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pacific conference on computer graphics and applications

作者： B. Kronrod C. Gotsman Computer Science Department Technion-Israel Institute of Technology Haifa Israel

Recently, a wealth of algorithms for the efficient coding of 3D triangle meshes have been published. All these focus on achieving the most compact code for the connectivity data. The geometric data, i.e. the vertex coordinates, are then coded in an order induced by the connectivity code, which is probably not optimal. This is a pity, as the geometric portion of the data set dominates the code. We propose a way to optimize the geometry code without sacrificing too much in the connectivity code. In our approach, we achieve approximately two bits/triangle for the connectivity before entropy coding, which is not as good as other published algorithms but certainly not significantly worse. Our approach is based on the parallelogram prediction method for mesh geometry. This method is based on the observation that two adjacent triangles in a typical mesh tend to form a shape similar to a parallelogram. If an algorithm uses a parallelogram prediction method then it should build a traversal structure of triangles covering all vertices. The vertex coordinates are then predicted as the structure is traversed. The cost of this code is then the entropy of the distribution of the vertex prediction errors. Since this entropy is hard to manipulate, the accepted practice is to measure the code's effectiveness in the approximation sense, i.e. as the sum of the lengths of the vertex prediction error vectors. The full version of this paper is available at .

关键词： Costs Geometry Tree graphs Prediction methods Decoding computer science Entropy coding Shape Length measurement Design optimization

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Secret video sharing

Secret video sharing

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作者： Alharthi, Saeed Atrey, Pradeep K. Kankanhalli, Mohan S. University of Winnipeg 515 Portage Avenue Winnipeg MB Canada School of Computing National University Singapore Singapore

Today digital videos are increasingly being used in many sensitive as well as commercial applications such as military secrets and corporate product designs. The secure sharing of these videos is of utmost importance. Traditional encryption methods do not guarantee perfect security and the secret can be revealed just by obtaining the decryption key. On the other hand, Shamir's secret sharing scheme has been widely used for secret image sharing, however it has never been explored for secret video sharing. In this paper, we present a method to share a video using Shamir's secret sharing scheme. The proposed method utilizes the temporal redundancy in videos and is computationally efficient. Experimental results show the utility of the proposed method.

关键词： computer graphics

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Automatic animation skeleton using repulsive force field

Automatic animation skeleton using repulsive force field

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pacific conference on computer graphics and applications

作者： Pin-Chou Liu Fu-Che Wu Wan-Chun Ma Rung-Huei Liang Ming Ouhyoung Communication and Multimedia Laboratory Department of Computer Science and Information Engineering National Taiwan University Taiwan

ISBN: (纸本)0769520286

A method is proposed in this paper to automatically generate the animation skeleton of a model such that the model can be manipulated according to the skeleton. With our method, users can construct the skeleton in a short time, and bring a static model both dynamic and alive. The primary steps of our method are finding skeleton joints, connecting the joints to form an animation skeleton, and binding skin vertices to the skeleton. Initially, a repulsive force field is constructed inside a given model, and a set of points with local minimal force magnitude are found based on the force field. Then, a modified thinning algorithm is applied to generate an initial skeleton, which is further refined to become the final result. When the skeleton construction completes, skin vertices are anchored to the skeleton joints according to the distances between the vertices and joints. In order to build the repulsive force field, hundreds of rays are shot radially from positions inside the model, and it leads to that the force field computation takes most of the execution time. Therefore, an octree structure is used to accelerate this process. Currently, the skeleton generated from a typical 3D model with 1000 to 10000 polygons takes less than 2 minutes on a Intel Pentium 4 2.4 GHz PC.

关键词： Animation Skeleton Joints Skin computer graphics Packaging Multimedia communication Laboratories computer science Joining processes

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Laplacian Guided Editing, Synthesis, and Simulation

Laplacian Guided Editing, Synthesis, and Simulation

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pacific conference on computer graphics and applications

作者： Dr. Yizhou Yu University of Illinois Urbana-Champaign USA

Summary form only given. The Laplacian has been playing a central role in numerous scientific and engineering problems. It has also become popular in computer graphics. This talk presents a series of our work that exploits the Laplacian in mesh editing, texture synthesis and flow simulation. First, a review is given on mesh editing using differential coordinates and the Poisson equation, which involves the Laplacian. The distinctive feature of this approach is that it modifies the original geometry implicitly through gradient field manipulation. This approach can produce desired results for both global and local editing operations, such as deformation, object merging, and denoising. This technique is computationally involved since it requires solving a large sparse linear system. To overcome this difficulty, an efficient multigrid algorithm specifically tailored for geometry processing has been developed. This multigrid algorithm is capable of interactively processing meshes with hundreds of thousands of vertices. In our latest work, Laplacian-based editing has been generalized to deforming mesh sequences, and efficient user interaction techniques have also been designed. Second, this talk presents a Laplacian-based method for surface texture synthesis and mixing from multiple sources. Eliminating seams among texture patches is important during texture synthesis. In our technique, it is solved by performing Laplacian texture reconstruction, which retains the high frequency details but computes new consistent low frequency components. Third, a method for inviscid flow simulation over manifold surfaces is presented. This method enforces incompressibility on closed surfaces by solving a discrete Poisson equation. Different from previous work, it performs simulations directly on triangle meshes and thus eliminates parametrization distortions.

