By Topic

Graphics, Patterns and Images (Sibgrapi), 2011 24th SIBGRAPI Conference on

Date 28-31 Aug. 2011

Filter Results

Displaying Results 1 - 25 of 60
  • [Front cover]

    Page(s): C1
    Save to Project icon | Request Permissions | PDF file iconPDF (10535 KB)  
    Freely Available from IEEE
  • [Title page i]

    Page(s): i
    Save to Project icon | Request Permissions | PDF file iconPDF (43 KB)  
    Freely Available from IEEE
  • [Title page iii]

    Page(s): iii
    Save to Project icon | Request Permissions | PDF file iconPDF (81 KB)  
    Freely Available from IEEE
  • [Copyright notice]

    Page(s): iv
    Save to Project icon | Request Permissions | PDF file iconPDF (109 KB)  
    Freely Available from IEEE
  • Table of contents

    Page(s): v - ix
    Save to Project icon | Request Permissions | PDF file iconPDF (138 KB)  
    Freely Available from IEEE
  • Message from General Chairs

    Page(s): x
    Save to Project icon | Request Permissions | PDF file iconPDF (35 KB)  
    Freely Available from IEEE
  • Message from Program Chairs

    Page(s): xi
    Save to Project icon | Request Permissions | PDF file iconPDF (36 KB)  
    Freely Available from IEEE
  • Organizing Committee

    Page(s): xii
    Save to Project icon | Request Permissions | PDF file iconPDF (30 KB)  
    Freely Available from IEEE
  • Program Committee

    Page(s): xiii - xvi
    Save to Project icon | Request Permissions | PDF file iconPDF (39 KB)  
    Freely Available from IEEE
  • Reviewers

    Page(s): xvii - xx
    Save to Project icon | Request Permissions | PDF file iconPDF (39 KB)  
    Freely Available from IEEE
  • Sponsors/Conference Support

    Page(s): xxi
    Save to Project icon | Request Permissions | PDF file iconPDF (27 KB)  
    Freely Available from IEEE
  • Best Paper awards

    Page(s): xxii - xxiii
    Save to Project icon | Request Permissions | PDF file iconPDF (115 KB)  
    Freely Available from IEEE
  • Texturing 3D Models with Low Geometric Features

    Page(s): 1 - 8
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (706 KB) |  | HTML iconHTML  

    This paper presents a texture projection and alignment method specifically tailored for objects with low geometric features. A common way to build virtual replicas is to acquire the geometry with a 3D scanner and model its reflectance properties (i.e. colors) by projecting photos onto the 3D surface. To correctly align each photo it is necessary to retrieve the camera's extrinsic matrix, which is usually achieved by optimization algorithms that match geometric features of the model with their corresponding ones on the photos. However, when dealing with cultural heritage artifacts or mechanical pieces, for example, some models inherently lack significant geometric detail. We propose a method to automatically extract these features from high resolution photos and register them in a sequential manner using a variation of the contour-based approaches. The algorithm requires minimum user intervention as only an initial guess of the camera's direction is required for each photo. In addition, we describe an improved formulation of the optimization method based on a smooth function that avoids typical local minima found in this scenario. The results are illustrated with high-resolution textured models produced by our system. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Colorization and Illumination of 2D Animations Based on a Region-Tree Representation

    Page(s): 9 - 16
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1409 KB) |  | HTML iconHTML  

    Colorization and illumination are key processes for creating animated cartoons. Computer assisted methods have been incorporated in animation/illustration systems to reduce the artists' effort. This paper presents a new strategy for illumination and colorization of 2D drawings based on a region-tree. Starting from a hand-drawn cartoon, it extracts geometric and topological information and builds a tree structure, ensuring independence among parts of the drawing, such as curves and regions. Based on this structure and its attributes, a colorization method that propagates through consecutive frames of animation is proposed, together with an interpolation method that accurately computes a normal mapping for the illumination process. Different operators on curve and region attributes can be applied independently, obtaining different rendering effects. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A New Method for Cutting Splats of Models with Sharp Features

    Page(s): 17 - 24
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1254 KB) |  | HTML iconHTML  

