EG2012

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S-buffer: Sparsity-aware Multi-fragment Rendering
(The Eurographics Association, 2012) Vasilakis, Andreas A.; Fudos, Ioannis; Carlos Andujar and Enrico Puppo
This work introduces S-buffer, an efficient and memory-friendly gpu-accelerated A-buffer architecture for multifragment rendering. Memory is organized into variable contiguous regions for each pixel, thus avoiding limitations set in linked-lists and fixed-array techniques. S-buffer exploits fragment distribution for precise allocation of the needed storage and pixel sparsity (empty pixel ratio) for computing the memory offsets for each pixel in a parallel fashion. An experimental comparative evaluation of our technique over previous multi-fragment rendering approaches in terms of memory and performance is provided.
How Not to Be Seen -- Object Removal from Videos of Crowded Scenes
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Granados, Miguel; Tompkin, James; Kim, Kwang In; Grau, Oliver; Kautz, Jan; Theobalt, Christian; P. Cignoni and T. Ertl
Removing dynamic objects from videos is an extremely challenging problem that even visual effects professionals often solve with time-consuming manual frame-by-frame editing. We propose a new approach to video completion that can deal with complex scenes containing dynamic background and non-periodical moving objects. We build upon the idea that the spatio-temporal hole left by a removed object can be filled with data available on other regions of the video where the occluded objects were visible. Video completion is performed by solving a large combinatorial problem that searches for an optimal pattern of pixel offsets from occluded to unoccluded regions. Our contribution includes an energy functional that generalizes well over different scenes with stable parameters, and that has the desirable convergence properties for a graph-cut-based optimization. We provide an interface to guide the completion process that both reduces computation time and allows for efficient correction of small errors in the result. We demonstrate that our approach can effectively complete complex, high-resolution occlusions that are greater in difficulty than what existing methods have shown.
Recent Advances in Real-Time Collision and Proximity Computations for Games and Simulations
(The Eurographics Association, 2012) Frye, Stephen; Harada, Takahiro; Kim, Young J.; Yoon, Sung-eui; Renato Pajarola and Michela Spagnuolo
This course is intended for instructing students and practitioners on recent developments related to collision and proximity computations for interactive games and simulations. There have been significant advances in various physics-based simulation techniques for movies, interactive games, and virtual environments. Most recent work has been on achieving realistic simulations of rigid, articulated, deforming, and fracturing models. However, many complex and challenging simulations (e.g., fracturing simulation) are not widely used in interactive games because of their computational requirements, although the hardware capability of current CPUs and GPUs has considerably improving. It is well known that one of the main performance bottlenecks in most simulations lies in proximity queries including collision detection, minimum separation distance, and penetration depth computations. As a result, there has been significant recent research on developing real-time proximity computation algorithms for interactive games and high-quality simulations. Some of recent advanced techniques are able to achieve interactive performance even for most challenging simulations such as fracturing or large-scale cloth simulations. However, these techniques are quite complicated. Moreover, they require in-depth geometric background and sophisticated optimizations on multi-core architectures. These techniques, therefore, have not been easily accessible to students and practitioners who work on real-time simulation methods. Our objective is to introduce and teach students and practitioners about efficient proximity computation methods and their practical implementations. By doing so, we can expose the attendees to the latest developments, to bridge the gap between the two different fields: proximity computation and simulation. At a broad level, this course will cover the following topics: Basic algorithms for various proximity queries including collision detection, minimum separation distances, penetration depth, etc.; Discrete and continuous algorithms for rigid, articulated, deforming, and fracturing models. Parallel algorithms that utilize many cores of CPUs, GPUs, or CPUs/GPUs. Applications of various proximity queries in Havoc, a widely used Physics simulation package. Optimized proximity data structures for many-core architectures including GPU. Integrating proximity computation algorithms into physically-based simulation systems. We have four instructors from academia and industry, each of who has significant experiences in designing and implementing different aspects of the aforementioned teaching materials. Since each instructor is a world-class expert in his field, students will receive the best instruction. Moreover, students and practitioners can learn how the industry-leading physics systems benefits from efficient proximity queries.
