32-Issue 2
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Item Rendering Gigaray Light Fields(The Eurographics Association and Blackwell Publishing Ltd., 2013) Birklbauer, Clemens; Opelt, Simon; Bimber, Oliver; I. Navazo, P. PoulinWe present a caching framework with a novel probability-based prefetching and eviction strategy applied to atomic cache units that enables interactive rendering of gigaray light fields. Further, we describe two new use cases that are supported by our framework: panoramic light fields, including a robust imaging technique and an appropriate parameterization scheme for real-time rendering and caching; and light-field-cached volume rendering, which supports interactive exploration of large volumetric datasets using light-field rendering. We consider applications such as light-field photography and the visualization of large image stacks from modern scanning microscopes.Item Capturing Relightable Human Performances under General Uncontrolled Illumination(The Eurographics Association and Blackwell Publishing Ltd., 2013) Li, Guannan; Wu, Chenglei; Stoll, Carsten; Liu, Yebin; Varanasi, Kiran; Dai, Qionghai; Theobalt, Christian; I. Navazo, P. PoulinWe present a novel approach to create relightable free-viewpoint human performances from multi-view video recorded under general uncontrolled and uncalibated illumination.We first capture a multi-view sequence of an actor wearing arbitrary apparel and reconstruct a spatio-temporal coherent coarse 3D model of the performance using a marker-less tracking approach. Using these coarse reconstructions, we estimate the low-frequency component of the illumination in a spherical harmonics (SH) basis as well as the diffuse reflectance, and then utilize them to estimate the dynamic geometry detail of human actors based on shading cues. Given the high-quality time-varying geometry, the estimated illumination is extended to the all-frequency domain by re-estimating it in the wavelet basis. Finally, the high-quality all-frequency illumination is utilized to reconstruct the spatially-varying BRDF of the surface. The recovered time-varying surface geometry and spatially-varying non-Lambertian reflectance allow us to generate high-quality model-based free view-point videos of the actor under novel illumination conditions. Our method enables plausible reconstruction of relightable dynamic scene models without a complex controlled lighting apparatus, and opens up a path towards relightable performance capture in less constrained environments and using less complex acquisition setups.Item Pose Space Image Based Rendering(The Eurographics Association and Blackwell Publishing Ltd., 2013) Hilsmann, Anna; Fechteler, Philipp; Eisert, Peter; I. Navazo, P. PoulinThis paper introduces a new image-based rendering approach for articulated objects with complex pose-dependent appearance, such as clothes. Our approach combines body-pose-dependent appearance and geometry to synthesize images of new poses from a database of examples. A geometric model allows animation and view interpolation, while small details as well as complex shading and reflection properties are modeled by pose-dependent appearance examples in a database. Correspondences between the images are represented as mesh-based warps, both in the spatial and intensity domain. For rendering, these warps are interpolated in pose space, i.e. the space of body poses, using scattered data interpolation methods. Warp estimation as well as geometry reconstruction is performed in an offline procedure, thus shifting computational complexity to an a-priori training phase.Item Sifted Disks(The Eurographics Association and Blackwell Publishing Ltd., 2013) Ebeida, Mohamed S.; Mahmoud, Ahmed H.; Awad, Muhammad A.; Mohammed, Mohammed A.; Mitchell, Scott A.; Rand, Alexander; Owens, John D.; I. Navazo, P. PoulinWe introduce the Sifted Disk technique for locally resampling a point cloud in order to reduce the number of points. Two neighboring points are removed and we attempt to find a single random point that is sufficient to replace them both. The resampling respects the original sizing function; In that sense it is not a coarsening. The angle and edge length guarantees of a Delaunay triangulation of the points are preserved. The sifted point cloud is still suitable for texture synthesis because the Fourier spectrum is largely unchanged. We provide an efficient algorithm, and demonstrate that sifting uniform Maximal Poisson-disk Sampling (MPS) and Delaunay Refinement (DR) points reduces the number of points by about 25 percent, and achieves a density about 1/3 more than the theoretical minimum. We show two-dimensional stippling and meshing applications to demonstrate the significance of the concept.Item Locally Adaptive Products for All-Frequency Relighting(The Eurographics Association and Blackwell Publishing Ltd., 2013) Inger, Yaron; Farbman, Zeev; Lischinski, Dani; I. Navazo, P. PoulinTriple product integrals evaluate the shading at a point by factoring the reflection equation into incident illumination, visibility, and BRDF. By densely sampling the space of incident directions, this approach