    Surface splatting is a fast rendering technique for point-based models that usually delivers good-quality renderings. However, the intrinsic characteristic of this technique is the treatment of points as if they were discs. That requires special processing near sharp edges and corners in order to prevent rendering artifacts from appearing. In this work, we present a clever way of clipping splats near sharp edges and corners by a classification of neighboring splats, which belong to distinct intersecting surfaces. Those neighboring splats that take part in the clipping process are called clip partners. Their concavity or convexity with respect to one another are determined, as well as their relation with the clipped splat. In our approach, there is no need of distance computations nor of other complex operations during the rendering process, since the classification can be performed offline during a pre-processing phase. The examples presented in this paper demonstrate the importance of correctly clipping splats for high quality rendering. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Memory-Efficient Computation of Persistent Homology for 3D Images Using Discrete Morse Theory

    Page(s): 25 - 32
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (758 KB) |  | HTML iconHTML  

    We propose a memory-efficient method that computes persistent homology for 3D gray-scale images. The basic idea is to compute the persistence of the induced Morse-Smale complex. Since in practice this complex is much smaller than the input data, significantly less memory is required for the subsequent computations. We propose a novel algorithm that efficiently extracts the Morse-Smale complex based on algorithms from discrete Morse theory. The proposed algorithm is thereby optimal with a computational complexity of O(n2). The persistence is then computed using the Morse-Smale complex by applying an existing algorithm with a good practical running time. We demonstrate that our method allows for the computation of persistent homology for large data on commodity hardware. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Semi-automatic Navigation on 3D Triangle Meshes Using BVP Based Path-Planning

    Page(s): 33 - 40
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1141 KB) |  | HTML iconHTML  

    Efficient path-planning methods are being explored along the years to allow the movement of robots or virtual agents in planar environments. However, there is a lot of space to improve the quality of paths restricted to 3D surfaces, with holes and bends for instance. This work presents a new technique for path-planning on 3D surfaces called 3DS-BVP. This path planner is based on Boundary Value Problem (BVP), which generates potential fields whose gradient descent represents navigation routes from any point on the surface to a goal position. Resulting paths are smooth and free from local minima. The 3DS-BVP works on complex surfaces of arbitrary genus or curvature, represented by a triangle mesh, without the need of 2D parametrizations. Our results demonstrate that our technique can generate paths in arbitrary surfaces with similar quality as those generated by BVP-based methods in planar environments. Our approach can be applied in the development of new tools to automate the navigation on 3D surfaces, like the camera control in the exploratory visualization of 3D models. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Crowd Simulation: Improving Pedestrians' Dynamics by the Application of Lattice-Gas Concepts to the Social Force Model

    Page(s): 41 - 47
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (812 KB) |  | HTML iconHTML  

    The social force (SF) model has been successfully applied to the simulation of flows of pedestrians. Nevertheless, in some scenarios with low density, experiments show that the simulated individuals do not behave as expected, working as irrational particles rather than smart people. For example, by the means of the cited model, it is common to see many simulated individuals going several times straightly against columns, before finding a way to deviate and safely exit the room. Aiming to deal with such problems, this article proposes a way to provide the simulated pedestrians the ability of changing the direction of their displacement at reasonable times, in order to bypass eventually blocked or crowded near areas. To do so, it applies concepts from the lattice-gas model to the SF model. Experiments were driven in order to evaluate the proposed model. As results, it maintained the ability of the SF model to reproduce phenomena like the formation of arcs in evacuated one-door rooms. Focusing on the scenario with a column-blocked one-door room, the simulated pedestrians presented softer and more coherent trajectories, when compared to the pure SF model solution. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Automatic Detection of 2D Human Postures Based on Single Images

    Page(s): 48 - 55
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2849 KB) |  | HTML iconHTML  

    Estimating human pose in static images is a challenging task due to the high dimensional state space, presence of image clutter and ambiguities of image observations. In this paper we propose a method to automatically detect human poses in a single image, based on a 2D model combined with anthropometric data. Furthermore, we use artificial neural networks to detect high level information about the human posture. Experimental results showed that the proposed technique performs well in non trivial images. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Geodesic Conic Subdivision Curves on Surfaces

    Page(s): 56 - 63
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (627 KB) |  | HTML iconHTML  

