Volume 28 (2009)

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Approximating Gradients for Meshes and Point Clouds via Diffusion Metric
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Luo, Chuanjiang; Safa, Issam; Wang, Yusu
The gradient of a function defined on a manifold is perhaps one of the most important differential objects in data analysis. Most often in practice, the input function is available only at discrete points sampled from the underlying manifold, and the manifold is approximated by either a mesh or simply a point cloud. While many methods exist for computing gradients of a function defined over a mesh, computing and simplifying gradients and related quantities such as critical points, of a function from a point cloud is non-trivial.In this paper, we initiate the investigation of computing gradients under a different metric on the manifold from the original natural metric induced from the ambient space. Specifically, we map the input manifold to the eigenspace spanned by its Laplacian eigenfunctions, and consider the so-called diffusion distance metric associated with it. We show the relation of gradient under this metric with that under the original metric. It turns out that once the Laplace operator is constructed, it is easier to approximate gradients in the eigenspace for discrete inputs (especially point clouds) and it is robust to noises in the input function and in the underlying manifold. More importantly, we can easily smooth the gradient field at different scales within this eigenspace framework. We demonstrate the use of our new eigen-gradients with two applications: approximating / simplifying the critical points of a function, and the Jacobi sets of two input functions (which describe the correlation between these two functions), from point clouds data.
Fast Four-Way Parallel Radix Sorting on GPUs
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Ha, Linh; Krueger, Jens; Silva, Claudio T.
Efficient sorting is a key requirement for many computer science algorithms. Acceleration of existing techniques as well as developing new sorting approaches is crucial for many real-time graphics scenarios, database systems, and numerical simulations to name just a few. It is one of the most fundamental operations to organize and filter the ever growing massive amounts of data gathered on a daily basis. While optimal sorting models for serial execution on a single processor exist, efficient parallel sorting remains a challenge. In this paper, we present a hardware-optimized parallel implementation of the radix sort algorithm that results in a significant speed up over existing sorting implementations. We outperform all known General Processing Unit (GPU) based sorting systems by about a factor of two and eliminate restrictions on the sorting key space. This makes our algorithm not only the fastest, but also the first general GPU sorting solution.
Adaptive Interleaved Sampling for Interactive High-Fidelity Rendering
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Dubla, P.; Debattista, K.; Chalmers, A.
Recent advances have made interactive ray tracing (IRT) possible on consumer desktop machines. These advances have brought about the potential for interactive global illumination (IGI) with enhanced realism through physically based lighting. IGI, unlike IRT, has a much higher computational complexity. Furthermore, since non-primary rays constitute the majority of the computation, the rays are predominantly incoherent, making impractical many of the methods that have made IRT possible. Two methods that have already shown promise in decreasing the computational time of the GI solution are interleaved sampling and adaptive rendering. Interleaved sampling is a generalized sampling scheme that smoothly blends between regular and irregular sampling while maintaining coherence. Adaptive rendering algorithms adjust rendering quality, non-uniformally, using a guidance scheme. While adaptive rendering has shown to provide speed-up when used for off-line rendering it has not been utilized in IRT due to its naturally incoherent nature. In this paper, we combine adaptive rendering and interleaved sampling within a component-based solution into a new approach we term adaptive interleaved sampling. This allows us to tailor new adaptive heuristics for interleaved sampling of the individual components of the GI solution significantly improving overall performance. We present a novel component-based IGI framework for which we achieve interactive frame rates for a range of effects such as indirect diffuse lighting, soft shadows and single scatter homogeneous participating media.
GPU-Assisted High Quality Particle Rendering
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Cha, Deukhyun; Son, Sungjin; Ihm, Insung
Visualizing dynamic participating media in particle form by fully solving equations from the light transport theory is a computationally very expensive process. In this paper, we present a computational pipeline for particle volume rendering that is easily accelerated by the current GPU. To fully harness its massively parallel computing power, we transform input particles into a volumetric density field using a GPU-assisted, adaptive density estimation technique that iteratively adapts the smoothing length for local grid cells. Then, the volume data is visualized efficiently based on the volume photon mapping method where our GPU techniques further improve the rendering quality offered by previous implementations while performing rendering computation in acceptable time. It is demonstrated that high quality volume renderings can be easily produced from large particle datasets in time frames of a few seconds to less than a minute.
