30-Issue 7

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https://diglib.eg.org/handle/10.2312/167

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    Computing 3D Shape Guarding and Star Decomposition
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Yu, Wuyi; Li, Xin; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    This paper proposes an effective framework to compute the visibility guarding and star decomposition of 3D solid shapes. We propose a progressive integer linear programming algorithm to solve the guarding points that can visibility cover the entire shape; we also develop a constrained region growing scheme seeded on these guarding points to get the star decomposition. We demonstrate this guarding/decomposition framework can benefit graphics tasks such as shape interpolation and shape matching/retrieval
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    A Single Image Representation Model for Efficient Stereoscopic Image Creation
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Kim, Younghui; Jung, Hwi-ryong; Choi, Sungwoo; Lee, Jungjin; Noh, Junyong; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    Computer graphics is one of the most efficient ways to create a stereoscopic image. The process of stereoscopic CG generation is, however, still very inefficient compared to that of monoscopic CG generation. Despite that stereo images are very similar to each other, they are rendered and manipulated independently. Additional requirements for disparity control specific to stereo images lead to even greater inefficiency. This paper proposes a method to reduce the inefficiency accompanied in the creation of a stereoscopic image. The system automatically generates an optimized single image representation of the entire visible area from both cameras. The single image can be easily manipulated with conventional techniques, as it is spatially smooth and maintains the original shapes of scene objects. In addition, a stereo image pair can be easily generated with an arbitrary disparity setting. These convenient and efficient features are achieved by the automatic generation of a stereo camera pair, robust occlusion detection with a pair of Z-buffers, an optimization method for spatial smoothness, and stereo image pair generation with a non-linear disparity adjustment. Experiments show that our technique dramatically improves the efficiency of stereoscopic image creation while preserving the quality of the results.
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    Intelligent GPGPU Classification in Volume Visualization: A framework based on Error-Correcting Output Codes
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Escalera, Sergio; Puig, Anna; Amoros, Oscar; Salamó, Maria; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    In volume visualization, the definition of the regions of interest is inherently an iterative trial-and-error process finding out the best parameters to classify and render the final image. Generally, the user requires a lot of expertise to analyze and edit these parameters through multi-dimensional transfer functions. In this paper, we present a framework of intelligent methods to label on-demand multiple regions of interest. These methods can be split into a two-level GPU-based labelling algorithm that computes in time of rendering a set of labelled structures using the Machine Learning Error-Correcting Output Codes (ECOC) framework. In a pre-processing step, ECOC trains a set of Adaboost binary classifiers from a reduced pre-labelled data set. Then, at the testing stage, each classifier is independently applied on the features of a set of unlabelled samples and combined to perform multi-class labelling. We also propose an alternative representation of these classifiers that allows to highly parallelize the testing stage. To exploit that parallelism we implemented the testing stage in GPU-OpenCL. The empirical results on different data sets for several volume structures shows high computational performance and classification accuracy.
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    Interactive Indirect Illumination Using Voxel Cone Tracing
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Crassin, Cyril; Neyret, Fabrice; Sainz, Miguel; Green, Simon; Eisemann, Elmar; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    Indirect illumination is an important element for realistic image synthesis, but its computation is expensive and highly dependent on the complexity of the scene and of the BRDF of the involved surfaces. While off-line computation and pre-baking can be acceptable for some cases, many applications (games, simulators, etc.) require real-time or interactive approaches to evaluate indirect illumination. We present a novel algorithm to compute indirect lighting in real-time that avoids costly precomputation steps and is not restricted to low-frequency illumination. It is based on a hierarchical voxel octree representation generated and updated on the fly from a regular scene mesh coupled with an approximate voxel cone tracing that allows for a fast estimation of the visibility and incoming energy. Our approach can manage two light bounces for both Lambertian and glossy materials at interactive framerates (25-70FPS). It exhibits an almost scene-independent performance and can handle complex scenes with dynamic content thanks to an interactive octree-voxelization scheme. In addition, we demonstrate that our voxel cone tracing can be used to efficiently estimate Ambient Occlusion.
