Short Papers
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Item Hybrid CPU/GPU KD-Tree Construction for Versatile Ray Tracing(The Eurographics Association, 2012) Roccia, Jean-Patrick; Paulin, Mathias; Coustet, Christophe; Carlos Andujar and Enrico PuppoWe propose an hybrid CPU-GPU ray-tracing implementation based on an optimal Kd-Tree as acceleration structure. The construction and traversal of this KD-tree takes benefit from both the CPU and the GPU to achieve high-performance ray-tracing on mainstream hardware. Our approach, flexible enough to use only a single computing unit (CPU or GPU), is able to efficiently distribute workload between CPUs and GPUs for fast KD-tree construction and traversal.Item Fast Response and Quick Progressive Transitions using Body Part Motion Graphs(The Eurographics Association, 2012) Fernández-Baena, Adso; Miralles, David; Carlos Andujar and Enrico PuppoInteractive applications where 3D character animation plays an important role need avatars ready to perform different activities. This objective has been accomplished in different works [LCR*02] [ZS09] that look for transition points in motion capture clips to allow transitions between them. These works ensure realism and smoothness but their responses and transition durations depend on transition points. Working with partial motions, such as body part motions, allows finding specific transition points for each part in order to optimize whole body transitions in a progressive way. This can be achieved with body part motion graphs (BPMG’s) [FBM11]. In this work we want to show that progressive transitions generated by BPMG’s have fast response and quick execution. In order to demonstrate this we have compared BPMG’s transitions against standard motion graphs (SMG) transitions. The results we have obtained show that our method allows more reaction velocity and execution. Moreover BPMG’s transitions are smoother than SMG transitions.Item Skeleton Based Importance Sampling for Path Tracing(The Eurographics Association, 2012) Biri, Venceslas; Chaussard, John; Carlos Andujar and Enrico PuppoWhen working with large and complex scenes, situations arise where light flux takes complex paths to reach the observer. In such cases, traditional stochastic algorithms, like ray tracing algorithms, will have difficulties to compute noise-free images. Our present research aims to solve this problem using the 3d scene skeleton as a coarse representation. Indeed, curvilinear skeletons can be used to find light paths with higher energy. This article presents our research to use these skeletons for any ray tracing algorithm, allowing a knowledge-based choice when choosing light paths. Our method adds little computation time while producing a more accurate image.Item Real-Time Metaball Ray Casting with Fragment Lists(The Eurographics Association, 2012) Szécsi, László; Illés, Dávid; Carlos Andujar and Enrico PuppoIn this paper we describe a method for rendering particle-based medium representations. The algorithm builds per-pixel lists of relevant metaballs, then incrementally constructs a piecewise polynomial approximation of summed metaball densities along rays, and finds intersections with the isosurface using those. This new approach scales well for a high number of particles, it can handle local extremities of depth complexity robustly, and it does not suffer from the inaccuracies and limitations of screen-space filtering approximation methods.Item Physically-Based Depth of Field in Augmented Reality(The Eurographics Association, 2012) Kán, Peter; Kaufmann, Hannes; Carlos Andujar and Enrico PuppoWe present a novel method for rendering and compositing video in augmented reality. We focus on calculating the physically correct result of the depth of field caused by a lens with finite sized aperture. In order to correctly simulate light transport, ray-tracing is used and in a single pass combined with differential rendering to compose the final augmented video. The image is fully rendered on GPUs, therefore an augmented video can be produced at interactive frame rates in high quality. Our method runs on the fly, no video postprocessing is needed. In addition we evaluated the user experiences with our rendering system with the hypothesis that a depth of field effect in augmented reality increases the realistic look of composited video. Results with 30 users show that 90% perceive videos with a depth of field considerably more realistic.Item Image-based Animation of Clothes(The Eurographics Association, 2012) Hilsmann, Anna; Eisert, Peter; Carlos Andujar and Enrico PuppoWe propose a pose-dependent image-based rendering approach for the visualization of clothes with very high rendering quality. Our representation combines body-pose-dependent geometry and appearance. A geometric model accounts for low-resolution shape