is capable of highly accurate rendering scenes lit by high-frequency environment lighting, containing complex materials and featuring intricate shadows. Efficient evaluation of triple product integrals using Haar wavelets enables near-interactive rendering of such scenes, while dynamically changing the lighting and the view. Although faster methods have been proposed in the recent real-time rendering literature, the approximations employed in these methods typically limit them to lower frequency phenomena. In this paper, we present a new approach for high-frequency scene relighting within the triple product framework. Our approach breaks the computation to smaller solid angles (blocks) over most of which the triple product degenerates to a dot product. We introduce a lossless, yet compact, differential representation of the visibility function over each block, and sample the BRDF on the fly, eliminating the need to store multiple rotated copies of each BRDF. By combining these ideas, we are able to achieve true interactive performance even when running on a CPU, while supporting high frequency effects in scenes with high vertex counts.Item Path Space Regularization for Holistic and Robust Light Transport(The Eurographics Association and Blackwell Publishing Ltd., 2013) Kaplanyan, Anton S.; Dachsbacher, Carsten; I. Navazo, P. PoulinWe propose a simple yet powerful regularization framework for robust light transport simulation. It builds on top of existing unbiased methods and resorts to a consistent estimation using regularization only for paths which cannot be sampled in an unbiased way. To introduce as little bias as possible, we selectively regularize individual interactions along paths, and also derive the regularization consistency conditions. Our approach is compatible with the majority of unbiased methods, e.g. (bidirectional) path tracing and Metropolis light transport (MLT), and only a simple modification is required to adapt existing renderers. We compare to recent unbiased and consistent methods and show examples of scenes with difficult light paths, where regularization is required to account for all illumination features. When coupled with MLT we are able to sample all phenomena, like recent consistent methods, while achieving superior convergence.Item Gaze-driven Object Tracking for Real Time Rendering(The Eurographics Association and Blackwell Publishing Ltd., 2013) Mantiuk, Radoslaw; Bazyluk, Bartosz; Mantiuk, Rafal K.; I. Navazo, P. PoulinTo efficiently deploy eye-tracking within 3D graphics applications, we present a new probabilistic method that predicts the patterns of user's eye fixations in animated 3D scenes from noisy eye-tracker data. The proposed method utilises both the eye-tracker data and the known information about the 3D scene to improve the accuracy, robustness and stability. Eye-tracking can thus be used, for example, to induce focal cues via gaze-contingent depth-of-field rendering, add intuitive controls to a video game, and create a highly reliable scene-aware saliency model. The computed probabilities rely on the consistency of the gaze scan-paths to the position and velocity of a moving or stationary target. The temporal characteristic of eye fixations is imposed by a Hidden Markov model, which steers the solution towards the most probable fixation patterns. The derivation of the algorithm is driven by the data from two eye-tracking experiments: the first experiment provides actual eye-tracker readings and the position of the target to be tracked. The second experiment is used to derive a JND-scaled (Just Noticeable Difference) quality metric that quantifies the perceived loss of quality due to the errors of the tracking algorithm. Data from both experiments are used to justify design choices, and to calibrate and validate the tracking algorithms. This novel method outperforms commonly used fixation algorithms and is able to track objects smaller then the nominal error of an eye-tracker.Item A Correlated Parts Model for Object Detection in Large 3D Scans(The Eurographics Association and Blackwell Publishing Ltd., 2013) Sunkel, Martin; Jansen, Silke; Wand, Michael; Seidel, Hans-Peter; I. Navazo, P. PoulinThis paper addresses the problem of detecting objects in 3D scans according to object classes learned from sparse user annotation. We model objects belonging to a class by a set of fully correlated parts, encoding dependencies between local shapes of different parts as well as their relative spatial arrangement. For an efficient and comprehensive retrieval of instances belonging to a class of interest, we introduce a new approximate inference scheme and a corresponding planning procedure. We extend our technique to hierarchical composite structures, reducing training effort and modeling spatial relations between detected instances. We evaluate our method on a number of real-world 3D scans and demonstrate its benefits as well as the performance of the new inference algorithm.Item Landmark-Guided Elastic Shape Analysis of Spherically-Parameterized Surfaces(The Eurographics Association and Blackwell Publishing Ltd., 