32-Issue 7

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https://diglib.eg.org/handle/10.2312/185

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Boundary-Aware Extinction Mapping
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Gautron, Pascal; Delalandre, Cyril; Marvie, Jean-Eudes; Lecocq, Pascal; B. Levy, X. Tong, and K. Yin
We introduce Boundary-Aware Extinction Maps for interactive rendering of massive heterogeneous volumetric datasets. Our approach is based on the projection of the extinction along light rays into a boundary-aware function space, focusing on the most relevant sections of the light paths. This technique also provides an alternative representation of the set of participating media, allowing scattering simulation methods to be applied on arbitrary volume representations. Combined with a simple out-of-core rendering framework, Boundary-Aware Extinction Maps are valuable tools for interactive applications as well as production previsualization and rendering.
A GPU-based Streaming Algorithm for High-Resolution Cloth Simulation
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Tang, Min; Tong, Ruofeng; Narain, Rahul; Meng, Chang; Manocha, Dinesh; B. Levy, X. Tong, and K. Yin
We present a GPU-based streaming algorithm to perform high-resolution and accurate cloth simulation. We map all the components of cloth simulation pipeline, including time integration, collision detection, collision response, and velocity updating to GPU-based kernels and data structures. Our algorithm perform intra-object and inter-object collisions, handles contacts and friction, and is able to accurately simulate folds and wrinkles. We describe the streaming pipeline and address many issues in terms of obtaining high throughput on many-core GPUs. In practice, our algorithm can perform high-fidelity simulation on a cloth mesh with 2M triangles using 3GB of GPU memory. We highlight the parallel performance of our algorithm on three different generations of GPUs. On a high-end NVIDIA Tesla K20c, we observe up to two orders of magnitude performance improvement as compared to a single-threaded CPU-based algorithm, and about one order of magnitude improvement over a 16-core CPU-based parallel implementation.
Polar NURBS Surface with Curvature Continuity
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Shi, Kan-Le; Yong, Jun-Hai; Tang, Lei; Sun, Jia-Guang; Paul, Jean-Claude; B. Levy, X. Tong, and K. Yin
Polar NURBS surface is a kind of periodic NURBS surface, one boundary of which shrinks to a degenerate polar point. The specific topology of its control-point mesh offers the ability to represent a cap-like surface, which is common in geometric modeling. However, there is a critical and challenging problem that hinders its application: curvature continuity at the extraordinary singular pole. We first propose a sufficient and necessary condition of curvature continuity at the pole. Then, we present constructive methods for the two key problems respectively: how to construct a polar NURBS surface with curvature continuity and how to reform an ordinary polar NURBS surface to curvature continuous. The algorithms only depend on the symbolic representation and operations of NURBS, and they introduce no restrictions on the degree or the knot vectors. Examples and comparisons demonstrate the applications of the curvature-continuous polar NURBS surface in hole-filling and free-shape modeling.
Ontology-based Model for Chinese Calligraphy Synthesis
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Xia, Yang; Wu, Jiangqin; Gao, Pengcheng; Lin, Yuan; Mao, Tianjiao; B. Levy, X. Tong, and K. Yin
There are lots of digitized Chinese calligraphic works written by ancient calligraphists in CADAL. Sometimes users want to generate a tablet or a piece of calligraphic work written by these calligraphists. However, some characters had not been written by them or though were ever written but are hard to read because of long time weathering. Furthermore, different works of the same calligraphist may have diverse styles. It is a great challenge to generate a new calligraphic character with particular style. In this paper, we present a novel approach to synthesize regular script calligraphic characters in the style of some specific calligraphic works. Our approach first processes original calligraphic resources by multi-level segmentation. Then, a domain ontology is established to supervise basic resources and to provide significant support for calligraphy synthesis. Finally, a novel algorithm is proposed to synthesize new calligraphic characters. We demonstrate the effectiveness of our method by showing various synthesized results in the style of different calligraphic works of Liu Gongquan.
