Full Papers 2014 - CGF 33-Issue 2
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Item Pose Partitioning for Multi-resolution Segmentation of Arbitrary Mesh Animations(The Eurographics Association and John Wiley and Sons Ltd., 2014) Vasilakis, Andreas A.; Fudos, Ioannis; B. Levy and J. KautzWe present a complete approach to efficiently deriving a varying level-of-detail segmentation of arbitrary animated objects. An over-segmentation is built by combining sets of initial segments computed for each input pose, followed by a fast progressive simplification which aims at preserving rigid segments. The final segmentation result can be efficiently adjusted for cases where pose editing is performed or new poses are added at arbitrary positions in the mesh animation sequence. A smooth view of pose-to-pose segmentation transitions is offered by merging the partitioning of the current pose with that of the next pose. A perceptually friendly visualization scheme is also introduced for propagating segment colors between consecutive poses.We report on the efficiency and quality of our framework as compared to previous methods under a variety of skeletal and highly deformable mesh animations.Item Parameter Estimation and Comparative Evaluation of Crowd Simulations(The Eurographics Association and John Wiley and Sons Ltd., 2014) Wolinski, David; Guy, Stephen; Olivier, Anne-Helene; Lin, Ming; Manocha, Dinesh; Pettré, Julien; B. Levy and J. KautzWe present a novel framework to evaluate multi-agent crowd simulation algorithms based on real-world observations of crowd movements. A key aspect of our approach is to enable fair comparisons by automatically estimating the parameters that enable the simulation algorithms to best fit the given data. We formulate parameter estimation as an optimization problem, and propose a general framework to solve the combinatorial optimization problem for all parameterized crowd simulation algorithms. Our framework supports a variety of metrics to compare reference data and simulation outputs. The reference data may correspond to recorded trajectories, macroscopic parameters, or artist-driven sketches. We demonstrate the benefits of our framework for example-based simulation, modeling of cultural variations, artist-driven crowd animation, and relative comparison of some widely-used multi-agent simulation algorithms.Item Designing Large-Scale Interactive Traffic Animations for Urban Modeling(The Eurographics Association and John Wiley and Sons Ltd., 2014) Garcia-Dorado, Ignacio; Aliaga, Daniel G.; Ukkusuri, Satish V.; B. Levy and J. KautzDesigning and optimizing traffic behavior and animation is a challenging problem of interest to virtual environment content generation and to urban planning and design. While some traffic simulation methods have appeared in computer graphics, most related systems focus on the design of buildings, roads, or cities but without explicitly considering urban traffic. To our knowledge, our work provides the first interactive approach which enables a designer to specify a desired vehicular traffic behavior (e.g., road occupancy, travel time, emissions, etc.) and the system will automatically compute what realistic 3D urban model (e.g., an interconnected network of roads, parcels, and buildings) yields the specified behavior. Our system both altered and improved traffic behavior in novel procedurally-generated cities and in road networks of existing cities. Our urban models contain up to 360 km of roads, 300,000 vehicles, and typically cover four hours of simulated peak traffic time. The typical editing session time to "paint" a new traffic pattern and to compute the new/changed urban model is two to five minutes.Item Pathline Glyphs(The Eurographics Association and John Wiley and Sons Ltd., 2014) Hlawatsch, Marcel; Sadlo, Filip; Jang, Hajun; Weiskopf, Daniel; B. Levy and J. KautzVisualization of pathlines is common and highly relevant for the analysis of unsteady flow. However, pathlines can intersect, leading to visual clutter and perceptual issues. This makes it intrinsically difficult to provide expressive visualizations of the entire domain by an arrangement of multiple pathlines, in contrast to well-established streamline placement techniques. We present an approach to reduce these problems. It is inspired by glyph-based visualization and small multiples: we partition the domain into cells, each corresponding to a downscaled version of the entire domain. Inside these cells, a single downscaled pathline is drawn. On the overview scale, our pathline glyphs lead to emergent visual patterns that provide insight into time-dependent flow behavior. Zooming-in allows us to analyze individual pathlines in detail and compare neighboring lines. The overall approach is complemented with a context-preserving zoom lens and interactive pathline-based exploration. While we primarily target the visualization of 2D flow, we also address the extension to 3D. Our evaluation includes several examples, comparison to other flow visualization techniques, and a user study with domain experts.Item SAFE: Structure-aware Facade Editing(The Eurographics Association and John Wiley and Sons Ltd., 2014) Dang, Minh; Ceylan, Duygu; Neubert, Boris; Pauly, Mark; B. Levy and J. KautzMany man-made objects, in particular building facades, exhibit dominant structural relations such as symmetry and regularity. When editing these shapes, a common objective is to preserve these relations. However, often there are numerous plausible editing results that all preserve the desired structural relations of the input, creating ambiguity. We propose an interactive facade editing framework that explores this structural ambiguity. We first analyze the input in a semi-automatic manner to detect different