2013) Kurtek, Sebastian; Srivastava, Anuj; Klassen, Eric; Laga, Hamid; I. Navazo, P. PoulinWe argue that full surface correspondence (registration) and optimal deformations (geodesics) are two related problems and propose a framework that solves them simultaneously. We build on the Riemannian shape analysis of anatomical and star-shaped surfaces of Kurtek et al. and focus on articulated complex shapes that undergo elastic deformations and that may contain missing parts. Our core contribution is the re-formulation of Kurtek et al.'s approach as a constrained optimization over all possible re-parameterizations of the surfaces, using a sparse set of corresponding landmarks. We introduce a landmark-constrained basis, which we use to numerically solve this optimization and therefore establish full surface registration and geodesic deformation between two surfaces. The length of the geodesic provides a measure of dissimilarity between surfaces. The advantages of this approach are: (1) simultaneous computation of full correspondence and geodesic between two surfaces, given a sparse set of matching landmarks (2) ability to handle more comprehensive deformations than nearly isometric, and (3) the geodesics and the geodesic lengths can be further used for symmetrizing 3D shapes and for computing their statistical averages. We validate the framework on challenging cases of large isometric and elastic deformations, and on surfaces with missing parts. We also provide multiple examples of averaging and symmetrizing 3D models.Item Accurate Binary Image Selection from Inaccurate User Input(The Eurographics Association and Blackwell Publishing Ltd., 2013) Subr, Kartic; Paris, Sylvain; Soler, Cyril; Kautz, Jan; I. Navazo, P. PoulinSelections are central to image editing, e.g., they are the starting point of common operations such as copy-pasting and local edits. Creating them by hand is particularly tedious and scribble-based techniques have been introduced to assist the process. By interpolating a few strokes specified by users, these methods generate precise selections. However, most of the algorithms assume a 100 percent accurate input, and even small inaccuracies in the scribbles often degrade the selection quality, which imposes an additional burden on users. In this paper, we propose a selection technique tolerant to input inaccuracies. We use a dense conditional random field (CRF) to robustly infer a selection from possibly inaccurate input. Further, we show that patch-based pixel similarity functions yield more precise selection than simple point-wise metrics. However, efficiently solving a dense CRF is only possible in low-dimensional Euclidean spaces, and the metrics that we use are high-dimensional and often non-Euclidean.We address this challenge by embedding pixels in a low-dimensional Euclidean space with a metric that approximates the desired similarity function. The results show that our approach performs better than previous techniques and that two options are sufficient to cover a variety of images depending on whether the objects are textured.Item Global Selection of Stream Surfaces(The Eurographics Association and Blackwell Publishing Ltd., 2013) Esturo, Janick Martinez; Schulze, Maik; Rössl, Christian; Theisel, Holger; I. Navazo, P. PoulinStream surfaces are well-known and widely-used structures for 3D flow visualization. A single surface can be sufficient to represent important global flow characteristics. Unfortunately, due to the huge space of possible stream surfaces, finding the globally most representative stream surface turns out to be a hard task that is usually performed by time-consuming manual trial and error exploration using slight modifications of seed geometries. To assist users we propose a new stream surface selection method that acts as an automatic preprocessing step before data analysis. We measure stream surface relevance by a novel surface-based quality measure that prefers surfaces where the flow is aligned with principal curvature directions. The problem of seed structure selection can then be reduced to the computation of simple minimal paths in a weighted graph spanning the domain. We apply a simulated annealing-based optimization method to find smooth seed curves of globally near-optimal stream surfaces. We illustrate the effectiveness of our method on a series of synthetic and real-world data sets.Item Surface Reconstruction through Point Set Structuring(The Eurographics Association and Blackwell Publishing Ltd., 2013) Lafarge, Florent; Alliez, Pierre; I. Navazo, P. PoulinWe present a method for reconstructing surfaces from point sets. The main novelty lies in a structure-preserving approach where the input point set is first consolidated by structuring and resampling the planar components, before reconstructing the surface from both the consolidated components and the unstructured points. The final surface is obtained through solving a graph-cut problem formulated on the 3D Delaunay triangulation of the structured point set where the tetrahedra are labeled as inside or outside cells. Structuring facilitates the surface reconstruction as the point set is substantially reduced