A Progressive Tri-level Segmentation Approach for Topology-Change-Aware Video Matting
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Ju, Jinlong; Wang, Jue; Liu, Yebin; Wang, Haoqian; Dai, Qionghai; B. Levy, X. Tong, and K. Yin
Previous video matting approaches mostly adopt the ''binary segmentation + matting'' strategy, i.e., first segment each frame into foreground and background regions, then extract the fine details of the foreground boundary using matting techniques. This framework has several limitations due to the fact that binary segmentation is employed. In this paper, we propose a new supervised video matting approach. Instead of applying binary segmentation, we explicitly model segmentation uncertainty in a novel tri-level segmentation procedure. The segmentation is done progressively, enabling us to handle difficult cases such as large topology changes, which are challenging to previous approaches. The tri-level segmentation results can be naturally fed into matting techniques to generate the final alpha mattes. Experimental results show that our system can generate high quality results with less user inputs than the state-of-the-art methods.
A Programmable Graphics Processor based on Partial Stream Rewriting
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Middendorf, Lars; Haubelt, Christian; B. Levy, X. Tong, and K. Yin
Current graphics processing units (GPU) typically offer only a limited number of programmable pipeline stages, whose usage, data flow and topology are mostly fixed. Although a more flexible, custom rendering pipeline can be emulated using the compute functionality of existing GPUs, this approach requires to manage work queues, synchronization, and scheduling in software. In this paper, we present a hardware architecture for a novel, programmable rendering pipeline, which is based on a circulating stream of data and control tokens that are iteratively modified via pattern matching. Our architecture provides light-weight mechanisms for dynamic thread creation, lock-free synchronization, and scheduling to support recursion, dynamic shader linkage and custom primitive types. A hardware prototype, running complex examples, demonstrates the improved reconfigurability also the scalability of our graphics architecture.
Efficient Smoke Simulation on Curvilinear Grids
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Azevedo, Vinicius C.; Oliveira, Manuel M.; B. Levy, X. Tong, and K. Yin
We present an efficient approach for performing smoke simulation on curvilinear grids. Our technique is based on a fast unconditionally-stable advection algorithm and on a new and efficient solution to enforce mass conservation. It uses a staggered-grid variable arrangement, and has linear cost on the number of grid cells. Our method naturally integrates itself with overlapping-grid techniques, lending to an efficient way of producing highly-realistic animations of dynamic scenes. Compared to approaches based on regular grids traditionally used in computer graphics, our method allows for better representation of boundary conditions, with just a small increment in computational cost. Thus, it can be used to evaluate aerodynamic properties, possibly enabling unexplored applications in computer graphics, such as interactive computation of lifting forces on complex objects.We demonstrate the effectiveness of our approach, both in 2-D and 3-D, through a variety of high-quality smoke animations.
Artistic QR Code Embellishment
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Lin, Yi-Shan; Luo, Sheng-Jie; Chen, Bing-Yu; B. Levy, X. Tong, and K. Yin
A QR code is a two-dimensional barcode that encodes information. A standard QR code contains only regular black and white squares, and thus is unattractive. This paper proposes a novel framework for embellishing a standard QR code, to make it both attractive and recognizable by any human while maintaining its scanability. The proposed method is inspired by artistic methods. A QR code is typically embellished by stylizing the squares and embedding images into it. In the proposed framework, the regular squares are reshaped using a binary examplar, to make their local appearances resemble the example shape. Additionally, an error-aware warping technique for deforming the embedded image is proposed; it minimizes the error in the QR code that is generated by the embedding of the image to optimize the readability of the code. The proposed algorithm yields lower data error than previous global transformation techniques because the warping can locally deform the embedded image to conform to the squares that surround it. The proposed framework was examined by using it to embellish an extensive set of QR codes and to test the readability with various commercial QR code readers.
Eye-Centered Color Adaptation in Global Illumination
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Gruson, Adrien; Ribardière, Mickael; Cozot, Remi; B. Levy, X. Tong, and K. Yin
Color adaptation is a well known ability of the human visual system (HVS). Colors are perceived as constant even though the illuminant color changes. Indeed, the perceived color of a diffuse white sheet of paper is still white even though it is illuminated by a single orange tungsten light, whereas it is orange from a physical point of view. Unfortunately global illumination algorithms only focus on the physics aspects of light transport. The ouput of a global illuminantion engine is an image which has to undergo chromatic adaptation to recover the color as perceived by the HVS. In this paper, we propose a new color adaptation method well suited to global illumination. This method estimates the adaptation color by averaging the irradiance color arriving at the eye. Unlike other existing methods, our approach is not limited to the view frustrum, as it considers the illumination from all the scene. Experiments have shown that our method outperforms the state of the art methods.
