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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： C.E. Scheidegger J.L.D. Comba R.D. da Cunha Instituto de Informática UFRGS Brazil

Modern programmable graphics hardware offers sufficient computing power to suggest the implementation of traditional algorithms on the graphics processor. this paper describes a complete implementation of a standard technique to solve the incompressible Navier-Stokes fluid equations running entirely on the GPU: the SMAC (simplified marker and cell) method. this method is widely used in engineering applications. the described implementation works with general rectangular domains, with or without obstacles, and with a variety of boundary conditions. Furthermore, we show that our implementation is about sixteen times faster than a reference CPU implementation running on similar cost hardware. Finally, we discuss simple extensions to the method to deal with more general situations, such as free boundary-value problems and three-dimensional domains.

关键词： Hardware computer graphics Navier-Stokes equations Central processing Unit Fluid dynamics Pipelines Computational modeling Power engineering computing Power engineering and energy Boundary conditions

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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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Towards 3D reconstruction of endoscope images using shape from shading

Towards 3D reconstruction of endoscope images using shape fr...

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： C.H. Quartucci Forster C.L. Tozzi Universidade Estadual de Campinas Campinas SP BR

the 3D reconstruction problem from a single endoscope image of a smooth object is studied in the context of the shape from shading methods and considering a single light source at the camera projection center. Based on a curve expansion shape from shading algorithm, a spherical projection model for the endoscope camera and a dichromatic model for the surface reflectance, an approach to solve practical problems, namely the endoscope image distortion and the removal of the image specular reflection component, is presented. Results obtained from application of this approach to synthetic and real images are presented.

关键词： image reconstruction Endoscopes Shape Cameras Light sources Surface reconstruction Reflectivity Optical reflection Data visualization Lenses

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image segmentation by tree pruning

Image segmentation by tree pruning

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： A.X. Falcao F.P.G. Bergo P.A.V. Miranda Institute of Computing State University of Campinas Sao Paulo Brazil

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 Pixel image processing image analysis Tree graphs Topology Geophysics computing Filtering Application software computer graphics

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image-based texture analysis for realistic image synthesis

Image-based texture analysis for realistic image synthesis

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： H. Mayer Computer Graphics and Vision Graz University of Technology Graz Austria

We present a method to measure reflectance and texture of surfaces in a one step process. For later use in digital image synthesis, it is mandatory to separate the gathered intensity values into these two parts to eliminate highlighting artifacts from textures. Our image based measurement system delivers bidirectional reflectance distribution function (BRDF) values distributed over the surface of the material under investigation. After fitting a reflectance model to the gathered data, we estimate the modulation of the diffuse reflectance coefficient which represents the texture. the last step analyzes the texture to get a parameterized and compact description of the measured surface properties. these results allow us to apply the gathered surface properties to objects with arbitrary shape and size. To keep the measurement system simple, a standard CCD camera and light source are used.

关键词： image analysis image texture analysis image generation Reflectivity Surface fitting Surface texture Digital images Bidirectional control Distribution functions Shape

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Improved FingerCode Matching Function

Improved FingerCode Matching Function

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： Gustavo de Sa Roberto Lotufo Sch. of Electr. & Comput. Eng. Campinas Univ. School of Electrical and Computer Engineering University of Campinas (UNICAMP) Campinas SP Brazil

FingerCode is a fingerprint correlation matching scheme that relies on texture information. In this scheme, the oriented components are extracted from a fingerprint image using a bank of Gabor filters, and a directional texture feature vector is computed for each oriented component. the feature vectors from the input and template images are compared and a matching score is obtained. Here, we explore ways to improve the matching score for the FingerCode method by using more complex matching functions. the best results were obtained by applying a nonlinear function to the texture values and weighting the texture vectors based on the spatial distribution

关键词： Fingerprint recognition Gabor filters image matching Fingers Pixel Data mining Filter bank Frequency Iris recognition Euclidean distance

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Expression Transfer between Photographs through Multilinear AAM's

Expression Transfer between Photographs through Multilinear ...

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： Ives Macedo Emilio Vital Brazil Luiz Velho IMPA-Instituto Nacional de Matemática Pura e Aplicada Brazil

Expression transfer is a method for mapping a photographed expression performed by a given subject onto the photograph of another person's face. Building on well succeeded previous works by the vision researchers (facial expression decomposition, active appearance models and multilinear analysis, we propose a novel approach for expression transfer based on color images. We attack this problem with methods developed by the computer vision community for facial expression analysis and recognition. Combining active appearance models and multilinear analysis, it's possible to suitably represent and analyze expressive facial images, while separating both style (subject's identity) and content (expressive flavor) from the captured performance

关键词： Active appearance model Tensile stress Facial animation image databases image analysis image color analysis Performance analysis Visual databases Face detection computer vision

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Visualization of Industrial Structures with Implicit GPU Primitives

Visualization of Industrial Structures with Implicit GPU Pri...

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4th International symposium on Visual Computing

作者： de Toledo, Rodrigo Levy, Bruno Petrobras - CENPES/PDP/GR Brazil INRIA - ALICE France

ISBN: (纸本)9783540896388

We present a method to interactively visualize large industrial models by replacing most triangles with implicit CPU primitives: cylinders;cone and torus slices. After a reverse-engineering process that recovers these primitives from triangle meshes;we encode their implicit parameters in a texture that is sent to the CPU. In rendering tune, the implicit primitives are visualized seamlessly with other triangles in the scene. the method was tested on two massive industrial models, achieving better performance and image quality while reducing memory use.

关键词： graphics processing unit

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A computer vision framework for eye gaze tracking

A computer vision framework for eye gaze tracking

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： M.R.M. Mimica C.H. Morimoto Departamento de Ciência da Computaç ão IME USP Sao Paulo Brazil

Eye gaze tracking (EGT) allows us to estimate the direction of gaze and the point of regard. this technique has been successfully used as a pointing device in computer interfaces for people with disabilities, but significant technological advances are still required to make EGT appropriate to be used in general computer interfaces. In order to improve the EGT technology, a testbed where new devices and algorithms can be evaluated must be defined. We present a survey of the methods used for EGT, and organize them into a computer vision framework, that we use to support the development and evaluation of new techniques. As an example of application of the framework, the calibration function used in the EGT developed in our laboratory is tested, and the results show the precision of the method. Higher accuracy of the testing results is achieved using synthetic images generated by ray tracing, from a physically based model of the eye.

关键词： computer vision computer interfaces Testing Human computer interaction Mice Costs Head image generation Ray tracing computer graphics

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A longest common subsequence approach to detect cut and wipe video transitions

A longest common subsequence approach to detect cut and wipe...

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brazilian symposium on computer graphics and image processing (SIBGRAPI)

作者： F.N. Bezerra Universidade de Fortaleza (Unifor) Fortaleza Brazil

We address in this work the problem of video transition detection, which is an important task in the video indexing and retrieval domain. the video slice is a single two-dimensional image that represents a video preserving information allowing the detection of different visual events in the original video. In particular it is possible to characterize shot transitions. We use the longest common subsequence (LCS) between two strings to transform the video slice into one-dimensional signals obtaining a highly simplified representation of the video content. Further we developed a chain of operations over these signals leading to the detection of cut and wipe transitions.

关键词： Layout Video sequences Indexing Gunshot detection systems Motion detection Detectors Pixel Histograms Event detection image segmentation

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