EG2012

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https://diglib.eg.org/handle/10.2312/292

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Mapping Images to Target Devices: Spatial, Temporal, Stereo, Tone, and Color
(The Eurographics Association, 2012) Banterle, Francesco; Artusi, Alessandro; Aydin, Tunc O.; Didyk, Piotr; Eisemann, Elmar; Gutierrez, Diego; Mantiuk, Rafael; Myszkowski, Karol; Ritschel, Tobias; Renato Pajarola and Michela Spagnuolo
Retargeting is a process through which an image or a video is adapted from the display device for which it was meant (target display) to another one (retarget display). The retarget display can have different features from the target one such as: dynamic range, discretization levels, color gamut, multi-view (3D), refresh rate, spatial resolution, etc. This tutorial presents the latest solutions and techniques for retargeting images along various dimensions (such as dynamic range, colors, temporal and spatial resolutions) and offers for the first time a much-needed holistic view of the field. This includes how to measure and analyze the changes applied to an image/video in terms of quality using both (subjective) psychophysical experiments and (objective) computational metrics.
Distance Learning in Computer Graphics
(The Eurographics Association, 2012) Chica, Antoni; Fairén, Marta; Pelechano, Nuria; Giovanni Gallo and Beatriz Sousa Santos
Computer graphic courses are pretty established in most computer graphics degrees worldwide. Distance learning has been gaining popularity as fast internet access from home has been reaching wider areas around the world. If we combine this with the fact that the popularity of video games all over the world has made the technology required for rendering real time graphics widely available and affordable, we have the perfect environment for teaching computer graphics through distance learning universities. In this paper, we explain our experience in teaching Computer Graphics basics for the last 10 years at the distance teaching university Universitat Oberta de Catalunya (UOC). By using materials that include interactive applets which allow the student to play with basic Computer Graphics concepts, we observe that students can understand the course despite the teacher not being present in the learning process.
GPU Texture Level of Abstraction in 3D Scenes
(The Eurographics Association, 2012) Suarez, Jordane; Belhadj, Farès; Boyer, Vincent; Andrea Fusiello and Michael Wimmer
We present a method to dynamically control the texture level of abstraction in 3D scene. Level of abstraction consists in visualizing the necessary and sufficient information in an image. Texture generation is generally realized by a designer in a high resolutions with a low level of abstraction. Our model provides automatically texture level of abstraction through offline and online segmentation and lets the designer define the number of colors in the object texture.
Building a Serious Game to Teach Secure Coding in Introductory Programming Courses
(The Eurographics Association, 2012) Adamo-Villani, Nicoletta; Oania, Marcus; Whittinghill, David; Brown, Jacob; Cooper, Stephen; Giovanni Gallo and Beatriz Sousa Santos
We report the development and initial evaluation of a serious game that, in conjunction with appropriately designed matching laboratory exercises, can be used to teach secure coding and Information Assurance (IA) concepts across a range of introductory computing courses. The IA Game is a role-playing serious game (RPG) in which the student travels through seven computer techno-inspired environments (IA concept rooms); in each environment he/she learns a different IA concept. After playing each level, the student completes a related CS educational module comprised of a theory lesson and a lab assignment. The game is being created with a user-centered iterative approach that includes two forms of evaluation: formative and summative. In this paper we report the findings of an initial formative evaluation of the first 2 game levels with a group of undergraduate students.
A Survey of Urban Reconstruction
(The Eurographics Association, 2012) Musialski, Przemyslaw; Wonka, Peter; Aliaga, Daniel G.; Wimmer, Michael; Gool, Luc van; Purgathofer, Werner; Marie-Paule Cani and Fabio Ganovelli
This paper provides a comprehensive overview of urban reconstruction. While there exists a considerable body of literature, this topic is still under very active research. The work reviewed in this survey stems from the following three research communities: computer graphics, computer vision, and photogrammetry and remote sensing. Our goal is to provide a survey that will help researchers to better position their own work in the context of existing solutions, and to help newcomers and practitioners in computer graphics to quickly gain an overview of this vast field. Further, we would like to bring the mentioned research communities to even more interdisciplinary work, since the reconstruction problem itself is by far not solved.