Garment Modeling from a Single Image
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Zhou, Bin; Chen, Xiaowu; Fu, Qiang; Guo, Kan; Tan, Ping; B. Levy, X. Tong, and K. Yin
Modeling of realistic garments is essential for online shopping and many other applications including virtual characters. Most of existing methods either require a multi-camera capture setup or a restricted mannequin pose. We address the garment modeling problem according to a single input image. We design an all-pose garment outline interpretation, and a shading-based detail modeling algorithm. Our method first estimates the mannequin pose and body shape from the input image. It further interprets the garment outline with an oriented facet decided according to the mannequin pose to generate the initial 3D garment model. Shape details such as folds and wrinkles are modeled by shape-from-shading techniques, to improve the realism of the garment model. Our method achieves similar result quality as prior methods from just a single image, significantly improving the flexibility of garment modeling.
Adaptive Ray-bundle Tracing with Memory Usage Prediction: Efficient Global Illumination in Large Scenes
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Tokuyoshi, Yusuke; Sekine, Takashi; Silva, Tiago da; Kanai, Takashi; B. Levy, X. Tong, and K. Yin
This paper proposes an adaptive rendering technique for ray-bundle tracing. Ray-bundle tracing can be done by per-pixel linked-list construction on a GPU rasterization pipeline. This rasterization based approach offers significant benefits for the efficient generation of light maps (e.g., hardware acceleration, tessellation, and recycling of shaders used in real-time graphics). However, it is inapplicable to large and complex scenes due to the limited capacity of the GPU memory because it requires a high-resolution frame buffer and high-capacity node buffer for the linked-lists. In addition, memory overflow can potentially occur on the per-pixel linked-list since the memory usage of the lists is usually unknown before the rendering process. We introduce an adaptive tiling technique with memory usage prediction. Our method uses an appropriately tiled frame buffer, thus eliminating almost all of the overflow risks thanks to our adaptive tile subdivision scheme. Using this technique, we are able to render high-quality light maps of large and complex scenes which cannot be computed using previous ray-bundle based methods.
Animated 3D Line Drawings with Temporal Coherence
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Xu, Xiang; Seah, Hock Soon; Quah, Chee Kwang; B. Levy, X. Tong, and K. Yin
Producing traditional animation is a laborious task where the key drawings are first drawn by artists and thereafter inbetween drawings are created, whether it is by hand or computer-assisted. Auto-inbetweening of these 2D key drawings by computer is a non-trivial task as 3D depths are missing. An alternate approach is to generate all the drawings by extracting lines directly from animated 3D models frame by frame, concatenating and rendering them together into an animation. However, animation quality generated using this straightforward method bears two problems. Firstly, the animation contains unsatisfactory visual artifacts such as line flickering and popping. This is especially pronounced when the lines are extracted using high-order derivatives, such as ridges and valleys, from 3D models represented in triangle meshes. Secondly, there is a lack of temporal continuity as each drawing is generated without taking its neighboring drawings into consideration. In this paper, we propose an improved approach over the straightforward method by transferring extracted 3D line drawings of each frame into individual 3D lines and processing them along the time domain. Our objective is to minimize the visual artifacts and incorporate temporal relationship of individual lines throughout the entire animation sequence. This is achieved by creating correspondent trajectory of each line from each frame and applying global optimization on each trajectory. To realize this target, we present a fully automatic novel approach, which consists of (1) a line matching algorithm, (2) an optimizing algorithm, taking into account both the variations of numbers and lengths of 3D lines in each frame, and (3) a robust tracing method for transferring collections of line segments extracted from the 3D models into individual lines. We evaluate our approach on several animated model sequences to demonstrate its effectiveness in producing line drawing animations with temporal coherence.