关键词： Laplace equations Computational modeling Surface reconstruction Poisson equations Geometry Frequency computer graphics Merging Noise reduction Linear systems

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Automatic creation of object hierarchies for radiosity clustering

Automatic creation of object hierarchies for radiosity clust...

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pacific conference on computer graphics and applications

作者： G. Muller S. Schafer D.W. Fellner Technische Universitat Braunschweig Braunschweig Niedersachsen DE Institute of Computer Graphics Technical University of Braunschweig Brunswick Germany

Using object clusters for hierarchical radiosity greatly improves the efficiency and thus usability of radiosity computations. By eliminating the quadratic starting phase very large scenes containing about 100 K polygons can be handled efficiently. Although the main algorithm extends rather easily to using object clusters, the creation of "good" object hierarchies is a difficult task both in terms of construction time and in the way how surfaces or objects are grouped to clusters. The quality of an object hierarchy for clustering depends on its ability to accurately simulate the hierarchy of the energy flow in a given scene. Additionally it should support visibility computations by providing efficient ray acceleration techniques. In this paper we present a new approach of building hierarchies of object clusters. Our hybrid structuring algorithm provides accuracy and speed by combining a highly optimized bounding volume hierarchy together with uniform spatial subdivisions for nodes with regular object densities. The algorithm works without user intervention and is well suited for a wide variety of scenes. First results of using these hierarchies in a radiosity clustering environment are very promising and will be presented here. The combination of very deep hierarchies (we use a binary tree) together with an efficient ray acceleration structure shifts the computational effort away from form factor and visibility calculation towards accurately propagating the energy through the hierarchy. We show how an efficient single pass gathering can be used to minimize traversal costs.

关键词： Clustering algorithms Layout Costs computer graphics Buildings Energy exchange Reflection Algorithm design and analysis Computational modeling Casting

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L0 Gradient-Preserving Color Transfer

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computer graphics FORUM 2017年第7期36卷 93-103页

作者： Wang, Dong Zou, Changqing Li, Guiqing Gao, Chengying Su, Zhuo Tan, Ping South China Agr Univ Coll Math & Informat Guangzhou Guangdong Peoples R China Hengyang Normal Univ Coll Comp Sci & Technol Hengyang Peoples R China Simon Fraser Univ Sch Comp Sci Burnaby BC Canada South China Univ Technol Sch Comp Sci & Engn Guangzhou Guangdong Peoples R China Sun Yat Sen Univ Natl Engn Res Ctr Digital Life Sch Data & Comp Sci Guangzhou Guangdong Peoples R China

This paper presents a new two-step color transfer method which includes color mapping and detail preservation. To map source colors to target colors, which are from an image or palette, the proposed similarity-preserving color mapping algorithm uses the similarities between pixel color and dominant colors as existing algorithms and emphasizes the similarities between source image pixel colors. Detail preservation is performed by an L0 gradient-preserving algorithm. It relaxes the large gradients of the sparse pixels along color region boundaries and preserves the small gradients of pixels within color regions. The proposed method preserves source image color similarity and image details well. Extensive experiments demonstrate that the proposed approach has achieved a state-of-art visual performance.

关键词： CCS Concepts computer graphics → Image & Video Image/Video Editing

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Genus Oblivious Cross Parameterization: Robust Topological Management of Inter-Surface Maps

Genus Oblivious Cross Parameterization: Robust Topological M...

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pacific conference on computer graphics and applications

作者： Janine Bennett Valerio Pascucci Kenneth Joy Lawrence Livemore National Laboratory USA University of California Davis USA

We consider the problem of generating a map between two triangulated meshes, M and M', with arbitrary and possibly differing genus. This problem has rarely been tackled in its generality. Early schemes considered only topological spheres. Recent algorithms allow inputs with an arbitrary number of tunnels but require M and M' to have equal genus, mapping tunnel to tunnel. Other schemes which allow more general inputs are not guaranteed to work and the authors do not provide a characterization of the input meshes that can be processed successfully. Moreover, the techniques have difficulty dealing with coarse meshes with many tunnels. In this paper we present the first robust approach to build a map between two meshes of arbitrary unequal genus. We also provide a simplified method for setting the initial alignment between M and M', reducing reliance on landmarks and allowing the user to select "landmark tunnels" in addition to the standard landmark vertices. After computing the map, we automatically derive a continuous deformation from M to M' using a variational implicit approach to describe the evolution of non-landmark tunnels. Overall, we achieve a cross parameterization scheme that is provably robust in the sense that it can mapM toM' without constraints on their relative genus or on the density of the triangulation with respect to the number of tunnels. To demonstrate the practical effectiveness of our scheme we provide a number of examples of inter-surface parameterizations between meshes of different genus and shape.

