographics Association, 2009) Alliez, P.; Magnor, M.; P. Alliez and M. Magnor
Preface and Table of Contents
Tile-based Image Forces for Active Contours on GPU
(The Eurographics Association, 2009) Kienel, Enrico; Brunnett, Guido; P. Alliez and M. Magnor
Active contours have been proven to be powerful semiautomatic image segmentation tools. We present an adaptive image force computation scheme in order to minimize both computational and memory requirements. Hence, we are able to perform a fast semiautomatic contour detection in huge images. We present an efficient implementation of this approach on the basis of general purpose GPU processing providing a visual continuous active contour deformation.
Video-Realistic Image-based Eye Animation System
(The Eurographics Association, 2009) Weissenfeld, Axel; Liu, Kang; Ostermann, J.; P. Alliez and M. Magnor
In this work we elaborate on a novel image-based system for creating video-realistic eye animations to arbitrary spoken output. These animations are useful to give a face to multimedia applications such as virtual operators in dialog systems. Our eye animation system consists of two parts: eye control unit and rendering engine. The designed eye control unit is based on the statistical analysis of recorded human subjects. We design a new model, which fully automatically couples eye blinks and movements with phonetic as well as prosodic information extracted from spoken language. Subjective tests showed that participants are not able to distinguish between real eye motions and our animations, which has not been achieved before.
Volume Conserving Simulation of Deformable Bodies
(The Eurographics Association, 2009) Diziol, Raphael; Bender, Jan; Bayer, Daniel; P. Alliez and M. Magnor
We present a new method for simulating volume conserving deformable bodies using an impulse-based approach. In order to simulate a deformable body a tetrahedral model is generated from an arbitrary triangle mesh. All resulting tetrahedrons are assigned to volume constraints which ensure the conservation of the total volume. For the simulation of such a constraint impulses are computed and applied to the particles of the assigned tetrahedrons. The algorithm is easy to implement and ensures exact volume conservation in each simulation step.
A Precalculated Point Set for Caching Shading Information
(The Eurographics Association, 2009) Bikker, Jacco; Reijerse, Roel; P. Alliez and M. Magnor
In this short paper, we present a caching scheme for low-frequent shading information. The scheme consists of a precalculated, carefully constructed sparse set of points, the density of which adapts to local shading requirements, which we estimate by calculating the ambient occlusion. This fixed set of points is then used to store shading information. This shading information is calculated once, or updated prior to rendering each frame. Finally, during rendering, the shading information stored in the point set is used to estimate shading for any point in the scene using interpolation. We apply this scheme to render soft shadows and indirect lighting in a real-time ray traced game environment.
A Gaze-Contingent Display Compensating for Scotomata
(The Eurographics Association, 2009) Duchowski, Andrew T.; Eaddy, Tiras D.; P. Alliez and M. Magnor
A Gaze-Contingent Display (GCD) is developed in GLSL to compensate for scotomata (loss of retinal visual acuity) such as brought on by Age-related Macular Degeneration (AMD). The compensatory GCD introduces a magnification ring slaved to the viewer s gaze point.
Levels of Real-Time Crowd Navigation Behaviour in Urban Environments
(The Eurographics Association, 2009) Haciomeroglu, Murat; Laycock, Robert G.; Day, Andrew M.; P. Alliez and M. Magnor
Continuously increasing interest in real-time crowd simulations motivates researchers from multiple disciplines to investigate more realistic and efficient simulations. Often real-time crowd simulation systems are developed to enhance a user s experience. Therefore, in these applications, most of the computer processing power assigned to the crowd simulation should be given to the agents that will clearly gain a user's attention. This paper investigates methods to improve the computational efficiency of the simulation while not effecting the user s experience. For this reason six dynamically sized areas are defined according to the camera's position and direction. Three types of motion algorithms with different complexities are defined to be used in the different simulation areas. The proposed technique is used to simulate 10000 pedestrians in a 4km2 urban environment and is shown to offer more than 10 times improvement in computational performance.
Real-time Vision-based Lateral Drift Correction
(The Eurographics Association, 2009) Hübner, Thomas; Pajarola, Renato; P. Alliez and M. Magnor
A major drawback in many robotics projects is the dependance on a specific environment and the otherwise uncertain behavior of the hardware. Simple navigation tasks like driving in a straight line can lead to a strong lateral drift over time in an unknown environment. In this paper we propose a fast and simple solution for the lateral drift problem for vision guided robots by real-time scene analysis. Without an environment-specific calibration of the robot s drive system, we balance the differential drive speed on the fly. Therefore, a feature detector is used on consecutive images. Detected feature points determine the focus of expansion (FOE) that is used for locating and correcting the robot s lateral drift. Results are presented for an unmodified real-world indoor environment that demonstrate that our method is able to correct most lateral drift, solely based on real-time vision processing.
Fast Approximation of Multiple Scattering in Inhomogeneous Participating Media
(The Eurographics Association, 2009) Szirmay-Kalos, László; Liktor, Gábor; Umenhoffer, Tamás; Tóth, Balázs; P. Alliez and M. Magnor
This paper presents a fast approximation for the solution of the radiative transfer equation in inhomogeneous participating media. This scheme traces rays from the point light creating spherical wavefronts. While we march on a particular ray, we assume that other rays find similar material properties, which allows the solution of the diffusion equation for this ray. The proposed approximation of the scattered component can be computed in parallel with obtaining the direct term at practically no additional cost. The approximation may be used for direct visualization, an initial guess for an iterative solution, or for the main part of a Monte Carlo solution.