adaptation, e.g. animation and view interpolation, while small details as well as complex shading/reflection properties are accounted for through numerous images. Information on shading, texture distortion and silhouette at fine wrinkles are extracted from the images to allow later texture replacement. The image-based representations are estimated in advance from real samples of clothes captured in an offline process, thus shifting computational complexity into the training phase. For rendering, pose dependent geometry and appearance are interpolated and merged from the stored representations.Item Improved Obstacle Relevancy, Distance, and Angle for Crowds Constrained to Arbitrary Manifolds in 3D Space(The Eurographics Association, 2012) Ricks, Brian C.; Egbert, Parris K.; Carlos Andujar and Enrico PuppoRecent work has proposed crowd simulation algorithms on arbitrary manifolds in 3D space. These algorithms simulate crowds on far more realistic surfaces than previously possible, including multi-story structures, science fiction scenarios, and habitats for insects and other animals that can walk on walls. However, current implementations can have distinct artifacts, including collision false positives and false negatives. Also, current implementations fail to account for the cylindrical shape of the characters being simulated. The resulting crowds move unnaturally and have obvious collisions. After identifying the cause of these artifacts, we propose an algorithm that does not struggle from these false positives or false negatives and correctly accounts for the non-spherical shape of agents. The resulting crowds move on large surfaces (over 100k triangles) running with a thousand agents in real-time.Item Growing Cell Structures Learning a Progressive Mesh During Surface Reconstruction - A Top-Down Approach(The Eurographics Association, 2012) Vierjahn, Tom; Lorenz, Guido; Mostafawy, Sina; Hinrichs, Klaus; Carlos Andujar and Enrico PuppoGrowing Cell Structures (GCS) have been proven to be suitable for surface reconstruction from unstructured point clouds. The reconstructed triangle mesh can be represented compactly as a progressive mesh with integrated level of detail by storing only vertex split operations. However, half-edge collapse operations are used for GCS. In this paper, we present an improvement to a GCS-based surface reconstruction technique by converting a halfedge collapse to a more general vertex removal to create a progressive mesh. We have evaluated the new technique with respect to running time overhead and mesh quality. Results indicate that this technique can be used for efficient surface reconstruction. We will use the presented findings as basis for future research.Item Hyperplane Culling for Stochastic Rasterization(The Eurographics Association, 2012) Munkberg, Jacob; Akenine-Möller, Tomas; Carlos Andujar and Enrico PuppoWe present two novel culling tests for rasterization of simultaneous depth of field and motion blur. These tests efficiently reduce the set of xyuvt samples that need to be coverage tested within a screen space tile. The first test finds linear bounds in ut- and vt-space using a separating line algorithm. We also derive a hyperplane in xyuvtspace for each triangle edge, and all samples outside of these planes are culled in our second test. Based on these tests, we present an efficient stochastic rasterizer, which has substantially higher sample test efficiency and lower arithmetic cost than previous tile-based stochastic rasterizers.Item Forward+: Bringing Deferred Lighting to the Next Level(The Eurographics Association, 2012) Harada, Takahiro; McKee, Jay; Yang, Jason C.; Carlos Andujar and Enrico PuppoThis paper presents Forward+, a method of rendering many lights by culling and storing only lights that contribute to the pixel. Forward+ is an extension to traditional forward rendering. Light culling, implemented using the compute capability of the GPU, is added to the pipeline to create lists of lights; that list is passed to the final rendering shader, which can access all information about the lights. Although Forward+ increases workload to the final shader, it theoretically requires less memory traffic compared to compute-based deferred lighting. Furthermore, it removes the major drawback of deferred techniques, which is a restriction of materials and lighting models. Experiments are performed to compare the performance of Forward+ and deferred lighting.Item Shape Reconstruction from Raw Point Clouds using Depth Carving(The Eurographics Association, 2012) Guggeri, Fabio; Scateni, Riccardo; Pajarola, Renato; Carlos Andujar and Enrico PuppoShape reconstruction from raw point sets is a hot research topic. Point sets are increasingly available as primary input source, since low-cost acquisition methods are largely accessible nowadays, and these sets are more noisy