Unstructured Light Fields
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Davis, Abe; Levoy, Marc; Durand, Fredo; P. Cignoni and T. Ertl
We present a system for interactively acquiring and rendering light fields using a hand-held commodity camera. The main challenge we address is assisting a user in achieving good coverage of the 4D domain despite the challenges of hand-held acquisition. We define coverage by bounding reprojection error between viewpoints, which accounts for all 4 dimensions of the light field. We use this criterion together with a recent Simultaneous Localization and Mapping technique to compute a coverage map on the space of viewpoints. We provide users with real-time feedback and direct them toward under-sampled parts of the light field. Our system is lightweight and has allowed us to capture hundreds of light fields. We further present a new rendering algorithm that is tailored to the unstructured yet dense data we capture. Our method can achieve piecewise-bicubic reconstruction using a triangulation of the captured viewpoints and subdivision rules applied to reconstruction weights.
Digital Archiving of Large 3D Woven Cultural Artifacts
(The Eurographics Association, 2012) Wakita, Wataru; Tanaka, Hiromi T.; Andrea Fusiello and Michael Wimmer
Recently, research on digital museums received increased attention. We have worked on the digital archiving of the Gion Festival in Kyoto , focused on the culture of Kyoto, and developed a realtime and direct-touch interaction system for the 3D woven cultural artifact with haptic interface. After the Gion Festival of 2011, the repair work of the Fune-hoko storage was scheduled. Therefore, we created a 3D measurement system for the large 3D woven cultural artifacts with the laser range scanner, and tried to measure and model the 3D woven cultural artifact of the Fune-hoko at high definition in 3D. Most woven cultural artifact of the Fune-hoko is composed of gold thread, glass, cotton, and brilliant embroidery. Thus, 3D measurement is not easy. Therefore, we arbitrarily changed the laser strength according to the material of the fabric and modeled based on the point-based for the real-time rendering. As a result, we could generate the 3D woven cultural artifact models at high definition.
A Pipeline for Procedural Modelling from Geospatial Data
(The Eurographics Association, 2012) Jesus, Diego; Coelho, António; Rebelo, C.; Cardoso, A.; Sousa, A. A.; Andrea Fusiello and Michael Wimmer
Virtual urban environments can be used for purposes like municipality planning and management. Due to the complexity and large extent of these environments procedural modelling techniques can be used to generate these 3D environments automatically. However these methods need large amounts of spatial data, that is generally available through Geographic Information Systems (GIS). This paper presents a pipeline to integrate semantics and GIS data into the procedural modelling techniques used to recreate virtual urban environments. GIS data can already be used in procedural modelling tools but it does not incorporate semantic information. As such, this pipeline is capable of transforming semantic and geometric data contained in GIS into three dimensional models that represent such urban spaces.
Reflective Shadow Map Clustering for Real-Time Global Illumination
(The Eurographics Association, 2012) Prutkin, Roman; Kaplanyan, Anton; Dachsbacher, Carsten; Carlos Andujar and Enrico Puppo
We present a method for real-time clustering of VPLs obtained from Reflective Shadow Maps (RSM). The clusters are treated as area light sources and used to approximate indirect illumination. The spatial extent of a cluster is used to deduce the shape and size of the respective area light source. Our method is fully GPU-based and avoids flickering by temporally coherent reinitialization of the clustering. It also incorporates importance sampling for view-dependent clustering. We show visually indistinguishable results of indirect illumination with only a fraction of secondary light sources.