    In this paper we present a nonlinear curve subdivision scheme, suitable for designing curves on surfaces. Starting with a geodesic control polygon with vertices on a surface, the scheme generates a sequence of geodesic polygons that converges to a continuous curve on the surface. In the planar case, the limit curve is a conic Bezier spline curve. Each section of the subdivision curve, corresponding to three consecutive points of the control polygon, depends on a free parameter which can be used to obtain a local control of the shape of the curve. Furthermore, it has the convex hull property. Results are extended to triangulated surfaces showing that the scheme is suitable for designing curves on these surfaces and has the convex hull property. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Real-Time Terrain Modeling Using CPU-GPU Coupled Computation

    Page(s): 64 - 71
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (896 KB) |  | HTML iconHTML  

    Motivated by the importance of having real-time feedback in sketch-based modeling tools, we propose a framework for terrain edition capable of generating and displaying complex and high-resolution terrains. Our system is efficient and fast enough to allow the user to see the terrain morphing at the same time the drawing edition occurs. We have two types of editing interactions: the user can draw strokes creating elevations and crevices, and previous strokes can be interactively moved to different regions of the terrain. One interesting feature of our tool is that terrain primitives can be interactively manipulated similarly to primitives in vector-graphics tools. We achieve real-time performance in both modeling and rendering using a hybrid CPU-GPU coupled solution. We maintain a coarse version of the terrain geometry in the CPU by using a quad tree, while a fine version is produced in the GPU using tessellation shaders. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Beam Casting Implicit Surfaces on the GPU with Interval Arithmetic

    Page(s): 72 - 77
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (658 KB) |  | HTML iconHTML  

    We present a GPU-based beam-casting method for rendering implicit surfaces in real time with antialiasing. We use interval arithmetic to model the beams and to detect their intersections with the surface. We show how beams can be used to quickly discard large empty regions in the image, thus leading to a fast adaptive subdivision method. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Sketch-Based Adaptive Mesh Augmentation Using Stellar Operators

    Page(s): 78 - 85
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4985 KB) |  | HTML iconHTML  

    In this paper we present a new method for modeling and editing surface detail using free-form curves and a natural interface. It combines in a original way an adaptive multiresolution mesh structure with a simple, intuitive sketch-based interface. One of the novel contributions of this work is the curve sensitive mesh resolution control, which allows the definition of a rich set of operators that locally modify the surface geometry. Furthermore, the present framework provides the basic functionality to build a complete feature based modeling system. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Visual Patterns in the Plant Kingdom

    Page(s): 86 - 92
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2483 KB) |  | HTML iconHTML  

    There has been a lot of progress in modeling and rendering elements of our Natural World for computer graphics tasks. In the Plant Kingdom, techniques for modeling the visual patterns presented in many natural objects (such as stripes on a watermelon) have advanced far less than methods for modeling the shape and reflectance properties of individual or large collections of elements (such as leaves and trees). In this paper we explore a procedural model for synthesis of many familiar visual patterns from the Plant Kingdom. Our results show that in this context a procedural model has advantages over other texturing techniques such as texture mapping and procedural noise, since these patterns are usually needed in great quantity, and at least for some plants, with many geometric variation, assigning consistent texture coordinates is a challenge. We show results for fruits, mushrooms, and small decorative plants. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Accurate Volume Rendering of Unstructured Hexahedral Meshes

    Page(s): 93 - 100
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (763 KB) |  | HTML iconHTML  

    Important engineering applications use unstructured hexahedral meshes for numerical simulations. Hexahedral cells, when compared to tetrahedral ones, tend to be more numerically stable and to require less mesh refinement. However, volume visualization of unstructured hexahedral meshes is challenging due to the trilinear variation of scalar fields inside the cells. The conventional solution consists in subdividing each hexahedral cell into five or six tetrahedra, approximating a trilinear variation by a piecewise linear function. This results in inaccurate images and increases the memory consumption. In this paper, we present an accurate ray-casting volume rendering algorithm for unstructured hexahedral meshes. In order to capture the trilinear variation along the ray, we propose the use of quadrature integration. A set of computational experiments demonstrates that our proposal produces accurate results, with reduced memory footprint. The entire algorithm is implemented on graphics cards, ensuring competitive performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.