groupings of the facade elements and the relations among them. We then provide an incremental editing process where a set of variations that preserve the detected relations in a particular grouping are generated at each step. Starting from one input example, our system can quickly generate various facade configurationsItem A Randomized Algorithm for Natural Object Colorization(The Eurographics Association and John Wiley and Sons Ltd., 2014) Jin, Sou-Young; Choi, Ho Jin; Tai, Yu-Wing; B. Levy and J. KautzNatural objects often contain vivid color distribution with wide variety of colors. Conventional colorization techniques, on the other hand, produce colors that are relatively flat with little color variation. In this paper, we introduce a randomized algorithm which considers not only the value of target color but also the distribution of target color. In essence, our algorithm paints a color distribution to a region which synthesizes color distribution of a natural object. Our approach models the correlation between intensity and color in HSV color space in terms of H - S, H - V and S - V joint histogram. During the colorization process, we randomly swap and reassign color of a pixel to minimize a cost function that measures color consistency to its neighborhood and intensity-to-color correlation captured in the joint histogram. We tested our algorithm extensively on many natural objects and our user study confirms that our results are more vivid and natural compared to results from previous techniques.Item Analogy-Driven 3D Style Transfer(The Eurographics Association and John Wiley and Sons Ltd., 2014) Ma, Chongyang; Huang, Haibin; Sheffer, Alla; Kalogerakis, Evangelos; Wang, Rui; B. Levy and J. KautzStyle transfer aims to apply the style of an exemplar model to a target one, while retaining the target s structure. The main challenge in this process is to algorithmically distinguish style from structure, a high-level, potentially ill-posed cognitive task. Inspired by cognitive science research we recast style transfer in terms of shape analogies. In IQ testing, shape analogy queries present the subject with three shapes: source, target and exemplar, and ask them to select an output such that the transformation, or analogy, from the exemplar to the output is similar to that from the source to the target. The logical process involved in identifying the source-to-target analogies implicitly detects the structural differences between the source and target and can be used effectively to facilitate style transfer. Since the exemplar has a similar structure to the source, applying the analogy to the exemplar will provide the output we seek. The main technical challenge we address is to compute the source to target analogies, consistent with human logic. We observe that the typical analogies we look for consist of a small set of simple transformations, which when applied to the exemplar generate a continuous, seamless output model. To assemble a shape analogy, we compute an optimal set of source-to-target transformations, such that the assembled analogy best fits these criteria. The assembled analogy is then applied to the exemplar shape to produce the desired output model. We use the proposed framework to seamlessly transfer a variety of style properties between 2D and 3D objects and demonstrate significant improvements over the state of the art in style transfer. We further show that our framework can be used to successfully complete partial scans with the help of a user provided structural template, coherently propagating scan style across the completed surfaces.Item 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. KautzSynthesizing 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.Item 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. KautzMost 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.Item Clean Color: Improving Multi-filament 3D Prints(The Eurographics Association and John Wiley and Sons Ltd., 2014) Hergel, Jean; Lefebvre, Sylvain; B. Levy and J. KautzFused Filament Fabrication is an additive manufacturing process by which a 3D object is created from plastic filament. The filament is pushed through a hot nozzle where it melts. The nozzle deposits plastic layer after layer to create the final object. This process has been popularized by the RepRap community. Several printers feature multiple extruders, allowing objects to be formed from multiple materials or colors. The extruders are mounted side by side on the printer carriage. However, the print quality suffers when objects with color patterns are printed a disappointment for designers interested in 3D printing their colored digital models. The most severe issue is the oozing of plastic from the idle extruders: Plastics of different colors bleed onto each other giving the surface a smudged aspect, excess strings oozing from the extruder deposit on the surface, and holes appear due to this missing plastic. Fixing this issue is difficult: increasing the printing speed reduces oozing but also degrades surface quality on large prints the required speed level become impractical. Adding a physical mechanism increases cost and print time as extruders travel to a cleaning station. Instead, we rely on software and exploit degrees of freedom of the printing process. We introduce three techniques that complement each other in improving the print quality significantly. We first reduce the impact of oozing plastic by choosing a better azimuth angle for the printed part. We build a disposable rampart in close proximity of the part, giving the extruders the opportunity to wipe oozing strings and refill with hot plastic. We finally introduce a toolpath planner avoiding and hiding most of the defects due to oozing, and seamlessly integrating the