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    Motion Retrieval Using Low-Rank Subspace Decomposition of Motion Volume
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Sun, Chuan; Junejo, Imran; Foroosh, Hassan; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    This paper proposes a novel framework that allows for a flexible and an efficient retrieval of motion capture data in huge databases. The method first converts an action sequence into a novel representation, i.e. the Self-Similarity Matrix (SSM), which is based on the notion of self-similarity. This conversion of the motion sequences into compact and low-rank subspace representations greatly reduces the spatiotemporal dimensionality of the sequences. The SSMs are then used to construct order-3 tensors, and we propose a low-rank decomposition scheme that allows for converting the motion sequence volumes into compact lower dimensional representations, without losing the nonlinear dynamics of the motion manifold. Thus, unlike existing linear dimensionality reduction methods that distort the motion manifold and lose very critical and discriminative components, the proposed method performs well even when inter-class differences are small or intra-class differences are large. In addition, the method allows for an efficient retrieval and does not require the time-alignment of the motion sequences. We evaluate the performance of our retrieval framework on the CMU mocap dataset under two experimental settings, both demonstrating promising retrieval rates.
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    Flexible Splicing of Upper-Body Motion Spaces on Locomotion
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Basten, Ben J. H. van; Egges, Arjan; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    This paper presents an efficient technique for synthesizing motions by stitching, or splicing, an upper-body motion retrieved from a motion space on top of an existing lower-body locomotion of another motion. Compared to the standard motion splicing problem, motion space splicing imposes new challenges as both the upper and lower body motions might not be known in advance. Our technique is the first motion (space) splicing technique that propagates temporal and spatial properties of the lower-body locomotion to the newly generated upper-body motion and vice versa. Whereas existing techniques only adapt the upper-body motion to fit the lower-body motion, our technique also adapts the lower-body locomotion based on the upper body task for a more coherent full-body motion. In this paper, we will show that our decoupled approach is able to generate high-fidelity full-body motion for interactive applications such as games.
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    Motion Deblurring from a Single Image using Circular Sensor Motion
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Bando, Yosuke; Chen, Bing-Yu; Nishita, Tomoyuki; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    Image blur caused by object motion attenuates high frequency content of images, making post-capture deblurring an ill-posed problem. The recoverable frequency band quickly becomes narrower for faster object motion as high frequencies are severely attenuated and virtually lost. This paper proposes to translate a camera sensor circularly about the optical axis during exposure, so that high frequencies can be preserved for a wide range of in-plane linear object motion in any direction within some predetermined speed. That is, although no object may be photographed sharply at capture time, differently moving objects captured in a single image can be deconvolved with similar quality. In addition, circular sensor motion is shown to facilitate blur estimation thanks to distinct frequency zero patterns of the resulting motion blur point-spread functions. An analysis of the frequency characteristics of circular sensor motion in relation to linear object motion is presented, along with deconvolution results for photographs captured with a prototype camera.
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    Edge-Optimized À-Trous Wavelets for Local Contrast Enhancement with Robust Denoising
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Hanika, Johannes; Dammertz, Holger; Lensch, Hendrik; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    In this paper we extend the edge-avoiding à-trous wavelet transform for local contrast enhancement while avoiding common artifacts such as halos and gradient reversals. We show that this algorithm is a highly efficient and robust tool for image manipulation based on multi-scale decompositions. It can achieve comparable results to previous high-quality methods while being orders of magnitude faster and simpler to implement. Our method is much more robust than previously known fast methods by avoiding aliasing and ringing which is achieved by introducing a data-adaptive edge weight. Operating on multi-scale, our algorithm can directly include the BayesShrink method for denoising. For moderate noise levels our edge-optimized technique consistently improves separation of signal and noise.
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    Video Brush: A Novel Interface for Efficient Video Cutout
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Tong, Ruo-Feng; Zhang, Yun; Ding, Meng; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    We present Video Brush, a novel interface for interactive video cutout. Inspired by the progressive selection scheme in images, our interface is designed to select video objects by painting on successive frames as the video plays. The video objects are progressively selected by solving the graph-cut based local optimization according to the strokes drawn by the brush on each painted frame. In order to provide users interactive feedback, we accelerate 3D graph-cut by efficient graph building and multi-level banded graph-cut. Experimental results show that our novel interface is both intuitive and efficient for video cutout.
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    Creating Fluid Animation from a Single Image using Video Database
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Okabe, Makoto; Anjyo, Ken; Onai, Rikio; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    We present a method for synthesizing fluid animation from a single image, using a fluid video database. The user inputs a target painting or photograph of a fluid scene along with its alpha matte that extracts the fluid region of interest in the scene. Our approach allows the user to generate a fluid animation from the input image and to enter a few additional commands about fluid orientation or speed. Employing the database of fluid examples, the core algorithm in our method then automatically assigns fluid videos for each part of the target image. Our method can therefore deal with various paintings and photographs of a river, waterfall, fire, and smoke. The resulting animations demonstrate that our method is more powerful and efficient than our prior work.