and the points are enriched with structural meaning related to adjacency between primitives. Our approach departs from the common dichotomy between smooth/piecewisesmooth and primitive-based representations by gracefully combining canonical parts from detected primitives and free-form parts of the inferred shape. Our experiments on a variety of inputs illustrate the potential of our approach in terms of robustness, flexibility and efficiency.Item Photon Parameterisation for Robust Relaxation Constraints(The Eurographics Association and Blackwell Publishing Ltd., 2013) Spencer, Ben; Jones, Mark W.; I. Navazo, P. PoulinThis paper presents a novel approach to detecting and preserving fine illumination structure within photon maps. Data derived from each photon's primal trajectory is encoded and used to build a high-dimensional kd-tree. Incorporation of these new parameters allows for precise differentiation between intersecting ray envelopes, thus minimizing detail degradation when combined with photon relaxation. We demonstrate how parameter-aware querying is beneficial in both detecting and removing noise. We also propose a more robust structure descriptor based on principal components analysis that better identifies anisotropic detail at the sub-kernel level.We illustrate the effectiveness of our approach in several example scenes and show significant improvements when rendering complex caustics compared to previous methods.Item Physics Storyboards(The Eurographics Association and Blackwell Publishing Ltd., 2013) Ha, Sehoon; McCann, Jim; Liu, C. Karen; Popovic, Jovan; I. Navazo, P. PoulinPhysical simulation and other procedural methods are increasingly popular tools in interactive applications because they generate complex and reactive behaviors given only a few parameter settings. This automation accelerates initial implementation, but also introduces a need to tune the available parameters until the desired behaviors emerge. These adjustments are typically performed iteratively, with the designer repeatedly running- and interacting with-the procedural animation with different parameter settings. Such a process is inaccurate, time consuming, and requires deep understanding and intuition, as parameters often have complex, nonlinear effects. Instead, we propose that designers construct physics storyboards to accelerate the process of tuning interactive, procedural animations. Physics storyboards are collections of space-time snapshots that highlight critical events and outcomes. They can be used to summarize the effects of parameter changes (without requiring the designer to perform extensive play-testing); and-when augmented with designer-provided evaluation functions-allow automatic parameter selection. We describe our implementation of this method, including how we use sampling to ensure that our automatically-selected parameters generalize, and how we time-warp user input to adapt it to changing parameters. We validate our implementation by using it to perform various design tasks in three example games.Item View-Dependent Realtime Rendering of Procedural Facades with High Geometric Detail(The Eurographics Association and Blackwell Publishing Ltd., 2013) Krecklau, Lars; Born, Janis; Kobbelt, Leif; I. Navazo, P. PoulinWe present an algorithm for realtime rendering of large-scale city models with procedurally generated facades. By using highly detailed assets like windows, doors, and decoration such city models can provide an extremely high geometric level of detail but on the downside they also consist of billions of polygons which makes it infeasible to even store them as explicit polygonal meshes. Moreover, when rendering urban scenes usually only a very small fraction of the city is actually visible which calls for effective culling mechanisms. For procedural textures there are efficient screen space techniques that evaluate, e.g., a split grammar on a per-pixel basis in the fragment shader and thus render a textured facade in a view dependent manner. We take this idea further by introducing 3D geometric detail in addition to flat textures. Our approach is a two-pass procedure that first renders a flat procedural facade. During rasterization the fragment shader triggers the instantiation of a detailed asset whenever a geometric facade element is potentially visible. The set of instantiated detail models are then rendered in a second pass. The major challenges arise from the fact that geometric details belonging to a facade can be visible even if the base polygon of the facade itself is not visible. Hence we propose measures to conservatively estimate visibility without introducing excessive redundancy. We further extend our technique by a simple level of detail mechanism that switches to baked textures (of the assets) depending on the distance to the camera. We demonstrate that our technique achieves realtime frame rates for large-scale city models with massive detail on current commodity graphics hardware.Item Geometry-Aware Volume-of-Fluid Method(The Eurographics Association and Blackwell Publishing Ltd., 2013) Cho, Junghyun; Ko, Hyeong-Seok; I. Navazo, P. PoulinWe present