EG2014

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https://diglib.eg.org/handle/10.2312/7703

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Dynamic 2D/3D Registration
(The Eurographics Association, 2014) Bouaziz, Sofien; Tagliasacchi, Andrea; Pauly, Mark; Nicolas Holzschuch and Karol Myszkowski
Image and geometry registration algorithms are an essential component of many computer graphics and computer vision systems. With recent technological advances in RGB-D sensors, such as the Microsoft Kinect or Asus Xtion Live, robust algorithms that combine 2D image and 3D geometry registration have become an active area of research. The goal of this course is to introduce the basics of 2D/3D registration algorithms and to provide theoretical explanations and practical tools to design computer vision and computer graphics systems based on RGB-D devices. To illustrate the theory and demonstrate practical relevance, we briefly discuss three applications: rigid scanning, non-rigid modeling, and realtime face tracking. Our course targets researchers and computer graphics practitioners with a background in computer graphics and/or computer vision. An up-to-date version of the course notes as well as slides and source code can be found at http://lgg.epfl.ch/2d3dRegistration.
Post-Tessellation Geometry Caches
(The Eurographics Association, 2014) Sathe, Rahul; Foley, Tim; Salvi, Marco; Eric Galin and Michael Wand
Current 3D rendering architectures support adaptive tessellation of patches, allowing for increased geometric detail. Patches are specified independently, giving the implementation freedom to exploit parallel execution. However, this independence leads to redundant shading computations at patch corners and along edges. In this paper, we present post-tessellation geometry caches, the edge cache and corner cache, that can reduce redundant shading along patch edges and corners, respectively. We demonstrate the two caches in a software-simulated D3D11 rendering pipeline, and show that for current tessellation workloads our approach saves up to 37% of post-tessellation vertex shading using caches with as few as 8 entries.
Efficient Sorting and Searching in Rendering Algorithms
(The Eurographics Association, 2014) Havran, Vlastimil; Bittner, Jiri; Nicolas Holzschuch and Karol Myszkowski
In the tutorial we show the connection between rendering algorithms and sorting and searching as classical problems studied in computer science. We provide both theoretical and empirical evidence that for many rendering techniques most time is spent by sorting and searching. In particular we discuss problems and solutions for visibility computation, density estimation, and importance sampling. For each problem we mention its specific issues such as dimensionality of the search domain or online versus offline searching. We will present the underlying data structures and their enhancements in the context of specific rendering algorithms such as ray tracing, photon mapping, and hidden surface removal.
The Four I's Recipe for Cooking Up Computer Graphics Exercises and Assessments
(The Eurographics Association, 2014) Peters, Christopher E.; Anderson, Eike Falk; Jean-Jacques Bourdin and Joaquim Jorge and Eike Anderson
The design of meaningful student activities, such as lab exercises and assignments, is a core element of computer graphics pedagogy. Here, we briefly describe our efforts towards making the process of defining and structuring computer graphics activities more explicit. We focus on four main activity categories that are building blocks for practical course design: Independent, Iterative, Incremental and Integrative. These ``Four I's'' of computer graphics activity provide the fundamental ingredients for explicitly defining the design of activity-oriented computer graphics courses with the potential to deliver significant artefacts that may, for example, constitute a portfolio of work for assessment or presentation to employers. The categorisations are intended as the first steps towards more clearly structuring and communicating exercise specifications in collaborative course development settings.
Accurate and Efficient Lighting for Skinned Models
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Tarini, Marco; Panozzo, Daniele; Sorkine-Hornung, Olga; B. Levy and J. Kautz
In the context of real-time, GPU-based rendering of animated skinned meshes, we propose a new algorithm to compute surface normals with minimal overhead both in terms of the memory footprint and the required per-vertex operations. By accounting for the variation of the skinning weights over the surface, we achieve a higher visual quality compared to the standard approximation ubiquitously used in video-game engines and other real-time applications. Our method supports Linear Blend Skinning and Dual Quaternion Skinning. We demonstrate the advantages of our technique on a variety of datasets and provide a complete open-source implementation, including GLSL shaders.
