31-Issue 2

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https://diglib.eg.org/handle/10.2312/171

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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.
Preface and Table of Contents
(The Eurographics Association and Blackwell Publishing Ltd., 2012) P. Cignoni and T. Ertl
Mesh Colorization
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Leifman, George; Tal, Ayellet; P. Cignoni and T. Ertl
This paper proposes a novel algorithm for colorization of meshes. This is important for applications in which the model needs to be colored by just a handful of colors or when no relevant image exists for texturing the model. For instance, archaeologists argue that the great Roman or Greek statues were full of color in the days of their creation, and traces of the original colors can be found. In this case, our system lets the user scribble some desired colors in various regions of the mesh. Colorization is then formulated as a constrained quadratic optimization problem, which can be readily solved. Special care is taken to avoid color bleeding between regions, through the definition of a new direction field on meshes.
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.
Factored Facade Acquisition using Symmetric Line Arrangements
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Ceylan, Duygu; Mitra, Niloy J.; Li, Hao; Weise, Thibaut; Pauly, Mark; P. Cignoni and T. Ertl
We introduce a novel framework for image-based 3D reconstruction of urban buildings based on symmetry priors. Starting from image-level edges, we generate a sparse and approximate set of consistent 3D lines. These lines are then used to simultaneously detect symmetric line arrangements while refining the estimated 3D model. Operating both on 2D image data and intermediate 3D feature representations, we perform iterative feature consolidation and effective outlier pruning, thus eliminating reconstruction artifacts arising from ambiguous or wrong stereo matches. We exploit non-local coherence of symmetric elements to generate precise model reconstructions, even in the presence of a significant amount of outlier image-edges arising from reflections, shadows, outlier objects, etc. We evaluate our algorithm on several challenging test scenarios, both synthetic and real. Beyond reconstruction, the extracted symmetry patterns are useful towards interactive and intuitive model manipulations.
SMAA: Enhanced Subpixel Morphological Antialiasing
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Jimenez, Jorge; Echevarria, Jose I.; Sousa, Tiago; Gutierrez, Diego; P. Cignoni and T. Ertl
We present a new image-based, post-processing antialiasing technique, which offers practical solutions to the common, open problems of existing filter-based real-time antialiasing algorithms. Some of the new features include local contrast analysis for more reliable edge detection, and a simple and effective way to handle sharp geometric features and diagonal lines. This, along with our accelerated and accurate pattern classification allows for a better reconstruction of silhouettes. Our method shows for the first time how to combine morphological antialiasing (MLAA) with additional multi/supersampling strategies (MSAA, SSAA) for accurate subpixel features, and how to couple it with temporal reprojection; always preserving the sharpness of the image. All these solutions combine synergies making for a very robust technique, yielding results of better overall quality than previous approaches while more closely converging to MSAA/SSAA references but maintaining extremely fast execution times. Additionally, we propose different presets to better fit the available resources or particular needs of each scenario.
Data-Driven Estimation of Cloth Simulation Models
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Miguel, Eder; Bradley, Derek; Thomaszewski, Bernhard; Bickel, Bernd; Matusik, Wojciech; Otaduy, Miguel A.; Marschner, Steve; P. Cignoni and T. Ertl
Progress in cloth simulation for computer animation and apparel design has led to a multitude of deformation models, each with its own way of relating geometry, deformation, and forces. As simulators improve, differences between these models become more important, but it is difficult to choose a model and a set of parameters to match a given real material simply by looking at simulation results. This paper provides measurement and fitting methods that allow nonlinear models to be fit to the observed deformation of a particular cloth sample. Unlike standard textile testing, our system measures complex 3D deformations of a sheet of cloth, not just one-dimensional force-displacement curves, so it works under a wider range of deformation conditions. The fitted models are then evaluated by comparison to measured deformations with motions very different from those used for fitting.
Automatically Rigging Multi-component Characters
(The Eurographics Association and John Wiley and Sons Ltd., 2012) Bharaj, Gaurav; Thormählen, Thorsten; Seidel, Hans-Peter; Theobalt, Christian; P. Cignoni and T. Ertl
Rigging an arbitrary 3D character by creating an animation skeleton is a time-consuming process even for experienced animators. In this paper, we present an algorithm that automatically creates animation rigs for multicomponent 3D models, as they are typically found in online shape databases. Our algorithm takes as input a multi-component model and an input animation skeleton with associated motion data. It then creates a target skeleton for the input model, calculates the rigid skinning weights, and a mapping between the joints of the target skeleton and the input animation skeleton. The automatic approach does not need additional semantic information, such as component labels or user-provided correspondences, and succeeds on a wide range of models where the number of components is significantly different. It implicitly handles large scale and proportional differences between input and target skeletons and can deal with certain morphological differences, e.g., if input and target have different numbers of limbs. The output of our algorithm can be directly used in a retargeting system to create a plausible animated character.
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.

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