rampart. We demonstrate our technique on several challenging multiple color prints, and show that our tool path planner improves the surface finish of single color prints as well.Item Manipulating Refractive and Reflective Binocular Disparity(The Eurographics Association and John Wiley and Sons Ltd., 2014) Dabala, Lukasz; Kellnhofer, Petr; Ritschel, Tobias; Didyk, Piotr; Templin, Krzysztof; Myszkowski, Karol; Rokita, P.; Seidel, Hans-Peter; B. Levy and J. KautzPresenting stereoscopic content on 3D displays is a challenging task, usually requiring manual adjustments. A number of techniques have been developed to aid this process, but they account for binocular disparity of surfaces that are diffuse and opaque only. However, combinations of transparent as well as specular materials are common in the real and virtual worlds, and pose a significant problem. For example, excessive disparities can be created which cannot be fused by the observer. Also, multiple stereo interpretations become possible, e. g., for glass, that both reflects and refracts, which may confuse the observer and result in poor 3D experience. In this work, we propose an efficient method for analyzing and controlling disparities in computer-generated images of such scenes where surface positions and a layer decomposition are available. Instead of assuming a single per-pixel disparity value, we estimate all possibly perceived disparities at each image location. Based on this representation, we define an optimization to find the best per-pixel camera parameters, assuring that all disparities can be easily fused by a human. A preliminary perceptual study indicates, that our approach combines comfortable viewing with realistic depiction of typical specular scenes.Item Automatic Generation of Tourist Brochures(The Eurographics Association and John Wiley and Sons Ltd., 2014) Birsak, Michael; Musialski, Przemyslaw; Wonka, Peter; Wimmer, Michael; B. Levy and J. KautzWe present a novel framework for the automatic generation of tourist brochures that include routing instructions and additional information presented in the form of so-called detail lenses. The first contribution of this paper is the automatic creation of layouts for the brochures. Our approach is based on the minimization of an energy function that combines multiple goals: positioning of the lenses as close as possible to the corresponding region shown in an overview map, keeping the number of lenses low, and an efficient numbering of the lenses. The second contribution is a route-aware simplification of the graph of streets used for traveling between the points of interest (POIs). This is done by reducing the graph consisting of all shortest paths through the minimization of an energy function. The output is a subset of street segments that enable traveling between all the POIs without considerable detours, while at the same time guaranteeing a clutter-free visualization.Item Crack-free Rendering of Dynamically Tesselated B-Rep Models(The Eurographics Association and John Wiley and Sons Ltd., 2014) Claux, Frédéric; Barthe, Loïc; Vanderhaeghe, David; Jessel, Jean-Pierre; Paulin, Mathias; B. Levy and J. KautzWe propose a versatile pipeline to render B-Rep models interactively, precisely and without rendering-related artifacts such as cracks. Our rendering method is based on dynamic surface evaluation using both tesselation and ray-casting, and direct GPU surface trimming. An initial rendering of the scene is performed using dynamic tesselation. The algorithm we propose reliably detects then fills up cracks in the rendered image. Crack detection works in image space, using depth information, while crack-filling is either achieved in image space using a simple classification process, or performed in object space through selective ray-casting. The crack filling method can be dynamically changed at runtime. Our image space crack filling approach has a limited runtime cost and enables high quality, real-time navigation. Our higher quality, object space approach results in a rendering of similar quality than full-scene ray-casting, but is 2 to 6 times faster, can be used during navigation and provides accurate, reliable rendering. Integration of our work with existing tesselation-based rendering engines is straightforward.Item Light Montage for Perceptual Image Enhancement(The Eurographics Association and John Wiley and Sons Ltd., 2014) Hosu, Vlad; Ha, Mai Lan; Sim, Terence; B. Levy and J. KautzRecent photography techniques such as sculpting with light show great potential in compositing beautiful images from fixed-viewpoint photos under multiple illuminations. The process relies heavily on the artists experience and skills using the available tools. An apparent trend in recent works is to facilitate the interaction making it less timeconsuming and addressable not only to experts, but also novices. We propose a method that automatically creates enhanced light montages that are comparable to those produced by artists. It detects and emphasizes cues that are important for perception by introducing a technique to extract depth and shape edges from an unconstrained light stack. Studies show that these cues are associated with silhouettes and suggestive contours which artists use to sketch and construct the layout of paintings. Textures, due to perspective distortion, offer essential cues that depict shape and surface slant. We balance the emphasis between depth edges and reflectance textures to enhance the sense of both shape and reflectance properties. Our light montage technique works perfectly with a few to hundreds of illuminations for each scene. Experiments show great results for static scenes making it practical for small objects, interiors and small-scale outdoor scenes. Dynamic scenes