than used to be. Standard reconstruction methods rely on normals or signed distance functions, and thus many methods aim at estimating these features. Human vision can however easily discern between the inside and the outside of a dense cloud even without the support of fancy measures. We propose, here, a perceptual method for estimating an indicator function for the shape, inspired from image-based methods. The resulting function nicely approximates the shape, is robust to noise, and can be used for direct isosurface extraction or as an input for other accurate reconstruction methods.Item Perceptually Based Afterimage Synthesis(The Eurographics Association, 2012) Mikamo, Michihiro; Slomp, Marcos; Raytchev, Bisser; Tamaki, Toru; Kaneda, Kazufumi; Carlos Andujar and Enrico PuppoAfterimages comprise a common, recurring perceptual phenomenon experienced in a daily-basis. Afterimages are best realized when staring at some high intensity light source (i.e., a light bulb) and then shifting the ocular focus to other less luminous portions of the scene: a temporary “ghost” image of that strong intensity remains imprinted on the retina. During the time the afterimage stays active, several exquisite color gradations appear and fade. Although research on the topic has been moderately active in ophthalmology and vision domains, no definitive model has been devised. Furthermore, no afterimage simulation seems to have yet been investigated in computer graphics. In this paper we attempt to introduce the topic to the field and therefore widen the research spectrum of computer graphics. The proposed technique is based on psychophysical and physiological evidence, addressing the color transitions and the duration of the effect. The method is also fast and suitable for real-time applications. Our stance towards afterimages is more than just curiosity on this peculiar effect: we believe that its understanding and proper simulation can assist on relevant tasks such as urban and road engineering for safer pedestrian and vehicle mobility at adverse lighting conditions.Item Automatic Multi-view Surface Matching(The Eurographics Association, 2012) Fantoni, Simone; Castellani, Umberto; Fusiello, Andrea; Carlos Andujar and Enrico PuppoIn this paper we tackle the problem of automatically aligning an unordered set of range views. We propose a full pipeline that goes from the scans to the complete 3D model. The emphasis is on the automation no manual intervention is require and on the fact that no knowledge on the acquisition sequence is assumed. The contribution is twofold: in the pre-alignment phase a voting scheme is proposed that discovers the overlapping relationship among views; in the final refinement step we extend the Levenberg Marquardt-ICP to work with multiple views, in order to solve for the absolute pose of all images simultaneously.Item Variation-Factored Encoding of Facade Images(The Eurographics Association, 2012) Alsisan, Suhib; Mitra, Niloy J.; Carlos Andujar and Enrico PuppoUrban facades contain large-scale repetitions in the form of windows, doors, etc. Such elements often are in different configurations (e.g., open or closed) obscuring their regular arrangements to any direct low-level pixel matching based repetition detection.We propose a variation-factored representation for facade images by progressively favoring larger repeated structures while allowing relabeling using candidate element types. We formulate the problem as a Markov Random Field (MRF) based optimization, and evaluate the algorithm on a large number of benchmark facade images. Such a facade encoding is very compact and can be used for rapid generation of realistic 3D models with variations suitable for online map viewers or mobile navigation aids.Item Scented Sliders for Procedural Textures(The Eurographics Association, 2012) Lasram, Anass; Lefebvre, Sylvain; Damez, Cyrille; Carlos Andujar and Enrico PuppoProcedural textures often expose a set of parameters controlling their final appearance. This lets end users tune the final look and feel, typically through a set of sliders. However, it is difficult to predict the changes introduced by a given slider, especially as sliders interact in non–trivial ways. We augment the sliders controlling parameters with visual previews revealing the changes that will be introduced upon manipulation. These previews are constantly refreshed to reflect changes with respect to the current settings. The main challenge is to generate the visual sliders in a very limited pixel space and at an interactive rate. This is done by synthesizing the visual slider from a small set of patches ordered in accordance with the slider. These patches are chosen so as to reveal as much as possible the visual variations induced by the slider. The selection and ordering are achieved by using the seam–carving algorithm