Crowd Light: Evaluating the Perceived Fidelity of Illuminated Dynamic Scenes
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Jarabo, Adrian; Eyck, Tom Van; Sundstedt, Veronica; Bala, Kavita; Gutierrez, Diego; O'Sullivan, Carol; P. Cignoni and T. Ertl
Rendering realistic illumination effects for complex animated scenes with many dynamic objects or characters is computationally expensive. Yet, it is not obvious how important such accurate lighting is for the overall perceived realism in these scenes. In this paper, we present a methodology to evaluate the perceived fidelity of illumination in scenes with dynamic aggregates, such as crowds, and explore several factors which may affect this perception. We focus in particular on evaluating how a popular spherical harmonics lighting method can be used to approximate realistic lighting of crowds. We conduct a series of psychophysical experiments to explore how a simple approach to approximating global illumination, using interpolation in the temporal domain, affects the perceived fidelity of dynamic scenes with high geometric, motion, and illumination complexity. We show that the complexity of the geometry and temporal properties of the crowd entities, the motion of the aggregate as a whole, the type of interpolation (i.e., of the direct and/or indirect illumination coefficients), and the presence or absence of colour all affect perceived fidelity. We show that high (i.e., above 75%) levels of perceived scene fidelity can be maintained while interpolating indirect illumination for intervals of up to 30 frames, resulting in a greater than three-fold rendering speed-up
Creating Picture Legends for Group Photos
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Gao, Junhong; Kim, Seon Joo; Brown, Michael S.; P. Cignoni and T. Ertl
Group photos are one of the most common types of digital images found in personal image collections and on social networks. One typical post-processing task for group photos is to produce a key or legend to identify the people in the photo. This is most often done using simple bounding boxes. A more professional approach is to create a picture legend that uses either a full or partial silhouette to identify the individuals. This paper introduces an efficient method for producing picture legends for group photos. Our approach combines face detection with human shape priors into an interactive selection framework to allow users to quickly segment the individuals in a group photo. Our results are better than those obtained by general selection tools and can be produced in a fraction of the time.
Revision Control Framework for 3D Assets
(The Eurographics Association, 2012) Dobos, Jozef; Steed, Anthony; Andrea Fusiello and Michael Wimmer
We propose a non-linear concurrent revision control for centralised management of 3D assets and a novel approach to mesh differencing. Large models are decomposed into individual scene graph (SG) nodes through an asset import library and become versioned as collections of polymorphic documents in a NoSQL database (DB). Well-known operations such as 2- and 3-way diff and merging are supported via a custom DB front-end. By not relying on the knowledge of user edits, we make sure our system works with a range of editing software. We demonstrate the feasibility of our proposal on concurrent 3D editing and conflict resolution.
TECHNI Photons: Evolution of a Course in Data Structures
(The Eurographics Association, 2012) Duchowski, Andrew T.; Giovanni Gallo and Beatriz Sousa Santos
This paper presents the evolution of a data structures and algorithms course based on a specific computer graphics problem, namely photon mapping, as the teaching medium. The paper reports development of the course through several iterations and evaluations, dating back five years. The course originated as a problem-based graphics course requiring sophomore students to implement Hoppe et al. s algorithm for surface reconstruction from unorganized points found in their SIGGRAPH 92 paper of the same title. Although the solution to this problem lends itself well to an exploration of data structures and code modularization, both of which are traditionally taught in early computer science courses, the algorithm s complexity was reflected in students overwhelmingly negative evaluations. Subsequently, because implementation of the kd-tree was seen as the linchpin data structure, it was again featured in the problem of ray tracing trees consisting of more than 250,000,000 triangles. Eventually, because the tree rendering was thought too specific a problem, the photon mapper was chosen as the semester-long problem considered to be a suitable replacement. This paper details the resultant course description and outline, from its now two semesters of teaching.
Real-Time Disparity Map-Based Pictorial Depth Cue Enhancement
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Rößing, Christoph; Hanika, Johannes; Lensch, Hendrik; P. Cignoni and T. Ertl
The availability of stereoscopic image material is increasing rapidly. In contrast to the generation of distance information, displaying it is still a challenging task. To overcome the need for special 3D display hardware, we present a novel real-time video processing framework-based on edge-avoiding à trous wavelets. The framework adds and emphasizes monocular depth cues corresponding to the depth information of a supplemental disparity map. This creates a compelling depth sensation on 2D display devices. The framework enhances multiple depth cues in parallel, such as depth of field, local contrast, ambient occlusion and saturation. At the same time, it improves the disparity map quality. Depth cues control how a human explores an image, since the perception of distance is coupled to visual attention. The presented work demonstrates the effectiveness of the proposed framework in guiding the viewer, without destroying the image content, by evaluating the performance in searchand- find tasks. A user study analyzes the connection between faster response times and the boosting of particular monocular depth cues.