A Framework for Interactive Hypertexture Modelling
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Gilet, G.; Dischler, J.M.
Hypertexturing can be a powerful way of adding rich geometric details to surfaces at low memory cost by using a procedural three-dimensional (3D) space distortion. However, this special kind of texturing technique still raises a major problem: the efficient control of the visual result. In this paper, we introduce a framework for interactive hypertexture modelling. This framework is based on two contributions. First, we propose a reformulation of the density modulation function. Our density modulation is based on the notion of shape transfer function. This function, which can be easily edited by users, allows us to control in an intuitive way the visual appearance of the geometric details resulting from the space distortion. Second, we propose to use a hybrid surface and volume-point-based representation in order to be able to dynamically hypertexture arbitrary objects at interactive frame rates. The rendering consists in a combined splat- and raycasting-based direct volume rendering technique. The splats are used to model the volumetric object while raycasting allows us to add the details. An experimental study on users shows that our approach improves the design of hypertextures and yet preserves their procedural nature.
Complex Barycentric Coordinates with Applications to Planar Shape Deformation
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Weber, Ofir; Ben-Chen, Mirela; Gotsman, Craig
GPU Rendering of Relief Mapped Conical Frusta
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Bhagvat, D.; Jeschke, S.; Cline, D.; Wonka, P.
This paper proposes to use relief-mapped conical frusta (cones cut by planes) to skin skeletal objects. Based on this representation, current programmable graphics hardware can perform the rendering with only minimal communication between the CPU and GPU. A consistent definition of conical frusta including texture parametrization and a continuous surface normal is provided. Rendering is performed by analytical ray casting of the relief-mapped frusta directly on the GPU. We demonstrate both static and animated objects rendered using our technique and compare to polygonal renderings of similar quality.
Progressive Lossless Mesh Compression Via Incremental Parametric Refinement
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Valette, Sebastien; Chaine, Raphaelle; Prost, Remy
In this paper, we propose a novel progressive lossless mesh compression algorithm based on Incremental Parametric Refinement, where the connectivity is uncontrolled in a first step, yielding visually pleasing meshes at each resolution level while saving connectivity information compared to previous approaches. The algorithm starts with a coarse version of the original mesh, which is further refined by means of a novel refinement scheme. The mesh refinement is driven by a geometric criterion, in spirit with surface reconstruction algorithms, aiming at generating uniform meshes. The vertices coordinates are also quantized and transmitted in a progressive way, following a geometric criterion, efficiently allocating the bit budget. With this assumption, the generated intermediate meshes tend to exhibit a uniform sampling. The potential discrepancy between the resulting connectivity and the original one is corrected at the end of the algorithm. We provide a proof-of-concept implementation, yielding very competitive results compared to previous works in terms of rate/distortion trade-off.
Scalable real-time animation of rivers
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Yu, Qizhi; Neyret, Fabrice; Bruneton, Eric; Holzschuch, Nicolas
Many recent games and applications target the interactive exploration of realistic large scale worlds. These worlds consist mostly of static terrain models, as the simulation of animated fluids in these virtual worlds is computationally expensive. Adding flowing fluids, such as rivers, to these virtual worlds would greatly enhance their realism, but causes specific issues: as the user is usually observing the world at close range, small scale details such as waves and ripples are important. However, the large scale of the world makes classical methods impractical for simulating these effects. In this paper, we present an algorithm for the interactive simulation of realistic flowing fluids in large virtual worlds. Our method relies on two key contributions: the local computation of the velocity field of a steady flow given boundary conditions, and the advection of small scale details on a fluid, following the velocity field, and uniformly sampled in screen space.
Exposure Fusion: A Simple and Practical Alternative to High Dynamic Range Photography
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Mertens, T.; Kautz, J.; Van Reeth, F.
We propose a technique for fusing a bracketed exposure sequence into a high quality image, without converting to High dynamic range (HDR) first. Skipping the physically based HDR assembly step simplifies the acquisition pipeline. This avoids camera response curve calibration and is computationally efficient. It also allows for including flash images in the sequence. Our technique blends multiple exposures, guided by simple quality measures like saturation and contrast. This is done in a multiresolution fashion to account for the brightness variation in the sequence. The resulting image quality is comparable to existing tone mapping operators.