a new framework to simulate moving interfaces in viscous incompressible two phase flows. The goal is to achieve both conservation of the fluid volume and a detailed reconstruction of the fluid surface. To these ends, we incorporate sub-grid refinement of the level set with the volume-of-fluid method. In the context of this refined level set grid we propose the algorithms needed for the coupling of the level set and the volume-of-fluid, which include techniques for computing volume, redistancing the level set, and handling surface tension. We report the experimental results produced with the proposed method via simulations of the two phase fluid phenomena such as air-cushioning and deforming large bubbles.Item Stylized and Performative Gaze for Character Animation(The Eurographics Association and Blackwell Publishing Ltd., 2013) Pejsa, Tomislav; Mutlu, Bilge; Gleicher, Michael; I. Navazo, P. PoulinExisting models of gaze motion for character animation simulate human movements, incorporating anatomical, neurophysiological, and functional constraints. While these models enable the synthesis of humanlike gaze motion, they only do so in characters that conform to human anatomical proportions, causing undesirable artifacts such as cross-eyedness in characters with non-human or exaggerated human geometry. In this paper, we extend a state-of-the- art parametric model of human gaze motion with control parameters for specifying character geometry, gaze dynamics, and performative characteristics in order to create an enhanced model that supports gaze motion in characters with a wide range of geometric properties that is free of these artifacts. The model also affords ''staging effects'' by offering softer functional constraints and more control over the appearance of the character's gaze movements. An evaluation study showed that the model, compared with the state-of-the-art model, creates gaze motion with fewer artifacts in characters with non-human or exaggerated human geometry while retaining their naturalness and communicative accuracy.Item A Novel Projection Technique with Detail Capture and Shape Correction for Smoke Simulation(The Eurographics Association and Blackwell Publishing Ltd., 2013) Wu, Xiaoyue; Yang, Xubo; Yang, Yang; I. Navazo, P. PoulinSmoke simulation on a large grid is quite time consuming and most of the computation time is spent on the projection step.We present a novel projection method which produces quite similar visual results as those produced with the traditional projection method, but uses much less computation time. Our method includes two steps: detail-capture and shape-correction. The first step preserves most of the smoke details using an efficient DST (Discrete Sine Transformation) Poisson Solver with auxiliary boundary sweeping. The second step maintains the overall flow shape by solving a correcting Poisson equation on a coarse grid. Our algorithm is very fast and quite easy to implement. Experiments show that our projection is approximately 10-30 times faster than the traditional projection with PCG(Preconditioned Conjugate Gradient), while convincingly preserving both the flow details and the overall shape of the smoke.Item Coupled Quasi-harmonic Bases(The Eurographics Association and Blackwell Publishing Ltd., 2013) Kovnatsky, Artiom; Bronstein, Michael M.; Bronstein, Alexander M.; Glashoff, Klaus; Kimmel, Ron; I. Navazo, P. PoulinThe use of Laplacian eigenbases has been shown to be fruitful in many computer graphics applications. Today, state-of-the-art approaches to shape analysis, synthesis, and correspondence rely on these natural harmonic bases that allow using classical tools from harmonic analysis on manifolds. However, many applications involving multiple shapes are obstacled by the fact that Laplacian eigenbases computed independently on different shapes are often incompatible with each other. In this paper, we propose the construction of common approximate eigenbases for multiple shapes using approximate joint diagonalization algorithms, taking as input a set of corresponding functions (e.g. indicator functions of stable regions) on the two shapes. We illustrate the benefits of the proposed approach on tasks from shape editing, pose transfer, correspondence, and similarity.Item Stochastic Depth Buffer Compression using Generalized Plane Encoding(The Eurographics Association and Blackwell Publishing Ltd., 2013) Andersson, Magnus; Munkberg, Jacob; Akenine-Möller, Tomas; I. Navazo, P. PoulinIn this paper, we derive compact representations of the depth function for a triangle undergoing motion or defocus blur. Unlike a static primitive, where the depth function is planar, the depth function is a rational function in time and the lens parameters. Furthermore, we show how these compact depth functions can be used to design an efficient depth buffer compressor/decompressor, which significantly lowers total depth buffer bandwidth usage for a range of test scenes. In addition, our compressor/decompressor is simpler in the number of operations needed to execute, which makes our algorithm more amenable for hardware implementation than previous methods