Optimizing Stereo-to-Multiview Conversion for Autostereoscopic Displays
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Chapiro, Alexandre; Heinzle, Simon; Aydin, Tunç Ozan; Poulakos, Steven; Zwicker, Matthias; Smolic, Aljosa; Gross, Markus; B. Levy and J. Kautz
We present a novel stereo-to-multiview video conversion method for glasses-free multiview displays. Different from previous stereo-to-multiview approaches, our mapping algorithm utilizes the limited depth range of autostereoscopic displays optimally and strives to preserve the scene s artistic composition and perceived depth even under strong depth compression. We first present an investigation of how perceived image quality relates to spatial frequency and disparity. The outcome of this study is utilized in a two-step mapping algorithm, where we (i) compress the scene depth using a non-linear global function to the depth range of an autostereoscopic display, and (ii) enhance the depth gradients of salient objects to restore the perceived depth and salient scene structure. Finally, an adapted image domain warping algorithm is proposed to generate the multiview output, which enables overall disparity range extension.
CSG Feature Trees from Engineering Sketches of Polyhedral Shapes
(The Eurographics Association, 2014) Plumed, Raquel; Company, Pedro; Varley, Peter A. C.; Martin, Ralph R.; Eric Galin and Michael Wand
We give a method to obtain a 3D CSG model from a 2D engineering wireframe sketch which depicts a polyhedral shape. The method finds a CSG feature tree compatible with a reverse design history of a 2D line-drawing obtained by vectorising the sketch. The process used seeks the CSG feature tree recursively, combining all design or manufacturing features embedded in the sketch, proceeding in reverse order from the most detailed features to the blank.
Interactive Motion Mapping for Real-time Character Control
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Rhodin, Helge; Tompkin, James; Kim, Kwang In; Varanasi, Kiran; Seidel, Hans-Peter; Theobalt, Christian; B. Levy and J. Kautz
Abstract It is now possible to capture the 3D motion of the human body on consumer hardware and to puppet in real time skeleton-based virtual characters. However, many characters do not have humanoid skeletons. Characters such as spiders and caterpillars do not have boned skeletons at all, and these characters have very different shapes and motions. In general, character control under arbitrary shape and motion transformations is unsolved - how might these motions be mapped? We control characters with a method which avoids the rigging-skinning pipeline - source and target characters do not have skeletons or rigs. We use interactively-defined sparse pose correspondences to learn a mapping between arbitrary 3D point source sequences and mesh target sequences. Then, we puppet the target character in real time. We demonstrate the versatility of our method through results on diverse virtual characters with different input motion controllers. Our method provides a fast, flexible, and intuitive interface for arbitrary motion mapping which provides new ways to control characters for real-time animation.
Coded Exposure HDR Light-Field Video Recording
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Schedl, David C.; Birklbauer, Clemens; Bimber, Oliver; B. Levy and J. Kautz
Capturing exposure sequences to compute high dynamic range (HDR) images causes motion blur in cases of camera movement. This also applies to light-field cameras: frames rendered from multiple blurred HDR lightfield perspectives are also blurred. While the recording times of exposure sequences cannot be reduced for a single-sensor camera, we demonstrate how this can be achieved for a camera array. Thus, we decrease capturing time and reduce motion blur for HDR light-field video recording. Applying a spatio-temporal exposure pattern while capturing frames with a camera array reduces the overall recording time and enables the estimation of camera movement within one light-field video frame. By estimating depth maps and local point spread functions (PSFs) from multiple perspectives with the same exposure, regional motion deblurring can be supported. Missing exposures at various perspectives are then interpolated.
Latency Considerations of Depth-first GPU Ray Tracing
(The Eurographics Association, 2014) Guthe, Michael; Eric Galin and Michael Wand
Despite the potential divergence of depth-first ray tracing [AL09], it is nevertheless the most efficient approach on massively parallel graphics processors. Due to the use of specialized caching strategies that were originally developed for texture access, it has been shown to be compute rather than bandwidth limited. Especially with recents developments however, not only the raw bandwidth, but also the latency for both memory access and read after write register dependencies can become a limiting factor. In this paper we will analyze the memory and instruction dependency latencies of depth first ray tracing. We will show that ray tracing is in fact latency limited on current GPUs and propose three simple strategies to better hide the latencies. This way, we come significantly closer to the maximum performance of the GPU.
Using Modern Interaction Devices for HCI and Interaction Design Courses
(The Eurographics Association, 2014) Hernández, Benjamín; Alvarado, Adriana; Jean-Jacques Bourdin and Joaquim Jorge and Eike Anderson
Recent dissemination of proprietary and third-party PC drivers and SDKs of advanced console controllers and modern interaction devices has enabled new forms of 3D, tactile and multimodal user interfaces. In this paper, we present an educational methodology which allows students to use modern interaction devices (touch screen, depth sensors, gyroscopes) and programming environments in their projects. We re-design Human Computer Interaction (TI - 2004) and Introduction to Interaction Design (TC - 1015) undergraduate courses offered at the Tecnógico de Monterrey, Mexico City Campus, based on the project based learning (PBL) technique and interaction design process. The students were building their own knowledge through the development of a semester project enabling them to demonstrate, taught, and discussed with each other what they had learned. As a result, students learned up-to-date technologies and applied successfully concepts such as body gesture tracking and recognition, natural user interface design and multimodal interaction into their projects.