Implicit Contact Handling for Deformable Objects
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Otaduy, Miguel A.; Tamstorf, Rasmus; Steinemann, Denis; Gross, Markus
We present an algorithm for robust and efficient contact handling of deformable objects. By being aware of the internal dynamics of the colliding objects, our algorithm provides smooth rolling and sliding, stable stacking, robust impact handling, and seamless coupling of heterogeneous objects, all in a unified manner. We achieve dynamicsawareness through a constrained dynamics formulation with implicit complementarity constraints, and we present two major contributions that enable an efficient solution of the constrained dynamics problem: a time stepping algorithm that robustly ensures non-penetration and progressively refines the formulation of constrained dynamics, and a new solver for large mixed linear complementarity problems, based on iterative constraint anticipation. We show the application of our algorithm in challenging scenarios such as multi-layered cloth moving at high velocities, or colliding deformable solids simulated with large time steps.
A Concise and Provably Informative Multi-Scale Signature Based on Heat Diffusion
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Sun, Jian; Ovsjanikov, Maks; Guibas, Leonidas
We propose a novel point signature based on the properties of the heat diffusion process on a shape. Our signature, called the Heat Kernel Signature (or HKS), is obtained by restricting the well-known heat kernel to the temporal domain. Remarkably we show that under certain mild assumptions, HKS captures all of the information contained in the heat kernel, and characterizes the shape up to isometry. This means that the restriction to the temporal domain, on the one hand, makes HKS much more concise and easily commensurable, while on the other hand, it preserves all of the information about the intrinsic geometry of the shape. In addition, HKS inherits many useful properties from the heat kernel, which means, in particular, that it is stable under perturbations of the shape. Our signature also provides a natural and efficiently computable multi-scale way to capture information about neighborhoods of a given point, which can be extremely useful in many applications. To demonstrate the practical relevance of our signature, we present several methods for non-rigid multi-scale matching based on the HKS and use it to detect repeated structure within the same shape and across a collection of shapes.
Specular Effects on the GPU: State of the Art
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Szirmay-Kalos, Laszlo; Umenhoffer, Tamas; Patow, Gustavo; Szecsi, Laszlo; Sbert, Mateu
This survey reviews algorithms that can render specular, i.e. mirror reflections, refractions, and caustics on the GPU. We establish a taxonomy of methods based on the three main different ways of representing the scene and computing ray intersections with the aid of the GPU, including ray tracing in the original geometry, ray tracing in the sampled geometry, and geometry transformation. Having discussed the possibilities of implementing ray tracing, we consider the generation of single reflections/refractions, interobject multiple reflections/refractions, and the general case which also includes self-reflections or refractions. Moving the focus from the eye to the light sources, caustic effect generation approaches are also examined.
GIzMOs: Genuine Image Mosaics with Adaptive Tiling
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Pavic, D.; Ceumern, U.; Kobbelt, L.
We present a method that splits an input image into a set of tiles. Each tile is then replaced by another image from a large database such that, when viewed from a distance, the original image is reproduced as well as possible. While the general concept of image mosaics is not new, we consider our results as genuine image mosaics (or short GIzMOs) in the sense that the images from the database are not modified in any way. This is different from previous work, where the image tiles are usually colour shifted or overlaid with the high-frequency content of the input image. Besides the regular alignment of the tiles we propose a greedy approach for adaptive tiling where larger tiles are placed in homogenous image regions. By this we avoid the visual periodicity, which is induced by the equal spacing of the image tiles in the completely regular setting. Our overall system addresses also the cleaning of the image database by removing all unwanted images with no meaningful content. We apply differently sophisticated image descriptors to find the best matching image for each tile. For aesthetic and artistic reasons we classify each tile as feature or non-feature and then apply a suitable image descriptor. In a user study we have verified that our descriptors lead to mosaics that are significantly better recognizable than just taking, e.g. average colour values.
Color correction for tone mapping
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Mantiuk, R.; Mantiuk, R.; Tomaszewska, A.; Heidrich, W.
Tone mapping algorithms offer sophisticated methods for mapping a real-world luminance range to the luminance range of the output medium but they often cause changes in color appearance. In this work we conduct a series of subjective appearance matching experiments to measure the change in image colorfulness after contrast compression and enhancement. The results indicate that the relation between contrast compression and the color saturation correction that matches color appearance is non-linear and smaller color correction is required for small change of contrast. We demonstrate that the relation cannot be fully explained by color appearance models. We propose color correction formulas that can be used with existing tone mapping algorithms. We extend existing global and local tone mapping operators and show that the proposed color correction formulas can preserve original image colors after tone scale manipulation.