Realtime 3D Sensor Based Air Flow Reconstruction
(The Eurographics Association, 2012) Dyck, Michiel Van; Peremans, Herbert; Andrea Fusiello and Michael Wimmer
Based on state-of-the art bio-inspired air flow sensors it becomes possible to capture air flow velocity and direction at multiple locations at the same time instance. These sensor values can be used in a simulation environment to visualize and examine the captured air flow pattern. The simulation environment makes interpolations of the flow between the sensors based on the Navier-Stokes equations. These equations can be solved efficiently using a stable approximation technique described by J Stam and making use of the enormous parallel computing power available through the latest graphical processing boards.
Multi-user Immersive 3D Reconstruction Environment
(The Eurographics Association, 2012) Sedlacek, David; Travnicek, Zdenek; Zara, Jiri; Andrea Fusiello and Michael Wimmer
A tool for user driven 3D reconstruction is presented in this poster together with ideas of tool extension for a work in immersive environment with multi-user editing possibility. The main purpose of the tool is cultural heritage and architecture reconstruction with direct visualization.
Procedural Texture Preview
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Lasram, Anass; Lefebvre, Sylvain; Damez, Cyrille; P. Cignoni and T. Ertl
Procedural textures usually require spending time testing parameters to realize the diversity of appearances. This paper introduces the idea of a procedural texture preview: A single static image summarizing in a limited pixel space the appearances produced by a given procedure. Unlike grids of thumbnails our previews present a continuous image of appearances, analog to a map. The main challenge is to ensure that most appearances are visible, are allocated a similar pixel area, and are ordered in a smooth manner throughout the preview. To reach this goal, we introduce a new layout algorithm accounting simultaneously for these criteria. After computing a layout of appearances, we rely on by-example texture synthesis to produce the final preview. We demonstrate our approach on a database of production-level procedural textures.
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.
SHADOWPIX: Multiple Images from Self Shadowing
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Bermano, Amit; Baran, Ilya; Alexa, Marc; Matusik, Wojciech; P. Cignoni and T. Ertl
SHADOWPIX are white surfaces that display several prescribed images formed by the self-shadowing of the surface when lit from certain directions. The effect is surprising and not commonly seen in the real world. We present algorithms for constructing SHADOWPIX that allow up to four images to be embedded in a single surface. SHADOWPIX can produce a variety of unusual effects depending on the embedded images: moving the light can animate or relight the object in the image, or three colored lights may be used to produce a single colored image. SHADOWPIX are easy to manufacture using a 3D printer and we present photographs, videos, and renderings demonstrating these effects.
Importance Caching for Complex Illumination
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Georgiev, Iliyan; Krivánek, Jaroslav; Popov, Stefan; Slusallek, Philipp; P. Cignoni and T. Ertl
Realistic rendering requires computing the global illumination in the scene, and Monte Carlo integration is the best-known method for doing that. The key to good performance is to carefully select the costly integration samples, which is usually achieved via importance sampling. Unfortunately, visibility is difficult to factor into the importance distribution, which can greatly increase variance in highly occluded scenes with complex illumination. In this paper, we present importance caching - a novel approach that selects those samples with a distribution that includes visibility, while maintaining efficiency by exploiting illumination smoothness. At a sparse set of locations in the scene, we construct and cache several types of probability distributions with respect to a set of virtual point lights (VPLs), which notably include visibility. Each distribution type is optimized for a specific lighting condition. For every shading point, we then borrow the distributions from nearby cached locations and use them for VPL sampling, avoiding additional bias. A novel multiple importance sampling framework finally combines the many estimators. In highly occluded scenes, where visibility is a major source of variance in the incident radiance, our approach can reduce variance by more than an order of magnitude. Even in such complex scenes we can obtain accurate and low noise previews with full global illumination in a couple of seconds on a single mid-range CPU.
A Cell-Based Light Interaction Model for Human Blood
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Yim, Daniel; Baranoski, Gladimir V. G.; Kimmel, Brad W.; Chen, T. Francis; Miranda, Erik; P. Cignoni and T. Ertl
The development of predictive appearance models for organic tissues is a challenging task due to the inherent complexity of these materials. In this paper, we closely examine the biophysical processes responsible for the appearance attributes of whole blood, one the most fundamental of these materials. We describe a new appearance model that simulates the mechanisms of light propagation and absorption within the cellular and fluid portions of this specialized tissue. The proposed model employs a comprehensive, and yet flexible first principles approach based on the morphological, optical and biochemical properties of blood cells. This approach allows for environment driven changes in the cells' anatomy and orientation to be appropriately included into the light transport simulations. The correctness and predictive capabilities of the proposed model are quantitatively and qualitatively evaluated through comparisons of modeled results with actual measured data and experimental observations reported in the scientific literature. Its incorporation into rendering systems is illustrated through images of blood samples depicting appearance variations controlled by physiologically meaningful parameters. Besides the contributions to the modeling of material appearance, the research presented in this paper is also expected to have applications in a wide range of biomedical areas, from optical diagnostics to the visualization and noninvasive imaging of blood-perfused tissues.
