32-Issue 7

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

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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.
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.
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.
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.
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.
Combustion Waves on the Point Set Surface
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Jeong, SoHyeon; Kim, Chang-Hun; B. Levy, X. Tong, and K. Yin
This paper introduces a combustion model of heat transfer and fuel consumption for the propagation of a fire front on a point cloud surface. The heat transfer includes the heat advection by the airflow as well as diffusion, chemical reaction, and heat loss to generate complex, but controllable heat flows with a designed airflow velocity. For the stable heat advection, we solve a semi-Lagrangian method on point samples using discrete exponential maps to trace the position from which the wind blows while preserving the geodesic distance. We also propose angular Voronoi weights for a discrete Laplace-Beltrami operator that shows better isotropic diffusion on the inhomogeneous distribution of point clouds than the cotangent or moving least-squares schemes. We demonstrate a diversity of burning scenarios by incorporating factors affecting the fire spreading such as buoyancy and object geometries in the airflow velocity fields, or by synthesizing patterns.
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.
Dynamic Comics for Hierarchical Abstraction of 3D Animation Data
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Choi, Myung Geol; Noh, Seung-Tak; Komura, Taku; Igarashi, Takeo; B. Levy, X. Tong, and K. Yin
Image storyboards of films and videos are useful for quick browsing and automatic video processing. A common approach for producing image storyboards is to display a set of selected key-frames in temporal order, which has been widely used for 2D video data. However, such an approach cannot be applied for 3D animation data because different information is revealed by changing parameters such as the viewing angle and the duration of the animation. Also, the interests of the viewer may be different from person to person. As a result, it is difficult to draw a single image that perfectly abstracts the entire 3D animation data. In this paper, we propose a system that allows users to interactively browse an animation and produce a comic sequence out of it. Each snapshot in the comic optimally visualizes a duration of the original animation, taking into account the geometry and motion of the characters and objects in the scene. This is achieved by a novel algorithm that automatically produces a hierarchy of snapshots from the input animation. Our user interface allows users to arrange the snapshots according to the complexity of the movements by the characters and objects, the duration of the animation and the page area to visualize the comic sequence. Our system is useful for quickly browsing through a large amount of animation data and semi-automatically synthesizing a storyboard from a long sequence of animation.
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.
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.
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.
EnvyDepth: An Interface for Recovering Local Natural Illumination from Environment Maps
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Banterle, Francesco; Callieri, Marco; Dellepiane, Matteo; Corsini, Massimiliano; Pellacini, Fabio; Scopigno, Roberto; B. Levy, X. Tong, and K. Yin
In this paper, we present EnvyDepth, an interface for recovering local illumination from a single HDR environment map. In EnvyDepth, the user quickly indicates strokes to mark regions of the environment map that should be grouped together in a single geometric primitive. From these annotated strokes, EnvyDepth uses edit propagation to create a detailed collection of virtual point lights that reproduce both the local and the distant lighting effects in the original scene. When compared to the sole use of the distant illumination, the added spatial information better reproduces a variety of local effects such as shadows, highlights and caustics. Without the effort needed to create precise scene reconstructions, EnvyDepth annotations take only tens of seconds to produce a plausible lighting without visible artifacts. This is easy to obtain even in the case of complex scenes, both indoors and outdoors. The generated lighting environments work well in a production pipeline since they are efficient to use and able to produce accurate renderings.
Evaluation of Tone Mapping Operators for HDR-Video
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Eilertsen, Gabriel; Wanat, Robert; Mantiuk, Rafal K.; Unger, Jonas; B. Levy, X. Tong, and K. Yin
Eleven tone-mapping operators intended for video processing are analyzed and evaluated with camera-captured and computer-generated high-dynamic-range content. After optimizing the parameters of the operators in a formal experiment, we inspect and rate the artifacts (flickering, ghosting, temporal color consistency) and color rendition problems (brightness, contrast and color saturation) they produce. This allows us to identify major problems and challenges that video tone-mapping needs to address. Then, we compare the tone-mapping results in a pair-wise comparison experiment to identify the operators that, on average, can be expected to perform better than the others and to assess the magnitude of differences between the best performing operators.
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.
Fast Image-Based Modeling of Astronomical Nebulae
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Wenger, Stephan; Lorenz, Dirk; Magnor, Marcus; B. Levy, X. Tong, and K. Yin
Astronomical nebulae are among the most complex and visually appealing phenomena known outside the bounds of the Solar System. However, our fixed vantage point on Earth limits us to a single known view of these objects, and their intricate volumetric structure cannot be recovered directly. Recent approaches to reconstructing a volumetric 3D model use the approximate symmetry inherent to many nebulae, but require several hours of computation time on large multi-GPU clusters. We present a novel reconstruction algorithm based on group sparsity that reaches or even exceeds the quality of prior results while taking only a fraction of the time on a conventional desktop PC, thereby enabling end users in planetariums or educational facilities to produce high-quality content without expensive hardware or manual modeling. In principle, our approach can be generalized to other transparent phenomena with arbitrary types of user-specified symmetries.
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.
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.
Guided Real-Time Scanning of Indoor Objects
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Kim, Young Min; Mitra, Niloy J.; Huang, Qixing; Guibas, Leonidas; B. Levy, X. Tong, and K. Yin
Advances in 3D acquisition devices provide unprecedented opportunities for quickly scanning indoor environments. Such raw scans, however, are often noisy, incomplete, and significantly corrupted, making semantic scene understanding difficult, if not impossible. Unfortunately, in most existing workflows, scan quality is assessed after the scanning stage is completed, making it cumbersome to correct for significant missing data by additional scanning. In this work, we present a guided real-time scanning setup, wherein the incoming 3D data stream is continuously analyzed, and the data quality is automatically assessed. While the user is scanning an object, the proposed system discovers and highlights potential missing parts, thus guiding the operator (or an autonomous robot) as where to scan next. The proposed system assesses the quality and completeness of the 3D scan data by comparing to a large collection of commonly occurring indoor man-made objects using an efficient, robust, and effective scan descriptor. We have tested the system on a large number of simulated and real setups, and found the guided interface to be effective even in cluttered and complex indoor environments.
Hair Interpolation for Portrait Morphing
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Weng, Yanlin; Wang, Lvdi; Li, Xiao; Chai, Menglei; Zhou, Kun; B. Levy, X. Tong, and K. Yin
In this paper we study the problem of hair interpolation: given two 3D hair models, we want to generate a sequence of intermediate hair models that transform from one input to another both smoothly and aesthetically pleasing. We propose an automatic method that efficiently calculates a many-to-many strand correspondence between two or more given hair models, taking into account the multi-scale clustering structure of hair. Experiments demonstrate that hair interpolation can be used for producing more vivid portrait morphing effects and enabling a novel example-based hair styling methodology, where a user can interactively create new hairstyles by continuously exploring a ''style space'' spanning multiple input hair models.

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