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17th brazilian symposium on computer graphics and image processing/2nd Ibero-American symposium on computer graphics

作者： Falcao, AX Bergo, FPG Miranda, PAV Univ Estadual Campinas Inst Comp BR-13084851 Campinas SP Brazil

ISBN: (纸本)0769522270

The image Foresting Transform (IFT) has been proposed for the design of image operators based on connectivity. The IFT reduces image processing problems into a minimum-cost path forest problem in a graph derived from the image. It has been successfully used for image filtering, segmentation, and analysis. In this work, we propose a novel image operator which solves segmentation by pruning trees of the forest. First, an IFT is applied to create an optimum-path forest whose roots are pixels selected inside a desired object. In this forest, the background consists of a few subtrees rooted at pixels on the object's boundary. These boundary pixels are identified and their subtrees are eliminated, such that the remaining forest defines the object. The tree pruning is an effective alternative to situations where image segmentation methods based on competing seeds fail. We present an interactive implementation of the tree-pruning technique, show several examples and discuss some experiments toward fully automatic segmentation.

关键词： image segmentation

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Loop snakes:: Snakes with enhanced topology control

Loop snakes:: Snakes with enhanced topology control

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17th brazilian symposium on computer graphics and image processing/2nd Ibero-American symposium on computer graphics

作者： Oliveira, A Ribeiro, S Farias, R Esperança, C Giraldi, G Univ Fed Rio de Janeiro COPPE Dept Syst Engn & Comp Sci Rio de Janeiro RJ Brazil

ISBN: (纸本)0769522270

Topologically adaptable snakes, or simply T-snakes, are a standard tool for automatically identifying multiple segments in an image. This work introduces a novel approach for controlling the topology of a T-snake. It focuses on the loops formed by the so-called projected curve which is obtained at every stage of the snake evolution. The idea is to make that curve the image of a piecewise linear mapping of an adequate class. Then, with the help of an additional structure-the Loop-Tree-it is possible to decide in O(1) time whether the region enclosed by each loop has already been explored by the snake. This makes it possible to construct an enhanced algorithm for evolving T-snakes whose performance is assessed by means of statistics and examples.

关键词： image segmentation

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New Higher-resolution Discrete Euclidean Medial Axis in nD with Linear Time Parallel Algorithm

New Higher-resolution Discrete Euclidean Medial Axis in <i>n...

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21st brazilian symposium on computer graphics and image processing

作者： Saude, Andre Vital Univ Fed Lavras Dept Comp Sci BR-37200000 Lavras MG Brazil

ISBN: (纸本)9780769533582

The notion of skeleton plays a major role in shape analysis since the introduction of the medial axis. The continuous medial axis is a skeleton with the following characteristics: centered, thin, homotopic, and reversible (sufficient for the reconstruction of the original object). The discrete Euclidean medial axis (MA) is also reversible and centered, but no longer homotopic nor thin. To preserve topology and reversibility, the MA is usually combined with homotopic thinning algorithms. Since there is a robust and well defined framework for fast homotopic thinning defined in the domain of abstract complexes, some authors have extended the MA to a doubled resolution grid and defined the discrete Euclidean Medial Axis in Higher Resolution (HMA), which can be combined to the framework defined on abstract complexes. Other authors gave an alternative definition of medial axis, which is a reversible subset of the MA, and is called Reduced Discrete Medial Axis (RDMA). The RDMA is thinner than the MA and can be computed in optimal time. In this paper we extend the RDMA to the doubled resolution grid and we define the High-resolution RDMA (HRDMA). The HRDMA is reversible and it can be computed in optimal time. The HRDMA can be combined with the algorithms in abstract complexes, so a reversible and homotopic Euclidean skeleton can be computed in optimal time.