Efficient Shadow Removal Using Subregion Matching Illumination Transfer
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Xiao, Chunxia; Xiao, Donglin; Zhang, Ling; Chen, Lin; B. Levy, X. Tong, and K. Yin
This paper proposes a new shadow removal approach for input single natural image by using subregion matching illumination transfer. We first propose an effective and automatic shadow detection algorithm incorporating global successive thresholding scheme and local boundary refinement. Then we present a novel shadow removal algorithm by performing illumination transfer on the matched subregion pairs between the shadow regions and non-shadow regions, and this method can process complex images with different kinds of shadowed texture regions and illumination conditions. In addition, we develop an efficient shadow boundary processing method by using alpha matte interpolation, which produces seamless transition between the shadow and non-shadow regions. Experimental results demonstrate the capabilities of our algorithm in both the shadow removal quality and performance.
A Semi-Lagrangian Closest Point Method for Deforming Surfaces
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Auer, Stefan; Westermann, Rüdiger; B. Levy, X. Tong, and K. Yin
We present an Eulerian method for the real-time simulation of intrinsic fluid dynamics effects on deforming surfaces. Our method is based on a novel semi-Lagrangian closest point method for the solution of partial differential equations on animated triangle meshes.We describe this method and demonstrate its use to com- pute and visualize flow and wave propagation along such meshes at high resolution and speed. Underlying our technique is the efficient conversion of an animated triangle mesh into a time-dependent implicit repre- sentation based on closest surface points. The proposed technique is unconditionally stable with respect to the surface deformation and, in contrast to comparable Lagrangian techniques, its precision does not depend on the level of detail of the surface triangulation.
Constrainable Multigrid for Cloth
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Jeon, Inyong; Choi, Kwang-Jin; Kim, Tae-Yong; Choi, Bong-Ouk; Ko, Hyeong-Seok; B. Levy, X. Tong, and K. Yin
We present a new technique which can handle both point and sliding constraints in the multigrid (MG) framework. Although the MG method can theoretically perform as fast as O(N), the development of a clothing simulator based on the MG method calls for solving an important technical challenge: handling the constraints. Resolving constrains has been difficult in MG because there has been no clear way to transfer the constraints existing in the finest level mesh to the coarser level meshes. This paper presents a new formulation based on soft constraints, which can coarsen the constraints defined in the finest level to the coarser levels. Experiments are performed which show that the proposed method can solve the linear system up to 4-9 times faster in comparison with the modified preconditioned conjugate gradient method (MPCG) without quality degradation. The proposed method is easy to implement and can be straightforwardly applied to existing clothing simulators which are based on implicit time integration.
Second-Order Approximation for Variance Reduction in Multiple Importance Sampling
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Lu, Heqi; Pacanowski, Romain; Granier, Xavier; B. Levy, X. Tong, and K. Yin
Monte Carlo Techniques are widely used in Computer Graphics to generate realistic images. Multiple Importance Sampling reduces the impact of choosing a dedicated strategy by balancing the number of samples between different strategies. However, an automatic choice of the optimal balancing remains a difficult problem. Without any scene characteristics knowledge, the default choice is to select the same number of samples from different strategies and to use them with heuristic techniques (e.g., balance, power or maximum). In this paper, we introduce a second-order approximation of variance for balance heuristic. Based on this approximation, we introduce an automatic distribution of samples for direct lighting without any prior knowledge of the scene characteristics. We demonstrate that for all our test scenes (with different types of materials, light sources and visibility complexity), our method actually reduces variance in average.We also propose an implementation with low overhead for offline and GPU applications. We hope that this approach will help developing new balancing strategies.