Spatio-Temporal Geometry Fusion for Multiple Hybrid Cameras using Moving Least Squares Surfaces
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Kuster, Claudia; Bazin, Jean-Charles; Öztireli, Cengiz; Deng, Teng; Martin, Tobias; Popa, Tiberiu; Gross, Markus; B. Levy and J. Kautz
Multi-view reconstruction aims at computing the geometry of a scene observed by a set of cameras. Accurate 3D reconstruction of dynamic scenes is a key component for a large variety of applications, ranging from special effects to telepresence and medical imaging. In this paper we propose a method based on Moving Least Squares surfaces which robustly and efficiently reconstructs dynamic scenes captured by a calibrated set of hybrid color+depth cameras. Our reconstruction provides spatio-temporal consistency and seamlessly fuses color and geometric information. We illustrate our approach on a variety of real sequences and demonstrate that it favorably compares to state-of-the-art methods.
Flower Reconstruction from a Single Photo
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Yan, Feilong; Gong, Minglun; Cohen-Or, Daniel; Deussen, Oliver; Chen, Baoquan; B. Levy and J. Kautz
We present a semi-automatic method for reconstructing flower models from a single photograph. Such reconstruction is challenging since the 3D structure of a flower can appear ambiguous in projection. However, the flower head typically consists of petals embedded in 3D space that share similar shapes and form certain level of regular structure. Our technique employs these assumptions by first fitting a cone and subsequently a surface of revolution to the flower structure and then computing individual petal shapes from their projection in the photo. Flowers with multiple layers of petals are handled through processing different layers separately. Occlusions are dealt with both within and between petal layers. We show that our method allows users to quickly generate a variety of realistic 3D flowers from photographs and to animate an image using the underlying models reconstructed from our method.
Efficient Enforcement of Hard Articulation Constraints in the Presence of Closed Loops and Contacts
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Tomcin, Robin; Sibbing, Dominik; Kobbelt, Leif; B. Levy and J. Kautz
In rigid body simulation, one must distinguish between contacts (so-called unilateral constraints) and articulations (bilateral constraints). For contacts and friction, iterative solution methods have proven most useful for interactive applications, often in combination with Shock-Propagation in cases with strong interactions between contacts (such as stacks), prioritizing performance and plausibility over accuracy. For articulation constraints, direct solution methods are preferred, because one can rely on a factorization with linear time complexity for tree-like systems, even in ill-conditioned cases caused by large mass-ratios or high complexity. Despite recent advances, combining the advantages of direct and iterative solution methods wrt. performance has proven difficult and the intricacy of articulations in interactive applications is often limited by the convergence speed of the iterative solution method in the presence of closed kinematic loops (i.e. auxiliary constraints) and contacts. We identify common performance bottlenecks in the dynamic simulation of unilateral and bilateral constraints and are able to present a simulation method, that scales well in the number of constraints even in ill-conditioned cases with frictional contacts, collisions and closed loops in the kinematic graph. For cases where many joints are connected to a single body, we propose a technique to increase the sparsity of the positive definite linear system. A solution to these bottlenecks is presented in this paper to make the simulation of a wider range of mechanisms possible in real-time without extensive parameter tuning.
Skeleton-based Joints Position Detection
(The Eurographics Association, 2014) Madaras, Martin; Piovarci, Michal; Kovacovský, Tomás; Mathias Paulin and Carsten Dachsbacher
We present a system for detection of joint positions in scans of articulated models. Our method is based purely on skeletons extracted from scanned point clouds of input models. First, skeletons are extracted from scans and then an estimation of possible matches between skeletons is performed. The matches are evaluated and sorted out. The whole matching process is fully automatic, but some user-driven suggestions can be included. Finally, we pick the best matching of skeletons and create a union-skeleton containing all the nodes from all the skeletons. We find nodes in the union-skeleton with rotation changes higher than the predefined threshold. We take these nodes as joints and visualize them in original scans.