关键词： medial axis skeleton Euclidean distance shape representation

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Interactive editing of multiresolution meshes

Interactive editing of multiresolution meshes

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17th brazilian symposium on computer graphics and image processing/2nd Ibero-American symposium on computer graphics

作者： Silva, FGM Gomes, AJP Univ Beira Interior Dept Comp Sci & Engn IT Networks & Multimedia Grp Covilha Portugal

ISBN: (纸本)0769522270

This paper presents a new approach for interactive editing of multiresolution meshes. Editing operations (e.g. scaling and rotation) are confined to mesh regions of interest, called sub-meshes. Also, intuitive deformation operations (e.g. tapering and twisting) as required for animation systems can be used as well, allowing the user to have control on the local deformations of mesh objects. For that, each sub-mesh is defined interactively by picking up the cells of its frontier. Alternatively, a sub-mesh can be delimited by the shortest path of edges that approximates the intersection between a mesh and a given cutting plane. In order to speed up editing operations, the mesh is first simplified, the target sub-mesh is edited, and finally the whole mesh is refined back to its original resolution. This is particularly important for large meshes.

关键词： Interactive computer graphics

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Curvature dependent polygonization of implicit surfaces

Curvature dependent polygonization of implicit surfaces

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17th brazilian symposium on computer graphics and image processing/2nd Ibero-American symposium on computer graphics

作者： de Araújo, BR Jorge, JAP Univ Tecn Lisboa IST INESCID Dept Informat Syst & Comp Engn P-100029 Lisbon Portugal

ISBN: (纸本)0769522270

We present an algorithm for polygonizing closed implicit surfaces, which produces meshes adapted to the local curvature of the surface. Our method is similar to, but NOT based on, Marching Triangles, in that we start from a point on the surface and develop a mesh from that point using a surface-tracking approach. In a marked departure from previous approaches, our meshes approximate the surface through heuristics relying on curvature. Furthermore, our method works completely on-the-fly, resolving cracks as it proceeds, without the need for any post-remeshing step to correct failures. We have tested the algorithm with three different representations of implicit surfaces, Variational, analythical and MP U, using non-trivial data sets, yielding results that illustrate the flexibility and scalability of our technique. Performance comparisons with variants of Marching Cubes show that our approach is capable of good accuracy and meshing quality without sacrificing computing resources.

关键词： computer graphics

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Hierarchy-of-Visual-Words: a Learning-based Approach for Trademark image Retrieval 32

Hierarchy-of-Visual-Words: a Learning-based Approach for Tra...

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32nd SIBGRAPI Conference on graphics, Patterns and images (SIBGRAPI) / symposium on Virtual and Augmented Reality (SVR)

作者： Lourenco, Vitor N. Silva, Gabriela G. Fernandes, Leandro A. F. Univ Fed Fluminense Inst Computacao Niteroi RJ Brazil

ISBN: (纸本)9781728152271

In this paper, we present the Hierarchy-of-Visual-Words (HoVW), a novel trademark image retrieval (TIR) method that decomposes images into simpler geometric shapes and defines a descriptor for binary trademark image representation by encoding the hierarchical arrangement of component shapes. The proposed hierarchical organization of visual data stores each component shape as a visual word. It is capable of representing the geometry of individual elements and the topology of the trademark image, making the descriptor robust against linear as well as to some level of nonlinear transformation. Experiments show that HoVW outperforms previous TIR methods on the MPEG-7 CE-1 and MPEG-7 CE-2 image databases.

关键词： Machine Learning Trademark image Retrieval Visual feature extraction and matching

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Denoising and enhancing digital mammographic images for visual screening

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computerIZED MEDICAL IMAGING And graphics 2006年第4期30卷 243-254页

作者： Scharcanski, Jacob Jung, Claudio Rosito Univ Fed Rio Grande do Sul BR-91501970 Porto Alegre RS Brazil Univ Vale Rio dos Sinos PIPCA Grad Sch Appl Comp UNISINOS BR-93022000 Sao Leopoldo RS Brazil