NoRM: No-Reference Image Quality Metric for Realistic Image Synthesis
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Herzog, Robert; Cadík, Martin; Aydin, Tunç O.; Kim, Kwang In; Myszkowski, Karol; Seidel, Hans-Peter; P. Cignoni and T. Ertl
Synthetically generating images and video frames of complex 3D scenes using some photo-realistic rendering software is often prone to artifacts and requires expert knowledge to tune the parameters. The manual work required for detecting and preventing artifacts can be automated through objective quality evaluation of synthetic images. Most practical objective quality assessment methods of natural images rely on a ground-truth reference, which is often not available in rendering applications. While general purpose no-reference image quality assessment is a difficult problem, we show in a subjective study that the performance of a dedicated no-reference metric as presented in this paper can match the state-of-the-art metrics that do require a reference. This level of predictive power is achieved exploiting information about the underlying synthetic scene (e.g., 3D surfaces, textures) instead of merely considering color, and training our learning framework with typical rendering artifacts. We show that our method successfully detects various non-trivial types of artifacts such as noise and clamping bias due to insufficient virtual point light sources, and shadow map discretization artifacts. We also briefly discuss an inpainting method for automatic correction of detected artifacts.
Linear Analysis of Nonlinear Constraints for Interactive Geometric Modeling
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Habbecke, Martin; Kobbelt, Leif; P. Cignoni and T. Ertl
Thanks to its flexibility and power to handle even complex geometric relations, 3D geometric modeling with nonlinear constraints is an attractive extension of traditional shape editing approaches. However, existing approaches to analyze and solve constraint systems usually fail to meet the two main challenges of an interactive 3D modeling system: For each atomic editing operation, it is crucial to adjust as few auxiliary vertices as possible in order to not destroy the user's earlier editing effort. Furthermore, the whole constraint resolution pipeline is required to run in real-time to enable a fluent, interactive workflow. To address both issues, we propose a novel constraint analysis and solution scheme based on a key observation: While the computation of actual vertex positions requires nonlinear techniques, under few simplifying assumptions the determination of the minimal set of to-be-updated vertices can be performed on a linearization of the constraint functions. Posing the constraint analysis phase as the solution of an under-determined linear system with as few non-zero elements as possible enables us to exploit an efficient strategy for the Cardinality Minimization problem known from the field of Compressed Sensing, resulting in an algorithm capable of handling hundreds of vertices and constraints in real-time. We demonstrate at the example of an image-based modeling system for architectural models that this approach performs very well in practical applications.
crdbrd: Shape Fabrication by Sliding Planar Slices
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Hildebrand, Kristian; Bickel, Bernd; Alexa, Marc; P. Cignoni and T. Ertl
We introduce an algorithm and representation for fabricating 3D shape abstractions using mutually intersecting planar cut-outs. The planes have prefabricated slits at their intersections and are assembled by sliding them together. Often such abstractions are used as a sculptural art form or in architecture and are colloquially called 'cardboard sculptures'. Based on an analysis of construction rules, we propose an extended binary space partitioning tree as an efficient representation of such cardboard models which allows us to quickly evaluate the feasibility of newly added planar elements. The complexity of insertion order quickly increases with the number of planar elements and manual analysis becomes intractable. We provide tools for generating cardboard sculptures with guaranteed constructibility. In combination with a simple optimization and sampling strategy for new elements, planar shape abstraction models can be designed by iteratively adding elements. As an output, we obtain a fabrication plan that can be printed or sent to a laser cutter. We demonstrate the complete process by designing and fabricating cardboard models of various well-known 3D shapes.
Explicit Mesh Surfaces for Particle Based Fluids
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Yu, Jihun; Wojtan, Chris; Turk, Greg; Yap, Chee; P. Cignoni and T. Ertl
We introduce the idea of using an explicit triangle mesh to track the air/fluid interface in a smoothed particle hydrodynamics (SPH) simulator. Once an initial surface mesh is created, this mesh is carried forward in time using nearby particle velocities to advect the mesh vertices. The mesh connectivity remains mostly unchanged across time-steps; it is only modified locally for topology change events or for the improvement of triangle quality. In order to ensure that the surface mesh does not diverge from the underlying particle simulation, we periodically project the mesh surface onto an implicit surface defined by the physics simulation. The mesh surface gives us several advantages over previous SPH surface tracking techniques. We demonstrate a new method for surface tension calculations that clearly outperforms the state of the art in SPH surface tension for computer graphics. We also demonstrate a method for tracking detailed surface information (like colors) that is less susceptible to numerical diffusion than competing techniques. Finally, our temporally-coherent surface mesh allows us to simulate highresolution surface wave dynamics without being limited by the particle resolution of the SPH simulation.