Feedback Control for Rotational Movements in Feature Space
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Borno, Mazen Al; Fiume, Eugene; Hertzmann, A.; Lasa, M. de; B. Levy and J. Kautz
Synthesizing controllers for rotational movements in feature space is an open research problem and is particularly challenging because of the need to precisely regulate the character s global orientation, angular momentum and inertia. This paper presents feature-based controllers for a wide variety of rotational movements, including cartwheels, dives and flips. We show that the controllers can be made robust to large external disturbances by using a time-invariant control scheme. The generality of the control laws is demonstrated by providing examples of the flip controller with different apexes, the diving controller with different heights and styles, the cartwheel controller with different speeds and straddle widths, etc. The controllers do not rely on any input motion or offline optimization.
Self-similarity for Accurate Compression of Point Sampled Surfaces
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Digne, Julie; Chaine, Raphaëlle; Valette, Sébastien; B. Levy and J. Kautz
Most surfaces, be it from a fine-art artifact or a mechanical object, are characterized by a strong self-similarity. This property finds its source in the natural structures of objects but also in the fabrication processes: regularity of the sculpting technique, or machine tool. In this paper, we propose to exploit the self-similarity of the underlying shapes for compressing point cloud surfaces which can contain millions of points at a very high precision. Our approach locally resamples the point cloud in order to highlight the self-similarity of the shape, while remaining consistent with the original shape and the scanner precision. It then uses this self-similarity to create an ad hoc dictionary on which the local neighborhoods will be sparsely represented, thus allowing for a light-weight representation of the total surface. We demonstrate the validity of our approach on several point clouds from finearts and mechanical objects, as well as a urban scene. In addition, we show that our approach also achieves a filtering of noise whose magnitude is smaller than the scanner precision.
Thumbnail Galleries for Procedural Models
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Lienhard, Stefan; Specht, Matthias; Neubert, Boris; Pauly, Mark; Müller, Pascal; B. Levy and J. Kautz
Procedural modeling allows for the generation of innumerable variations of models from a parameterized, conditional or stochastic rule set. Due to the abstractness, complexity and stochastic nature of rule sets, it is often very difficult to have an understanding of the diversity of models that a given rule set defines. We address this problem by presenting a novel system to automatically generate, cluster, rank, and select a series of representative thumbnail images out of a rule set. We introduce a set of view attributes that can be used to measure the suitability of an image to represent a model, and allow for comparison of different models derived from the same rule set. To find the best thumbnails, we exploit these view attributes on images of models obtained by stochastically sampling the parameter space of the rule set. The resulting thumbnail gallery gives a representative visual impression of the procedural modeling potential of the rule set. Performance is discussed by means of a number of distinct examples and compared to state-of-the-art approaches.
Teaching Interactivity: Introducing Design Students to Sensors and Microcontrollers
(The Eurographics Association, 2014) Narahara, Taro; Jean-Jacques Bourdin and Joaquim Jorge and Eike Anderson
This paper presents an educational case study and its pedagogical lessons in the context of design teaching. Smart products, adaptive designs, and intelligent spaces are in the forefront of current artistic discourse. They are critical components in sustainable designs where products monitor their own performance and respond to consumers' real-time needs and environmental factors. In order to prepare students in the design field to be able to present interaction-based ideas more effectively, the author developed a project-based course to produce interactive prototypes using sensors, actuators, and microcontrollers. The author introduces instructions using practical template materials that can demonstrate certain key notions such as feedback and kinematics at the earlier phase of learning while providing minimum yet sufficient fundamental skills and theoretical background on programming and electronics. This strategy allows students to acquire extensible knowledge that does not rely on higher-level software functions or specialized but inflexible plug-ins. Students can reinterpret given materials and modify them to produce custom tools that can realize their original project goals. By presenting methods used in the author's course and conceptual example projects by students, an efficient way to teach relatively complex technical materials without overpowering student creativity and motivation will be offered.
A Nonobscuring Eye Tracking Solution for Wide Field-of-View Head-mounted Displays
(The Eurographics Association, 2014) Stengel, Michael; Grogorick, Steve; Rogge, Lorenz; Magnor, Marcus; Mathias Paulin and Carsten Dachsbacher
We present a solution for integrating a binocular eye tracker into current state-of-the-art lens-based head-mounted displays (HMDs) without affecting the available field-of-view on the display. Estimating the relative eye gaze of the user opens the door for HMDs to a much wider spectrum of virtual reality applications and games. Further, we present a concept of a low-cost head-mounted display with eye tracking and discuss applications which strongly depend on or benefit from gaze estimation.

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