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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： L. Velho J. Gomes IMPA-Instituto de Matemática Pura e Aplicada Brazil

We introduce variable resolution 4-k meshes, a powerful structure for the representation of geometric objects at multiple levels of detail. It combines most properties of other related descriptions with several advantages, such as more flexibility and greater expressive power. the main unique feature of the 4-k mesh structure lies in its variable resolution capability, which is crucial for adaptive computation. We also give an overview of the different methods for constructing the hierarchical 4-k mesh representation, as well as the basic algorithms necessary to incorporate it in modeling and graphics applications.

关键词： Humans Application software Solid modeling computer graphics Visualization

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A new method for static video summarization using local descriptors and video temporal segmentation

A new method for static video summarization using local desc...

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2013 26th Conference on graphics, Patterns and images, SIBGRAPI 2013

作者： Cahuina, Edward J.Y. Cayllahua Chavez, Guillermo Camara Computer Research Center San Pablo Catholic University Arequipa Peru Department of Computer Science Federal University of Ouro Preto Ouro Preto Brazil

ISBN: (纸本)9780769550992

the continuous creation of digital video has caused an exponential growth of digital video content. To increase the usability of such large volume of videos, a lot of research has been made. Video summarization has been proposed to rapidly browse large video collections. To summarize any type of video, researchers have relied on visual features contained in frames. In order to extract these features, different techniques have used local or global descriptors. In this paper, we propose a method for static video summarization that can produce meaningful and informative video summaries. We perform an evaluation using over 100 videos in order to achieve a stronger position about the performance of local descriptors in semantic video summarization. Our experimental results show, with a confidence level of 99%, that our proposed method using local descriptors and temporal video segmentation produces better summaries than state of the art methods. We also demonstrate the importance of a more elaborate method for temporal video segmentation, improving the generation of summaries, achieving 10% improvement in accuracy. We also acknowledge a marginal importance of color information when using local descriptors to produce video summaries. © 2013 IEEE.

关键词： Semantics

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A project for hand gesture recognition

A project for hand gesture recognition

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： C.R.P. Dionisio R.M. Cesar Department of Computer Science University of Sao Paulo Sao Paulo Brazil

this paper discusses an ongoing project for hand gesture recognition in computer vision systems. the proposed approach is based on the shape analysis tools introduced by R.M. Cesar Jr. and L. da F. Costa (1997). More specifically, the wavelet transform is used to generate features for the recognition of hand gestures based on contours.

关键词： Algorithm design and analysis Continuous wavelet transforms Shape Wavelet transforms image analysis Feature extraction computer science computer vision Man machine systems Deafness

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Improving image classification through descriptor combination

Improving image classification through descriptor combinatio...

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25th Conference on graphics, Patterns and images, SIBGRAPI 2012

作者： Mansano, A. Matsuoka, J.A. Afonso, L.C.S. Papa, J.P. Faria, F. Da S. Torres, R. Department of Computing São Paulo State University Bauru Brazil Institute of Computing University of Campinas Campinas SP Brazil

ISBN: (纸本)9780769548296

the efficiency in image classification tasks can be improved using combined information provided by several sources, such as shape, color, and texture visual properties. Although many works proposed to combine different feature vectors, we model the descriptor combination as an optimization problem to be addressed by evolutionary-based techniques, which compute distances between samples that maximize their separability in the feature space. the robustness of the proposed technique is assessed by the Optimum-Path Forest classifier. Experiments showed that the proposed methodology can outperform individual information provided by single descriptors in well-known public datasets. © 2012 IEEE.

关键词： image classification

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GPU-Based Cell Projection for Interactive Volume Rendering

GPU-Based Cell Projection for Interactive Volume Rendering

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： Ricardo Marroquim Andre Maximo Ricardo Farias Claudio Esperanca Universidade Federal do Rio de Janeiro Brazil

We present a practical approach for implementing the projected tetrahedra (PT) algorithm for interactive volume rendering of unstructured data using programmable graphics cards. Unlike similar works reported earlier, our method employs two fragment shaders, one for computing the tetrahedra projections and another for rendering the elements. We achieve interactive rates by storing the model in texture memory and avoiding redundant projections of implementations using vertex shaders. Our algorithm is capable of rendering over 2.0 M Tet/s on current graphics hardware, making it competitive with recent ray-casting approaches, while occupying a substantially smaller memory footprint

关键词： Transfer functions Hardware Rendering (computer graphics) Projection algorithms computer graphics Nonlinear optics Optical attenuators Linear approximation Software algorithms Biomedical imaging

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A load-balancing strategy for sort-first distributed rendering

A load-balancing strategy for sort-first distributed renderi...