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    Improving Performance and Accuracy of Local PCA
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Gassenbauer, Václav; Krivánek, Jaroslav; Bouatouch, Kadi; Bouville, Christian; Ribardière, Mickaël; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    Local Principal Component Analysis (LPCA) is one of the popular techniques for dimensionality reduction and data compression of large data sets encountered in computer graphics. The LPCA algorithm is a variant of kmeans clustering where the repetitive classification of high dimensional data points to their nearest cluster leads to long execution times. The focus of this paper is on improving the efficiency and accuracy of LPCA. We propose a novel SortCluster LPCA algorithm that significantly reduces the cost of the point-cluster classification stage, achieving a speed-up of up to 20. To improve the approximation accuracy, we investigate different initialization schemes for LPCA and find that the k-means++ algorithm [AV07] yields best results, however at a high computation cost. We show that similar ideas that lead to the efficiency of our SortCluster LPCA algorithm can be used to accelerate k-means++. The resulting initialization algorithm is faster than purely random seeding while producing substantially more accurate data approximation.
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    Exposure Fusion for Time-Of-Flight Imaging
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Hahne, Uwe; Alexa, Marc; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    This work deals with the problem of automatically choosing the correct exposure (or integration) time for timeof- flight depth image capturing. We apply methods known from high dynamic range imaging to combine depth images taken with differing integration times in order to produce high quality depth maps. We evaluate the quality of these depth maps by comparing the performance in reconstruction of planar textured patches and in the 3D reconstruction of an indoor scene. Our solution is fast enough to capture the images at interactive frame rates and also flexible to deal with any amount of exposures.
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    Efficient Opacity Specification Based on Feature Visibilities in Direct Volume Rendering
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Wang, Yunhai; Zhang, Jian; Chen, Wei; Zhang, Huai; Chi, Xuebin; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    Due to 3D occlusion, the specification of proper opacities in direct volume rendering is a time-consuming and unintuitive process. The visibility histograms introduced by Correa and Ma reflect the effect of occlusion by measuring the influence of each sample in the histogram to the rendered image. However, the visibility is defined on individual samples, while volume exploration focuses on conveying the spatial relationships between features. Moreover, the high computational cost and large memory requirement limits its application in multi-dimensional transfer function design. In this paper, we extend visibility histograms to feature visibility, which measures the contribution of each feature in the rendered image. Compared to visibility histograms, it has two distinctive advantages for opacity specification. First, the user can directly specify the visibilities for features and the opacities are automatically generated using an optimization algorithm. Second, its calculation requires only one rendering pass with no additional memory requirement. This feature visibility based opacity specification is fast and compatible with all types of transfer function design. Furthermore, we introduce a two-step volume exploration scheme, in which an automatic optimization is first performed to provide a clear illustration of the spatial relationship and then the user adjusts the visibilities directly to achieve the desired feature enhancement. The effectiveness of this scheme is demonstrated by experimental results on several volumetric datasets.
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    Authoring Hierarchical Road Networks
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Galin, Eric; Peytavie, Adrien; Guérin, Eric; Benes, Bedrich; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    We present a procedural method for generating hierarchical road networks connecting cities, towns and villages over large terrains. Our approach relies on an original geometric graph generation algorithm based on a non- Euclidean metric combined with a path merging algorithm that creates junctions between the different types of roads. Unlike previous work, our method allows high level user control by manipulating the density and the pattern of the network. The geometry of the highways, primary and secondary roads as well as the interchanges and intersections are automatically created from the graph structure by instantiating generic parameterized models.
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    Real Time Edit Propagation by Efficient Sampling
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Bie, Xiaohui; Huang, Haoda; Wang, Wencheng; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    It is popular to edit the appearance of images using strokes, owing to their ease of use and convenience of conveying the user's intention. However, propagating the user inputs to the rest of the images requires solving an enormous optimization problem, which is very time consuming, thus preventing its practical use. In this paper, a two-step edit propagation scheme is proposed, first to solve edits on clusters of similar pixels and then to interpolate individual pixel edits from cluster edits. The key in our scheme is that we use efficient stroke sampling to compute the affinity between image pixels and strokes. Based on this, our clustering does not need to be strokeadaptive and thus the number of clusters is greatly reduced, resulting in a significant speedup. The proposed method has been tested on various images, and the results show that it is more than one order of magnitude faster than existing methods, while still achieving precise results compared with the ground truth. Moreover, its efficiency is not sensitive to the number of strokes, making it suitable for performing dense edits in practice.