may be captured using spatially distributed light setups such as light domes. The approach could also be applied to time-lapse photos, with the sun as the main light source.Item Recurring Part Arrangements in Shape Collections(The Eurographics Association and John Wiley and Sons Ltd., 2014) Zheng, Youyi; Cohen-Or, Daniel; Averkiou, Melinos; Mitra, Niloy J.; B. Levy and J. KautzExtracting semantically related parts across models remains challenging, especially without supervision. The common approach is to co-analyze a model collection, while assuming the existence of descriptive geometric features that can directly identify related parts. In the presence of large shape variations, common geometric features, however, are no longer sufficiently descriptive. In this paper, we explore an indirect top-down approach, where instead of part geometry, part arrangements extracted from each model are compared. The key observation is that while a direct comparison of part geometry can be ambiguous, part arrangements, being higher level structures, remain consistent, and hence can be used to discover latent commonalities among semantically related shapes. We show that our indirect analysis leads to the detection of recurring arrangements of parts, which are otherwise difficult to discover in a direct unsupervised setting. We evaluate our algorithm on ground truth datasets and report advantages over geometric similarity-based bottom-up co-segmentation algorithms.Item Compressing Dynamic Meshes with Geometric Laplacians(The Eurographics Association and John Wiley and Sons Ltd., 2014) Vasa, Libor; Marras, Stefano; Hormann, Kai; Brunnett, Guido; B. Levy and J. KautzThis paper addresses the problem of representing dynamic 3D meshes in a compact way, so that they can be stored and transmitted efficiently. We focus on sequences of triangle meshes with shared connectivity, avoiding the necessity of having a skinning structure. Our method first computes an average mesh of the whole sequence in edge shape space. A discrete geometric Laplacian of this average surface is then used to encode the coefficients that describe the trajectories of the mesh vertices. Optionally, a novel spatio-temporal predictor may be applied to the trajectories to further improve the compression rate. We demonstrate that our approach outperforms the current state of the art in terms of low data rate at a given perceived distortion, as measured by the STED and KG error metrics.Item 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. KautzIn 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.Item Rate-distortion Optimized Compression of Motion Capture Data(The Eurographics Association and John Wiley and Sons Ltd., 2014) Vasa, Libor; Brunnett, Guido; B. Levy and J. KautzLossy compression of motion capture data can alleviate the problems of efficient storage and transmission by exploiting the redundancy and the superfluous precision of the data. When considering the acceptable amount of distortion, perceptual issues have to be taken into account. Current state of the art methods reduce the data rate required for high quality storage of motion capture data using various techniques. Most of them, however, do not use the common tools of general data compression, such as the method of Lagrange multipliers, and thus they obtain sub-optimal results, making it difficult to do a fair comparison of their performance. In this paper, we present a general preprocessing step based on Lagrange multipliers, which allows to rigorously adjust the precision in each of the degrees of freedom of the input data according to the amount of influence the given degree of freedom has on the overall distortion. We then present a simple compression method based on Principal Component Analysis, which in combination with the proposed preprocessing achieves significantly better results than current state of the art methods. It allows optimization with respect to various distortion metrics, and we discuss the choice of the metric in two common but distinct scenarios, proposing a perceptually oriented comparison metric based on the relation of the problem at hand to the problem of compression of dynamic meshes.Item 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. KautzProcedural 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.Item Interactive Cloth Rendering of Microcylinder Appearance Model under Environment Lighting(The Eurographics Association and John Wiley and Sons Ltd., 2014) Iwasaki, Kei; Mizutani, Kazutaka; Dobashi, Yoshinori; Nishita, Tomoyuki; B. Levy and J. KautzThis paper proposes an interactive rendering method of cloth fabrics under environment lighting. The outgoing radiance from cloth fabrics in the microcylinder model is calculated by integrating the product of the distant environment lighting, the visibility function, the weighting function that includes shadowing/masking effects of threads, and the light scattering function of threads. The radiance calculation at each shading point of the cloth fabrics is simplified to a linear combination of triple product integrals of two circular Gaussians and the visibility function, multiplied by precomputed spherical Gaussian convolutions of the weighting function. We propose an efficient calculation method of the triple product of two circular Gaussians and the visibility function by using the gradient of signed distance function to the visibility boundary where the binary visibility changes in the angular domain of the hemisphere. Our GPU implementation enables interactive rendering of static cloth fabrics with dynamic viewpoints and lighting. In addition, interactive editing of parameters for the scattering function (e.g. thread s albedo) that controls the visual appearances of cloth fabrics can be achieved.