Perceptually Linear Parameter Variations
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Lindow, Norbert; Baum, Daniel; Hege, Hans-Christian; P. Cignoni and T. Ertl
Most visual analysis tasks require interactive adjustment of parameter values. In general, a linear variation of a parameter, using for instance a GUI slider, changes the visual result in a perceptually non-linear way. This hampers interactive adjustment of parameters, especially in regions where rapid perceptual changes occur. Selecting a good parameter value therefore remains a time-consuming and often difficult task. We propose a novel technique to build a non-linear function that maps a new parameter to the original parameter. By prefixing this function to the original parameter and using the new parameter as input, a linear relationship between input and visual feedback is obtained. To construct the non-linear function, we measure the variation of the visual result using image metrics. Given a suitable perceptual image metric, perceptually linear image variations are achieved. We demonstrate the practical utility of our approach by implementing two common image metrics, a perceptual and a non-perceptual one, and by applying the method to a few visual analysis tasks.
Pixel Art with Refracted Light by Rearrangeable Sticks
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Yue, Yonghao; Iwasaki, Kei; Chen, Bing-Yu; Dobashi, Yoshinori; Nishita, Tomoyuki; P. Cignoni and T. Ertl
Pixel art is a kind of digital art that through per-pixel manipulation enables production of a diverse array of artistic images. In this paper, we present a new way for people to experience and express pixel art. Our digital art consists of a set of sticks made of acrylate resin, each of which refracts light from a parallel light source, in certain directions. Artistic users are able to easily rearrange these sticks and view their digital art through the refracted light projection on any planar surface. As we demonstrate in this paper, a user can generate various artistic images using only a single set of sticks. We additionally envision that our pixel art with rearrangeable sticks would have great entertainment appeal, e.g., as an art puzzle.
Teaching 3D Acquisition for Cultural Heritage: a Theory and Practice Approach
(The Eurographics Association, 2012) Dellepiane, Matteo; Scopigno, Roberto; Giovanni Gallo and Beatriz Sousa Santos
The paper presents the experience of a course (3D Graphics for Cultural Heritage) in the context of Humanistic Informatics degree. The goal of the course was to present an overview of the techniques for the acquisition of 3D models of real objects. The focus was put on freeware/open source solutions that could give the students the possibility to experiment directly on the data, and possibly apply them in their future activities. The acquisition techniques were divided in three groups: 3D scanning, Dense Stereo Reconstruction and Re- Lightable Images. Moreover, general concepts about 3D Graphics, remote visualization, and planning of projects were part of the subjects. The final project for each student consisted in a practical acquisition of a real objects, using one of the proposed techniques. The results of the projects showed that high quality 3D acquisition is now possible even with low-cost devices and freeware tools, and that it can be a strongpoint for the career of future young CH professionals.
Interactive Simulation of Rigid Body Dynamics in Computer Graphics
(The Eurographics Association, 2012) Bender, Jan; Erleben, Kenny; Trinkle, Jeff; Coumans, Erwin; Marie-Paule Cani and Fabio Ganovelli
Interactive rigid body simulation is an important part of many modern computer tools. No authoring tool nor a game engine can do without. The high performance computer tools open up new possibilities for changing how designers, engineers, modelers and animators work with their design problems. This paper is a self contained state-of-the-art report on the physics, the models, the numerical methods and the algorithms used in interactive rigid body simulation all of which has evolved and matured over the past 20 years. The paper covers applications and the usage of interactive rigid body simulation. Besides the mathematical and theoretical details that this paper communicates in a pedagogical manner the paper surveys common practice and reflects on applications of interactive rigid body simulation. The grand merger of interactive and off-line simulation methods is imminent, multi-core is everyman s property. These observations pose future challenges for research which we reflect on. In perspective several avenues for possible future work is touched upon such as more descriptive models and contact point generation problems. This paper is not only a stake in the sand on what has been done, it also seeks to give newcomers practical hands on advices and reflections that can give experienced researchers afterthought for the future.