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    A Graph-based Approach to Continuous Line Illustrations with Variable Levels of Detail
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Wong, Fernando J.; Takahashi, Shigeo; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    This paper introduces a method for automatically generating continuous line illustrations, drawings consisting of a single line, from a given input image. Our approach begins by inferring a graph from a set of edges extracted from the image in question and obtaining a path that traverses through all edges of the said graph. The resulting path is then subjected to a series of post-processing operations to transform it into a continuous line drawing. Moreover, our approach allows us to manipulate the amount of detail portrayed in our line illustrations, which is particularly useful for simplifying the overall illustration while still retaining its most significant features. We also present several experimental results to demonstrate that our approach can automatically synthesize continuous line illustrations comparable to those of some contemporary artists.
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    An Illustrative Visualization Framework for 3D Vector Fields
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Chen, Cheng-Kai; Yan, Shi; Yu, Hongfeng; Max, Nelson; Ma, Kwan-Liu; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    Most 3D vector field visualization techniques suffer from the problem of visual clutter, and it remains a challenging task to effectively convey both directional and structural information of 3D vector fields. In this paper, we present a novel visualization framework that combines the advantages of clustering methods and illustrative rendering techniques to generate a concise and informative depiction of complex flow structures. Given a 3D vector field, we first generate a number of streamlines covering the important regions based on an entropy measurement. Then we decompose the streamlines into different groups based on a categorization of vector information, wherein the streamline pattern in each group is ensured to be coherent or nearly coherent. For each group, we select a set of representative streamlines and render them in an illustrative fashion to enhance depth cues and succinctly show local flow characteristics. The results demonstrate that our approach can generate a visualization that is relatively free of visual clutter while facilitating perception of salient information of complex vector fields.
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    Rephotography Using Image Collections
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Lee, Kun-Ting; Luo, Sheng-Jie; Chen, Bing-Yu; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    This paper proposes a novel system that 'rephotographs' a historical photograph with a collection of images. Rather than finding the accurate viewpoint of the historical photo, users only need to take a number of photographs around the target scene. We adopt the structure from motion technique to estimate the spatial relationship among these photographs, and construct a set of 3D point cloud. Based on the user-specified correspondences between the projected 3D point cloud and historical photograph, the camera parameters of the historical photograph are estimated. We then combine forward and backward warping images to render the result. Finally, inpainting and content-preserving warping are used to refine it, and the photograph at the same viewpoint of the historical one is produced by this photo collection.
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    SSD: Smooth Signed Distance Surface Reconstruction
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Calakli, Fatih; Taubin, Gabriel; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    We introduce a new variational formulation for the problem of reconstructing a watertight surface defined by an implicit equation, from a finite set of oriented points; a problem which has attracted a lot of attention for more than two decades. As in the Poisson Surface Reconstruction approach, discretizations of the continuous formulation reduce to the solution of sparse linear systems of equations. But rather than forcing the implicit function to approximate the indicator function of the volume bounded by the implicit surface, in our formulation the implicit function is forced to be a smooth approximation of the signed distance function to the surface. Since an indicator function is discontinuous, its gradient does not exist exactly where it needs to be compared with the normal vector data. The smooth signed distance has approximate unit slope in the neighborhood of the data points. As a result, the normal vector data can be incorporated directly into the energy function without implicit function smoothing. In addition, rather than first extending the oriented points to a vector field within the bounding volume, and then approximating the vector field by a gradient field in the least squares sense, here the vector field is constrained to be the gradient of the implicit function, and a single variational problem is solved directly in one step. The formulation allows for a number of different efficient discretizations, reduces to a finite least squares problem for all linearly parameterized families of functions, and does not require boundary conditions. The resulting algorithms are significantly simpler and easier to implement, and produce results of quality comparable with state-of-the-art algorithms. An efficient implementation based on a primal-graph octree-based hybrid finite element-finite difference discretization, and the Dual Marching Cubes isosurface extraction algorithm, is shown to produce high quality crack-free adaptive manifold polygon meshes.
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    RepSnapping: Efficient Image Cutout for Repeated Scene Elements
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Huang, Hua; Zhang, Lei; Zhang, Hong-Chao; Bing-Yu Chen, Jan Kautz, Tong-Yee Lee, and Ming C. Lin
    Repeated scene elements are copious and ubiquitous in natural images. Cutout of those repeated elements usually involves tedious and laborious user interaction by previous image segmentation methods. In this paper, we present RepSnapping, a novel method oriented to cutout of repeated scene elements with much less user interaction. By exploring inherent similarity between repeated elements, a new optimization model is introduced to thread correlated elements in the segmentation procedure. The model proposed here enables efficient solution using maxflow/ min cut on an extended graph. Experiments indicate that RepSnapping facilitates cutout of repeated elements better than the state-of-the-art interactive image segmentation and repetition detection methods.