Coarse-to-Fine Normal Filtering for Feature-Preserving Mesh Denoising Based on Isotropic Subneighborhoods
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Zhu, Lei; Wie, Mingqiang; Yu, Jinze; Wang, Weiming; Qin, Jing; Heng, Pheng-Ann; B. Levy, X. Tong, and K. Yin
State-of-the-art normal filters usually denoise each face normal using its entire anisotropic neighborhood. However, enforcing these filters indiscriminately on the anisotropic neighborhood will lead to feature blurring, especially in challenging regions with shallow features. We develop a novel mesh denoising framework which can effectively preserve features with various sizes. Our idea is inspired by the observation that the underlying surface of a noisy mesh is piecewise smooth. In this regard, it is more desirable that we denoise each face normal within its piecewise smooth region (we call such a region as an isotropic subneighborhood) instead of using the anisotropic neighborhood. To achieve this, we first classify mesh faces into several types using a face normal tensor voting and then perform a normal filter to obtain a denoised coarse normal field. Based on the results of normal classification and the denoised coarse normal field, we segment the anisotropic neighborhood of every feature face into a number of isotropic subneighborhoods via local spectral clustering. Thus face normal filtering can be performed again on the isotropic subneighborhoods and produce a more accurate normal field. Extensive tests on various models demonstrate that our method can achieve better performance than state-of-the-art normal filters, especially in challenging regions with features.
As-Rigid-As-Possible Distance Field Metamorphosis
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Weng, Yanlin; Chai, Menglei; Xu, Weiwei; Tong, Yiying; Zhou, Kun; B. Levy, X. Tong, and K. Yin
Widely used for morphing between objects with arbitrary topology, distance field interpolation (DFI) handles topological transition naturally without the need for correspondence or remeshing, unlike surface-based interpolation approaches. However, lack of correspondence in DFI also leads to ineffective control over the morphing process. In particular, unless the user specifies a dense set of landmarks, it is not even possible to measure the distortion of intermediate shapes during interpolation, let alone control it. To remedy such issues, we introduce an approach for establishing correspondence between the interior of two arbitrary objects, formulated as an optimal mass transport problem with a sparse set of landmarks. This correspondence enables us to compute non-rigid warping functions that better align the source and target objects as well as to incorporate local rigidity constraints to perform as-rigid-as-possible DFI. We demonstrate how our approach helps achieve flexible morphing results with a small number of landmarks.
Multiplane Video Stabilization
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Wang, Zhong-Qiang; Zhang, Lei; Huang, Hua; B. Levy, X. Tong, and K. Yin
This paper presents a novel video stabilization approach by leveraging the multiple planes structure of video scene to stabilize inter-frame motion. As opposed to previous stabilization procedure operating in a single plane, our approach primarily deals with multiplane videos and builds their multiple planes structure for performing stabilization in respective planes. Hence, a robust plane detection scheme is devised to detect multiple planes by classifying feature trajectories according to reprojection errors generated by plane induced homographies. Then, an improved planar stabilization technique is applied by conforming to the compensated homography in each plane. Finally, multiple stabilized planes are coherently fused by content-preserving image warps to obtain the output stabilized frames. Our approach does not need any stereo reconstruction, yet is able to produce commendable results due to awareness of multiple planes structure in the stabilization. Experimental results demonstrate the effectiveness and efficiency of our approach to robust stabilization on multiplane videos.
An Efficient and Scalable Image Filtering Framework Using VIPS Fusion
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Zhang, Jun; Chen, Xiuhong; Zhao, Yan; Li, H.; B. Levy, X. Tong, and K. Yin
Edge-preserving image filtering is a valuable tool for a variety of applications in image processing and computer vision. Motivated by a new simple but effective local Laplacian filter, we propose a scalable and efficient image filtering framework to extend this edge-preserving image filter and construct an uniform implementation in O(N) time. The proposed framework is built upon a practical global-to-local strategy. The input image is first remapped globally by a series of tentative remapping functions to generate a virtual candidate image sequence (Virtual Image Pyramid Sequence, VIPS). This sequence is then recombined locally to a single output image by a flexible edge-aware pixel-level fusion rule. To avoid halo artifacts, both the output image and the virtual candidate image sequence are transformed into multi-resolution pyramid representations. Four examples, single image de-hazing, multi-exposure fusion, fast edge-preserving filtering and tone-mapping, are presented as the concrete applications of the proposed framework. Experiments on filtering effect and computational efficiency indicate that the proposed framework is able to build a wide range of fast image filtering that yields visually compelling results.

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