to carve patches with low visual impact. The obtained patches are then stitched together using patch-based texture synthesis to form the final visual slider.Item FTLE Computation Beyond First-Order Approximation(The Eurographics Association, 2012) Üffinger, Markus; Sadlo, Filip; Kirby, Mike; Hansen, Charles; Ertl, Thomas; Carlos Andujar and Enrico PuppoWe present a framework for different approaches to finite-time Lyapunov exponent (FTLE) computation for 2D vector fields, based on the advection of seeding circles. On the one hand it unifies the popular flow map approach with techniques based on the evaluation of distinguished trajectories, such as renormalization. On the other hand it allows for the exploration of their order of approximation (first-order approximation representing the flow map gradient). Using this framework, we derive a measure for nonlinearity of the flow map, that brings us to the definition of a new FTLE approach. We also show how the nonlinearity measure can be used as a criterion for flow map refinement for more accurate FTLE computation, and we demonstrate that ridge extraction in supersampled FTLE leads to superior ridge quality.Item Automatic Line Handles for Freeform Deformation(The Eurographics Association, 2012) Schemali, Leïla; Thiery, Jean-Marc; Boubekeur, Tamy; Carlos Andujar and Enrico PuppoInteractive freeform surface deformation methods allow to explore the space of possible shapes using simple control structures. While recent advances in variational editing provide high quality deformations, designing control structures remains a time-consuming manual process. We propose a new automatic control structure generation based on the observation that the most salient visual structures of a surface, such as the one exploited in Line Drawing methods, are tightly linked to the potential deformations it may undergo. Our basic idea is to build control structures from those lines in order to provide users with an automatic set of deformation handles to grab and manipulate, avoiding the tedious task of region selection and handle positioning. The resulting interface inherits view-dependency and adaptivity from line definitions, reduces significantly the modeling session time in a number of scenarii, and remains fully compatible with classical handle-based deformations.Item Incoherent Ray Tracing without Acceleration Structures(The Eurographics Association, 2012) Áfra, Attila T.; Carlos Andujar and Enrico PuppoRecently, a new family of dynamic ray tracing algorithms, called divide-and-conquer ray tracing, has been introduced. This approach partitions the primitives on-the-fly during ray traversal, which eliminates the need for an acceleration structure. We present a new ray traversal method based on this principle, which efficiently handles incoherent rays, and takes advantage of the SSE and AVX instruction sets of the CPU. Our algorithm offers notable performance improvements over similar existing solutions, and it is competitive with powerful static ray tracers.Item Efficient Evaluation of Semi-Smooth Creases in Catmull-Clark Subdivision Surfaces(The Eurographics Association, 2012) Nießner, Matthias; Loop, Charles; Greiner, Günther; Carlos Andujar and Enrico PuppoWe present a novel method to evaluate semi-smooth creases in Catmull-Clark subdivision surfaces. Our algorithm supports both integer and fractional crease tags corresponding to the RenderMan (Pixar) specification. In order to perform fast and efficient surface evaluations, we obtain a polynomial surface representation given by the semismooth subdivision rules. While direct surface evaluation is applied for regular patches, we perform adaptive subdivision around extraordinary vertices. In the end, we are able to efficently handle high-order sharpness tags at very low cost. Compared to the state-of-the art, both render time and memory consumption are reduced from exponential to linear complexity. Furthermore, we integrate our algorithm in the hardware tessellation pipeline of modern GPUs. Our method is ideally suited to real-time applications such as games or authoring tools.Item Geometric Details on Skeleton-based Implicit Surfaces(The Eurographics Association, 2012) Zanni, Cedric; Bares, P.; Lagae, Ares; Quiblier, M.; Cani, Marie-Paule; Carlos Andujar and Enrico PuppoWe present a modeling technique to enhance implicit surfaces with procedural geometric details. The details are based on Gabor noise, which enables us to seamlessly handle anisotropy. The orientation of details can be defined with respect to the orientation of the main shape features, which reduces the amount of user input. The method extends to complex details that are tilted with respect to the normal of the input surface. Lastly, our method allows the blending of the resulting enhanced implicit primitives without causing the details to blur.