2006 19th Brazilian Symposium on Computer Graphics and Image Processing

Sharp discontinuities in depth, or depth edges, are very important low-level features for scene understanding. Recently, we have proposed a solution to the depth edge detection problem using a simple modification of the capture setup: a multi-flash camera with flashes appropriately positioned to cast shadows along depth discontinuities in the scene. In this paper, we show that by varying illuminat... View full abstract»

In this work we propose a method for the polygonization of octree-based reconstructions by dual contouring. Dual contouring is an adaptive method for determining contiguous polygonal meshes from signed octrees. It determines the positioning of the vertices of the mesh by minimizing a quadratic error expressed in terms of hermitian data. In order to apply dual contouring on volumetric reconstructio... View full abstract»

Geometry processing applications estimate the local geometry of objects using information localized at points. They usually consider information about the normal as a side product of the points coordinates. This work proposes parabolic polygons as a model for discrete curves, which intrinsically combines points and normals. This model is naturally affine invariant, which makes it particularly adap... View full abstract»

In this work we address the problem of computing point-based surface approximations from point clouds. Our approach is based on recently presented methods that define the approximated surface as the set of stationary points for an operator that projects points in the space onto the surface. We present a novel projection operator that differs from the defined in previous work in that it uses princi... View full abstract»

Image segmentation using tree pruning (TP) and watershed (WS) has been presented in the framework of the image forest transform (IFT) - a method to reduce image processing problems related to connectivity into an optimum-path forest problem in a graph. Given that both algorithms use the IFT with similar parameters, they usually produce similar segmentation results. However, they rely on different ... View full abstract»

This paper addresses the problem of foreground extraction using active illumination and graph-cut optimization. Our approach starts by detecting image regions that are likely to belong to foreground objects. These regions are constituted by pixels where the difference in luminance for two differently illuminated images is large. The foreground objects are segmented by graph-cut optimization using ... View full abstract»

This paper makes a rereading of two successful image segmentation approaches, the fuzzy connectedness (FC) and the watershed (WS) approaches, by analyzing both by means of the image foresting transform (IFT). This graph-based transform provides a sound framework for analyzing and implementing these methods. This paradigm allows to show the duality existing between the WS by IFT and the FC segmenta... View full abstract»

Traditional mesh segmentation methods normally operate on geometrical models with no image information. On the other hand, 2D image-based mesh generation and segmentation counterparts, such as Imesh (A. Cuadros-Vargas et. al, 2005) perform the task by following a set of well defined rules derived from the geometry of the triangles, but with no statistical information of the mesh elements. This pap... View full abstract»

Region-based approaches to cel painting typically use shape similarity and topology relations between regions of consecutive animation frames. This paper presents a new colorization algorithm based on topological differences defined over a hierarchical graph of adjacent regions, which allows an almost full automatic colorization process. Also this paper discusses other attributes that improve the ... View full abstract»

This paper presents a new visually realistic animation technique for objects that melt and flow. It simulates viscoplastic properties of materials such as metal, plastic, wax, polymer and lava. The technique consists in modeling the object by the transition of a non-Newtonian fluid with high viscosity to a liquid of low viscosity. During the melting, the viscosity is formulated using the general N... View full abstract»

Crowded interactive environments composed of a large number of objects need a fast, accurate and scalable mechanism for collision detection. This work presents a detailed performance analysis of a hybrid collision detection algorithm for highly interactive and crowded environments. Extensive tests were conducted and the performance of the algorithm was evaluated in terms of output quality and runn... View full abstract»

Collision detection is an important problem in many kinds of applications. This work presents an efficient approach for exact collision detection between complex, deformable models. The approach consists of a method for fast extraction of semantics from transformation matrices which places models in a scene, together with a general strategy for fast intersection tests. Non-uniform scaling is also ... View full abstract»

In this paper, we present a novel method for estimating the effective number of independent variables in imaging applications that require multiple hypothesis testing. The method increases the statistical power of the results by refuting the assumption of independence among variables, while keeping the probability of false positives low. It is based on the spectral graph theory, in which the varia... View full abstract»

Statistical discrimination methods are suitable not only for classification but also for characterization of differences between a reference group of patterns and the population under investigation. In the last years, statistical methods have been proposed to classify and analyze morphological and anatomical structures of medical images. Most of these techniques work in high-dimensional spaces of ... View full abstract»

Recent statistics show that breast cancer is a major cause of death among women in all of the world. Hence, early diagnostic with computer aided diagnosis (CAD) systems is a very important tool. This task is not easy due to poor ultrasound resolution and large amount of patient data size. Then, initial image segmentation is one of the most important and challenging task. Among several methods for ... View full abstract»

The visualization of image structures in 3D obtained from computerized tomography examinations aids the medical professional in the analysis of images and consequently, provides a more accurate diagnoses. As these images (slices) are spaced apart it becomes necessary to fill in the empty spaces to show the structure in 3D. The use of the virtual slice between the real slices following the restorat... View full abstract»

Current methods that interactively render reasonably complex CSG objects are image based and are severely bandwidth limited. This paper presents a new approach to ray-tracing CSG objects composed of convex primitives that combines spatial subdivision and ray-tracing methods. By performing spatial subdivision on the CSG object until locally it is simple enough to be rendered effectively and efficie... View full abstract»

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 text... View full abstract»