关键词： Robustness Mesh generation Topology Shape Geometry computer graphics Application software conference management Laboratories Skeleton

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Visibility in the presence of occluders with curved boundaries

Visibility in the presence of occluders with curved boundari...

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pacific conference on computer graphics and applications

作者： G. Baciu C. Cheung Chun Yu Computer Science Department Hong Kong University of Science and Technology Hong Kong China

ISBN: (纸本)0769508685

Accurate global visibility information has become essential in global illumination rendering. Combinatorial structures, such as the visibility complex, aspect graphs and the visibility skeleton, are the seeds of a new topic of research motivated by practical problems in computer graphics and global illumination rendering. This is now attracting interest from the computational geometry, combinatorics, CAD and robotics communities. The initial motivation has been to accurately represent shadow boundaries generated by occluding surfaces in the path of light from emitting surfaces (sources) to receiving surfaces (receivers). This article adds to the rich body of research in this field by presenting solutions to the problem of occluders with curved boundaries. This has profound implications in three main areas: (1) the generation, maintenance and search functions associated with the global visibility complex, (2) mesh generation, and (3) global illumination rendering. We present a new visibility complex based on the proposed visibility skeleton. The new visibility complex has been designed to handle not only polygonal elements but also surfaces with curved boundaries. We have found that, even in simple 3D scenes, the new visibility complex generates less polygons in the meshing phase and a more accurate global illumination.

关键词： Lighting Rendering (computer graphics) Skeleton Mesh generation Layout computer graphics Computational geometry Combinatorial mathematics Robots Image generation

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Surface reconstruction with volume preservation

Surface reconstruction with volume preservation

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pacific conference on computer graphics and applications

作者： K. Aoki H. Yokota T. Kaneko Department of Information and Computer Sciences Toyohashi University of Technology Toyohashi Aichi Japan

The marching cubes (MC) algorithm is widely used for converting volume data into surface data. It generates surfaces with the connected intersection points with a level or value equal to a given threshold. The resulting surfaces are iso-surfaces. However, it will be shown that local volume is not preserved in the conversion. Consequently, the resulting shape is not necessarily close to the original shape. We present a new approach to the problem. Instead of a single threshold value for the entire image we adjust thresholds locally so that local volume becomes approximately equal to the corresponding voxel value. First, a detailed explanation is given using a 2D image. Then, for a 3D case a technique to analytically compute volume in various cases of forming iso-surfaces is developed. We will demonstrate the advantage of our algorithm using several artificial and real examples.

关键词： Surface reconstruction Shape Pixel Instruments Image reconstruction Image converters Biomedical imaging Computed tomography Magnetic resonance imaging Character generation

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Rate-Distortion Optimized Progressive 3D Reconstruction from Multi-view Images

Rate-Distortion Optimized Progressive 3D Reconstruction from...

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pacific conference on computer graphics and applications

作者： Viet Nam Nghiem Jianfei Cai Jianmin Zheng School of Computer Engineering Nanyang Technological University Singapore

Most of the previous multi-view reconstruction algorithms focus on minimizing reconstruction distortion, i.e. reconstructing a 3D model as close to the real object as possible, and rely on subsequent simplification process to control the reconstruction rate for practical usage. In this paper, in addition to reconstruction distortion, we directly consider the reconstruction rate in wide-baseline multi-view reconstruction. In particular, we develop a novel rate-distortion efficient multi-view reconstruction system, which consists of two major components: the PDE-based mesh optimization and the local subdivision based mesh refinement. Although both components are prior arts, to achieve rate-distortion optimization, new ingredients are proposed including non-uniform sample distribution for efficient and accurate surface distortion approximation in mesh optimization and non-uniform vertex distribution in mesh refinement. From a set of calibrated and segmented wide baseline images, our developed system is able to reconstruct the optimal 3D mesh that achieves minimum reconstruction distortion at any rate within a certain range. Experimental results show that our proposed system significantly outperforms the original PDE-based reconstruction method in both rate-distortion performance and visual quality.

关键词： Image reconstruction Surface reconstruction Three dimensional displays Optimization Distortion measurement Image resolution Surface treatment

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