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： F. Abraham W. Celes R. Cerqueira J.L. Campos Tecgraf-Computer Science Department PUC-Rio Rio de Janeiro Rio de Janeiro Brazil

In this paper we present a multi-threaded sort-first distributed rendering system. In order to achieve load balance among the rendering nodes, we propose a new partitioning scheme based on the rendering time of the previous frame. the proposed load-balancing algorithm is very simple to be implemented and works well for both geometry and rasterization-bound models. We also propose a strategy to assign tiles to rendering nodes that effectively uses the available graphics resources, thus improving rendering performance.

关键词： Rendering (computer graphics) graphics Layout Tiles Partitioning algorithms Workstations Delay Clustering algorithms Personal communication networks Displays

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Object segmentation in image sequences by watershed from markers: a generic approach

Object segmentation in image sequences by watershed from mar...

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： F.C. Flores R. de Alencar Lotufo Faculdade de Engenharia Elétrica e de Computaç ão State University of Campinas-UNICAMP Brazil Departamento de Informática UEM Brazil

We propose a generic method to interactive object segmentation in image sequences. this method consists in the extension of efficient techniques of static image segmentation to image sequences by combining them to fast motion estimation techniques. the proposed method has the following characteristics: interactivity, generality, rapid response and progressive manual edition.

关键词： Object segmentation image sequences image segmentation Motion estimation Biomedical imaging Tracking Video coding MPEG 4 Standard Video surveillance Object detection

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On the Salience of Adversarial Examples 14th

On the Salience of Adversarial Examples

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14th International symposium on Visual Computing (ISVC)

作者： Fernandez, Amanda Univ Texas San Antonio Dept Comp Sci San Antonio TX 78249 USA

ISBN: (纸本)9783030337230;9783030337223

Adversarial examples are beginning to evolve as rapidly as the deep learning models they are designed to attack. these intentionally-manipulated inputs attempt to mislead the targeted model while maintaining the appearance of innocuous input data. Countermeasures against these attacks that take a global approach tend to be lossy to the original data, or ineffective in removing the perturbations. Localized approaches have proven effective, however it is difficult to identify affected areas in the data in order to apply a targeted cleaning algorithm. For image data, visual saliency estimation models identify important features in an image, and provide a targeting mechanism for countering adversarial examples. In this work, we examine the effectiveness of state-of-the-art saliency models on complex scenes, in their original and perturbed forms. In a thorough range of standard metrics, we compare performance on clean image data with adversarial examples to demonstrate the vulnerability of deep learning-based saliency models to adversarial examples.

关键词： Adversarial examples Visual saliency image processing Deep learning

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Mumford-Shah on the move: Region-based segmentation on deforming manifolds with application to 3-D reconstruction of shape and appearance from multi-view images

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JOURNAL OF MAthEMATICAL IMAGING AND VISION 2007年第2-3期29卷 219-234页

作者： Jin, Hailin Yezzi, Anthony J. Soatto, Stefano Adobe Syst Inc Off Tech San Jose CA 95110 USA Georgia Inst Technol Sch Elect & Comp Engn Atlanta GA 30332 USA Univ Calif Los Angeles Dept Comp Sci Los Angeles CA 90025 USA

We address the problem of estimating the shape and appearance of a scene made of smooth Lambertian surfaces with piecewise smooth albedo. We allow the scene to have self-occlusions and multiple connected components. this class of surfaces is often used as an approximation of scenes populated by man-made objects. We assume we are given a number of images taken from different vantage points. Mathematically this problem can be posed as an extension of Mumford and Shah's approach to static image segmentation to the segmentation of a function defined on a deforming surface. We propose an iterative procedure to minimize a global cost functional that combines geometric priors on both the shape of the scene and the boundary between smooth albedo regions. We carry out the numerical implementation in the level set framework.

关键词： variational methods Mumford-Shah functional image segmentation multi-view stereo level set methods curve evolution on surfaces dense shape reconstruction structure from motion visibility

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Robust adaptive meshes for implicit surfaces

Robust adaptive meshes for implicit surfaces

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： Afonso Paiva Helio Lopes thomas Lewiner Luiz Henrique De Figueiredo Department of Mathematics PUC-Rio Brazil IMPA Rio de Janeiro Brazil

this work introduces a robust algorithm for computing good polygonal approximations of implicit surfaces, where robustness entails recovering the exact topology of the implicit surface. Furthermore, the approximate triangle mesh adapts to the geometry and to the topology of the real implicit surface. this method generates an octree subdivided according to the interval evaluation of the implicit function in order to guarantee the robustness, and to the interval automatic differentiation in order to adapt the octree to the geometry of the implicit surface. the triangle mesh is then generated from that octree through an enhanced dual marching

关键词： Robustness Topology Geometry Solid modeling Arithmetic Surface cracks Mathematics Isosurfaces Mesh generation Rendering (computer graphics)

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