Dense regions in digital mammographic images are usually noisy and have low contrast, and their visual screening is difficult. This paper describes a new method for mammographic image noise suppression and enhancement, which can be effective particularly for screening image dense regions. Initially, the image is preprocessed to improve its local contrast and the discrimination of subtle details. Next, image noise suppression and edge enhancement are performed based on the wavelet transform. At each resolution, coefficients associated with noise are modelled by Gaussian random variables;coefficients associated with edges are modelled by Generalized Laplacian random variables, and a shrinkage function is assembled based on posterior probabilities. The shrinkage functions at consecutive scales are combined, and then applied to the wavelets coefficients. Given a resolution of analysis, the image denoising process is adaptive (i.e. does not require further parameter adjustments), and the selection of a gain factor provides the desired detail enhancement. The enhancement function was designed to avoid introducing artifacts in the enhancement process, which is essential in mammographic image analysis. Our preliminary results indicate that our method allows to enhance local contrast, and detect microcalcifications and other suspicious structures in situations where their detection would be difficult otherwise. Compared to other approaches, our method requires less parameter adjustments by the user. (c) 2006 Elsevier Ltd. All rights reserved.

关键词： mammography contrast equalization image denoising image enhancement multiresolution analysis wavelets

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Digital visual information processing: Adding vision and graphics 1

Digital visual information processing: Adding vision and gra...

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1st International Workshop on image and Signal processing and Analysis (IWISPA 2000) in conjunction with the 22nd International Conf on Informat Technol Interfaces

作者： Leberl, FW Graz Tech Univ Inst Comp Graph & Vis A-8010 Graz Austria

ISBN: (纸本)9539676924

Models of the real world are at least 3-dimensional and require the technologies of image processing and computer graphics, We see the processing of images, be they of the real world or of models in a computer, as one and the same basic technology, namely "digital visual information processing". This paper seeks to illustrate and justify this point-of-view by means of examples taken mostly from the work at the author's institute.

关键词： image processing

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Level lines continuation based digital inpainting

Level lines continuation based digital inpainting

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17th brazilian symposium on computer graphics and image processing/2nd Ibero-American symposium on computer graphics

作者： Barcelos, CAZ Batista, MA Martins, AM Nogueira, AC Universidade Federal de Goiás CAC Univ. Federal de Uberlândia Brazil Univ. Federal de Uberlândia 38.400-902 Uberlândia MG CX.P. 593 Brazil

ISBN: (纸本)0769522270

Inpainting digital models have been since the late 1990's a powerful image reconstruction tool for missing data. After the original work of Bertalmio, Sapiro, Caselles and Ballester [1] several different approaches have been used to tackle the problem. Some are based on Partial Differential Equations to model a transport process and a diffusion process, others are based on the Eider elastica functional. This paper presents a model using the level lines continuation to perform the filling-in of the inpainting domain D. The model is proposed in a way as to satisfy the "Connectivity Principle". The image u(x,y) is represented by a family of level lines and the missing part Of the image is filled-in by the propagation of the available surrounding information, from outside to inside of the inpainting domain D along the level lines of the image. After defining the domain D the restoration process becomes automatic and the final result u(x, y, t(n)) is carried out by the evolutionary process starting with the initial degraded image u(x, y, 0). Examples on real and textured images show the performance of this proposed model.

关键词： image reconstruction

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Exploring Double Cross Cyclic Interpolation in Unpaired image-to-image Translation 32

Exploring Double Cross Cyclic Interpolation in Unpaired Imag...

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32nd SIBGRAPI Conference on graphics, Patterns and images (SIBGRAPI) / symposium on Virtual and Augmented Reality (SVR)

作者： Lopez, Jorge Mauricio, Antoni Camara, Guillermo Univ Catolica San Pablo Dept Comp Sci Arequipa Peru Univ Fed Ouro Preto Dept Comp Sci Ouro Preto MG Brazil

ISBN: (纸本)9781728152271

The unpaired image-to-image translation consists of transferring a sample a in the domain A to an analog sample b in the domain B without intensive pixel-to-pixel supervision. The current vision focuses on learning a generative function that maps both domains but ignoring the latent information, although its exploration is not explicit supervision. This paper proposes a cross-domain GAN-based model to achieve a bi-directional translation guided by latent space supervision. The proposed architecture provides a double-loop cyclic reconstruction loss in an exchangeable training adopted to reduce mode collapse and enhance local details. Our proposal has outstanding results in visual quality, stability, and pixel-level segmentation metrics over different public datasets.

关键词： Cross domain interpolation Latent space exploration Unpaired image to image Translation

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