Robust and Efficient Surface Reconstruction From Range Data
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Labatut, P.; Pons, J.-P.; Keriven, R.
We describe a robust but simple algorithm to reconstruct a surface from a set of merged range scans. Our key contribution is the formulation of the surface reconstruction problem as an energy minimisation problem that explicitly models the scanning process. The adaptivity of the Delaunay triangulation is exploited by restricting the energy to inside/outside labelings of Delaunay tetrahedra. Our energy measures both the output surface quality and how well the surface agrees with soft visibility constraints. Such energy is shown to perfectly fit into the minimum s - t cuts optimisation framework, allowing fast computation of a globally optimal tetrahedra labeling, while avoiding the shrinking bias that usually plagues graph cuts methods.The behaviour of our method confronted to noise, undersampling and outliers is evaluated on several data sets and compared with other methods through different experiments: its strong robustness would make our method practical not only for reconstruction from range data but also from typically more difficult dense point clouds, resulting for instance from stereo image matching. Our effective modeling of the surface acquisition inverse problem, along with the unique combination of Delaunay triangulation and minimum s - t cuts, makes the computational requirements of the algorithm scale well with respect to the size of the input point cloud.
Compression of Human Motion Capture Data Using Motion Pattern Indexing
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Gu, Qin; Peng, Jingliang; Deng, Zhigang
In this work, a novel scheme is proposed to compress human motion capture data based on hierarchical structure construction and motion pattern indexing. For a given sequence of 3D motion capture data of human body, the 3D markers are first organized into a hierarchy where each node corresponds to a meaningful part of the human body. Then, the motion sequence corresponding to each body part is coded separately. Based on the observation that there is a high degree of spatial and temporal correlation among the 3D marker positions, we strive to identify motion patterns that form a database for each meaningful body part. Thereafter, a sequence of motion capture data can be efficiently represented as a series of motion pattern indices. As a result, higher compression ratio has been achieved when compared with the prior art, especially for long sequences of motion capture data with repetitive motion styles. Another distinction of this work is that it provides means for flexible and intuitive global and local distortion controls.
Arches: a Framework for Modeling Complex Terrains
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Peytavie, A.; Galin, E.; Grosjean, J.; Merillou, S.
In this paper, we present a framework for representing complex terrains with such features as overhangs, arches and caves and including different materials such as sand and rocks. Our hybrid model combines a volumetric discrete data structure that stores the different materials and an implicit representation for sculpting and reconstructing the surface of the terrain. Complex scenes can be edited and sculpted interactively with high level tools. We also propose an original rock generation technique that enables us to automatically generate complex rocky sceneries with piles of rocks without any computationally demanding physically-based simulation.
Wipe-Off: An Intuitive Interface for Exploring Ultra-Large Multi-Spectral Data Sets for Cultural Heritage Diagnostics
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Ponto, K.; Seracini, M.; Kuester, F.
A visual analytics technique for the intuitive, hands-on analysis of massive, multi-dimensional and multi-variate data is presented. This multi-touch-based technique introduces a set of metaphors such as wiping, scratching, sandblasting, squeezing and drilling, which allow for rapid analysis of global and local characteristics in the data set, accounting for factors such as gesture size, pressure and speed. A case study is provided for the analysis of multi-spectral image data of cultural artefacts. By aligning multi-spectral layers in a stack, users can apply different multi-touch metaphors to investigate features across different wavelengths. With this technique, flexibly definable regions can be interrogated concurrently without affecting surrounding data.
Anomalous Dispersion in Predictive Rendering
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Weidlich, Andrea; Wilkie, Alexander
In coloured media, the index of refraction does not decrease monotonically with increasing wavelength, but behaves in a quite non-monotonical way. This behaviour is called anomalous dispersion and results from the fact that the absorption of a material influences its index of refraction.So far, this interesting fact has not been widely acknowledged by the graphics community. In this paper, we demonstrate how to calculate the correct refractive index for a material based on its absorption spectrum with the Kramers-Kronig relation, and we discuss for which types of objects this effect is relevant in practice.

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