A Computational Model of Afterimages
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Ritschel, Tobias; Eisemann, Elmar; P. Cignoni and T. Ertl
Afterimages are optical illusions, particularly well perceived when fixating an image for an extended period of time and then looking at a neutral background, where an inverted copy of the original stimulus appears. The full mechanism that produces the perceived specific colors and shapes is complex and not entirely understood, but most of the important attributes can be well explained by bleaching of retinal photoreceptors (retinal kinetics). We propose a model to compute afterimages that allows us to simulate their temporal, color and time-frequency behavior. Using this model, high dynamic range (HDR) content can be processed to add realistic afterimages to low dynamic range (LDR) media. Hereby, our approach helps in conveying the original source's luminance and contrast. It can be applied in real-time on full-HD HDR content using standard graphics hardware. Finally, our approach is validated in a perceptual study.
A Simple Algorithm for Maximal Poisson-Disk Sampling in High Dimensions
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Ebeida, Mohamed S.; Mitchell, Scott A.; Patney, Anjul; Davidson, Andrew A.; Owens, John D.; P. Cignoni and T. Ertl
We provide a simple algorithm and data structures for d-dimensional unbiased maximal Poisson-disk sampling. We use an order of magnitude less memory and time than the alternatives. Our results become more favorable as the dimension increases. This allows us to produce bigger samplings. Domains may be non-convex with holes. The generated point cloud is maximal up to round-off error. The serial algorithm is provably bias-free. For an output sampling of size n in fixed dimension d, we use a linear memory budget and empirical O(n) runtime. No known methods scale well with dimension, due to the ''curse of dimensionality.'' The serial algorithm is practical in dimensions up to 5, and has been demonstrated in 6d. We have efficient GPU implementations in 2d and 3d. The algorithm proceeds through a finite sequence of uniform grids. The grids guide the dart throwing and track the remaining disk-free area. The top-level grid provides an efficient way to test if a candidate dart is disk-free. Our uniform grids are like quadtrees, except we delay splits and refine all leaves at once. Since the quadtree is flat it can be represented using very little memory: we just need the indices of the active leaves and a global level. Also it is very simple to sample from leaves with uniform probability.
Interactive Coherence-Based Façade Modeling
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Musialski, Przemyslaw; Wimmer, Michael; Wonka, Peter; P. Cignoni and T. Ertl
We propose a novel interactive framework for modeling building façades from images. Our method is based on the notion of coherence-based editing which allows exploiting partial symmetries across the façade at any level of detail. The proposed workflow mixes manual interaction with automatic splitting and grouping operations based on unsupervised cluster analysis. In contrast to previous work, our approach leads to detailed 3d geometric models with up to several thousand regions per façade. We compare our modeling scheme to others and evaluate our approach in a user study with an experienced user and several novice users.
Quad Meshing
(The Eurographics Association, 2012) Bommes, David; Lévy, Bruno; Pietroni, Nico; Puppo, Enrico; Silva, Claudio; Tarini, Marco; Zorin, Denis; Marie-Paule Cani and Fabio Ganovelli
Triangle meshes have been nearly ubiquitous in computer graphics, and a large body of data structures and geometry processing algorithms based on them has been developed in the literature. At the same time, quadrilateral meshes, especially semi-regular ones, have advantages for many applications, and significant progress was made in quadrilateral mesh generation and processing during the last several years. In this State of the Art Report, we discuss the advantages and problems of techniques operating on quadrilateral meshes, including surface analysis and mesh quality, simplification, adaptive refinement, alignment with features, parametrization, and remeshing.

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