Realistic Following Behaviors for Crowd Simulation
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Lemercier, Samuel; Jelic, Asja; Kulpa, Richard; Hua, Jiale; Fehrenbach, Jérôme; Degond, Pierre; Appert-Rolland, Cécile; Donikian, Stéphane; Pettré, Julien; P. Cignoni and T. Ertl
While walking through a crowd, a pedestrian experiences a large number of interactions with his neighbors. The nature of these interactions is varied, and it has been observed that macroscopic phenomena emerge from the combination of these local interactions. Crowd models have hitherto considered collision avoidance as the unique type of interactions between individuals, few have considered walking in groups. By contrast, our paper focuses on interactions due to the following behaviors of pedestrians. Following is frequently observed when people walk in corridors or when they queue. Typical macroscopic stop-and-go waves emerge under such traffic conditions. Our contributions are, first, an experimental study on following behaviors, second, a numerical model for simulating such interactions, and third, its calibration, evaluation and applications. Through an experimental approach, we elaborate and calibrate a model from microscopic analysis of real kinematics data collected during experiments. We carefully evaluate our model both at the microscopic and the macroscopic levels. We also demonstrate our approach on applications where following interactions are prominent.
Repetition Maximization based Texture Rectification
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Aiger, Dror; Cohen-Or, Daniel; Mitra, Niloy J.; P. Cignoni and T. Ertl
Many photographs are taken in perspective. Techniques for rectifying resulting perspective distortions typically rely on the existence of parallel lines in the scene. In scenarios where such parallel lines are hard to automatically extract or manually annotate, the unwarping process remains a challenge. In this paper, we introduce an automatic algorithm to rectifying images containing textures of repeated elements lying on an unknown plane. We unwrap the input by maximizing for image self-similarity over the space of homography transformations. We map a set of detected regional descriptors to surfaces in a transformation space, compute the intersection points among triplets of such surfaces, and then use consensus among the projected intersection points to extract the correcting transform. Our algorithm is global, robust, and does not require explicit or accurate detection of similar elements. We evaluate our method on a variety of challenging textures and images. The rectified outputs are directly useful for various tasks including texture synthesis, image completion, etc.
Manufacturing Layered Attenuators for Multiple Prescribed Shadow Images
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Baran, Ilya; Keller, Philipp; Bradley, Derek; Coros, Stelian; Jarosz, Wojciech; Nowrouzezahrai, Derek; Gross, Markus; P. Cignoni and T. Ertl
We present a practical and inexpensive method for creating physical objects that cast different color shadow images when illuminated by prescribed lighting configurations. The input to our system is a number of lighting configurations and corresponding desired shadow images. Our approach computes attenuation masks, which are then printed on transparent materials and stacked to form a single multi-layer attenuator. When illuminated with the input lighting configurations, this multi-layer attenuator casts the prescribed color shadow images. Alternatively, our method can compute layers so that their permutations produce different prescribed shadow images under fixed lighting. Each multi-layer attenuator is quick and inexpensive to produce, can generate multiple full-color shadows, and can be designed to respond to different types of natural or synthetic lighting setups. We illustrate the effectiveness of our multi-layer attenuators in simulation and in reality, with the sun as a light source.
Steady State Stokes Flow Interpolation for Fluid Control
(The Eurographics Association, 2012) Bhatacharya, Haimasree; Nielsen, Michael B.; Bridson, Robert; Carlos Andujar and Enrico Puppo
Fluid control methods often require surface velocities interpolated throughout the interior of a shape to use the velocity as a feedback force or as a boundary condition. Prior methods for interpolation in computer graphics velocity extrapolation in the normal direction and potential flow suffer from a common problem. They fail to capture the rotational components of the velocity field, although extrapolation in the normal direction does consider the tangential component. We address this problem by casting the interpolation as a steady state Stokes flow. This type of flow captures the rotational components and is suitable for controlling liquid animations where tangential motion is pronounced, such as in a breaking wave.

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