Depth of Field in Plenoptic Cameras
(The Eurographics Association, 2009) Georgiev, Todor; Lumsdaine, Andrew; P. Alliez and M. Magnor
Certain new algorithms used by plenoptic cameras require focused microlens images. The range of applicability of these algorithms therefore depends on the depth of field of the relay system comprising the plenoptic camera. We analyze the relationships and tradeoffs between camera parameters and depth of field and characterize conditions for optimal refocusing, stereo, and 3D imaging.
Bilateral Filter Based Compositing for Variable Exposure Photography
(The Eurographics Association, 2009) Raman, Shanmuganathan; Chaudhuri, Subhasis; P. Alliez and M. Magnor
Compositing a scene from multiple images is of considerable interest to graphics professionals. Typical compositing techniques involve estimation or explicit preparation of matte by an artist. In this article, we address the problem of automatic compositing of a scene from images obtained through variable exposure photography. We consider the High Dynamic Range Imaging (HDRI) problem and review some of the existing approaches for directly generating a Low Dynamic Range (LDR) image from multi-exposure images. We propose a computationally efficient method of scene compositing using edge-preserving filters such as bilateral filters. The key challenge is to composite the multi-exposure images in such a way so as to preserve details in both brightly and poorly illuminated regions of the scene within the limited dynamic range.
A new Projection Method for Point Set Surfaces
(The Eurographics Association, 2009) Kalbe, Thomas; Fuhrmann, Simon; Uhrig, Stefan; Zeilfelder, Frank; Kuijper, Arjan; P. Alliez and M. Magnor
A successful approach in triangulating point set surfaces is to apply operations, like a projection operator for advancing front algorithms, directly to Moving-Least Squares (MLS) surfaces. The MLS method naturally handles noisy input data and is especially useful for point clouds derived from real-world solids. Unfortunately, MLS is computationally extensive and complex. We present a novel projection method that does not require solving a nonlinear optimization problem as MLS does. We create a polynomial approximation of the surface similar to MLS but our method adapts the degree of the polynomial with respect to the points to be approximated. The approximated points are iteratively collected compromising connectivity information. We enhance the orientation of the local coordinate system to further improve the method. The results confirm that our method is more robust and also accelerates triangulation due to a preprocessing step that needs to be done only once per data set.
Importance Sampling with Floyd-Steinberg Halftoning
(The Eurographics Association, 2009) Szirmay-Kalos, László; Szécsi, László; Penzov, Anton; P. Alliez and M. Magnor
This paper proposes a deterministic importance sampling algorithm for complex integrands. The idea is based on the recognition that halftoning algorithms are equivalent to importance sampling if the gray-scale image and a resulting white pixel are considered as the target importance function and the sampling position, respectively. We adopt the Floyd-Steinberg halftoning algorithm, extend it to higher dimensions, and rephrase it as a sampling method. As the Floyd-Steinberg halftoning places a sample also considering where other samples are located, our sampling algorithm distributes samples in a stratified way. In order to demonstrate the power of the method, we present an environment mapping application where the sampling mimics the product of the cosine weighted BRDF, environment radiance, and the environment visibility.
Noise Robust Surface Reconstruction by Combining PU and Graph-cut
(The Eurographics Association, 2009) Nagai, Yukie; Ohtake, Yutaka; Suzuki, Hiromasa; P. Alliez and M. Magnor
We present a novel method of reconstructing surfaces from 3D scattered points by combining Partition of Unity (PU) and a Graph-cut approach. PU is a local approximation technique, meaning that the surfaces obtained have high accuracy but are sensitive to noise. Graph-cut, on the other hand, is a global algorithm that is robust to noise but produces low-accuracy results because it is a discrete binary operation. Our algorithm combines these two methods to achieve robust, high accuracy surface reconstruction. First, a PU implicit function is constructed by covering a space containing a point cloud with spherical supports of linear polynomials. Graph-cut is then performed to separate the covered domain into inside and outside areas of the object to be reconstructed. Finally, we extract the zero-level of PU using the marching tetrahedra approach.
Does Brief Exposure to a Self-avatar Effect Common Human Behaviors in Immersive Virtual Environments?
(The Eurographics Association, 2009) Streuber, Stephan; Rosa, Stephan de la; Trutoiu, Laura; Bülthoff, Heinrich H.; Mohler, Betty J.; P. Alliez and M. Magnor
A plausible assumption is that self-avatars increase the realism of immersive virtual environments (VEs), because self-avatars provide the user with a visual representation of his/her own body. Consequently having a self-avatar might lead to more realistic human behavior in VEs. To test this hypothesis we compared human behavior in VE with and without providing knowledge about a self-avatar with real human behavior in real-space. This comparison was made for three tasks: a locomotion task (moving through the content of the VE), an object interaction task (interacting with the content of the VE), and a social interaction task (interacting with other social entities within the VE). Surprisingly, we did not find effects of a self-avatar exposure on any of these tasks. However, participant s VE and real world behavior differed significantly. These results challenge the claim that knowledge about the self-avatar substantially influences natural human behavior in immersive VEs.

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