Shape representation and coding of visual objets in multimedia applications — An overview

Emerging multimedia applications have created the need for new functionalities in digital communications. Whereas existing compression standards only deal with the audio-visual scene at a frame level, it is now necessary to handle individual objects separately, thus allowing scalable transmission as well as interactive scene recomposition by the receiver. The future MPEG-4 standard aims at providing compression tools addressing these functionalities. Unlike existing frame-based standards, the corresponding coding schemes need to encode shape information explicitly. This paper reviews existing solutions to the problem of shape representation and coding. Region and contour coding techniques are presented and their performance is discussed, considering coding efficiency and rate-distortion control capability, as well as flexibility to application requirements such as progressive transmission, low-delay coding, and error robustnes

Anisotropic Mesh Generation with Particles

Many important real-world problems require meshing, that is the approximation of a given geometry by a set of simpler elements such as triangles or quadrilaterals in two dimensions, and tetrahedra or hexahedra in three dimensions. Applications include finite element analysis and computer graphics. This work focuses on the former. A physically-based model of interacting "particles" is introduced to uniformly spread points over a 2-dimensional polygonal domain. The set of points is triangulated to form a triangle mesh. Delaunay triangulation is used because it guarantees a low computational cost and reasonably well-shaped elements. Several particle interaction (repulsion and attraction) models are investigated ranging from Gaussian energy potentials to Laplacian smoothing. Particle population control mechanisms are introduced to make the size of the mesh elements converge to the desired size. In most applications spatial mesh adaptivity is desirable. Triangles should not only adapt in si..

A Simple And Efficient Binary Shape Coding Technique Based On Bitmap Representation

This document presents a technique based on the JBIG algorithm for binary shape coding in both lossless and lossy modes. Because it is applied directly to the bitmap representing the shape information, it bypasses the overhead in computation of an intermediate contour representation and its associated conversions. This leads to a simpler algorithm which is more suitable for a larger class of shape data. In addition a mechanism is proposed which allows a rate control for lossy coding mode. 1. INTRODUCTION Second generation video coding algorithms are also referred to as object oriented, that is, the scene to be coded is segmented into several regions, each of them coded separately. These regions generally identify objects. Each object is represented by four channels: three color channels and an alpha channel which defines the shape of the object. This alpha channel can be either binary or multilevel. The multilevel case allows for semi-transparent object. However the scope of this pape..

Bounded-uncertainty estimation for correlated signal and noise

In this paper we present a class of bounded-uncertainty estimators as the solution of a classic estimation problem involving unknown statistics. The estimators are derived under the non-typical assumption of correlated signal and noise. The boundeduncertainty framework gives an additional degree of freedom for estimator design that can benefit its performance. It also provides an indirect way of verifying hypotheses regarding unknown variable statistics in a particular application domain by examining the behavior of the estimators as a function of the bound(s). If the unknown statistics are within a lower bound than the worst-case limit assumed by a classic minimax estimator, the quality of the estimation is increased by this new approach. I

A Pliant Method for Anisotropic Mesh Generation

A new algorithm for the generation of anisotropic, unstructured triangular meshes in two dimensions is described. Inputs to the algorithm are the boundary geometry and a metric that specifies the desired element size and shape as a function of position. The algorithm is an example of what we call pliant mesh generation. Itfirstconstructs the constrained Delaunay triangulation of the domain, then iteratively smooths, refines, and retriangulates. On each iteration, a node is selected at random, it is repositioned according to attraction/repulsion with its neighbors, the neighborhood is retriangulated, and nodes are inserted or deleted as necessary. All operations are done relative to the metric tensor. This simple method generates high quality meshes whose elements conform well to the requested shape metric. The method appears particularly well suited to surface meshing and viscous flow simulations, where stretched triangles are desirable, and to time-dependent remeshing problems

Region Based Coding Scheme with Scalability Features

In order to satisfy the needs of new applications in a multi-resolution environment the problem of object-- oriented coding has to be addressed. In this paper two main approaches are presented to tackle this problem. First, an algorithm for shape coding is presented. It is based on a chain coding algorithm where powerful modeling techniques are used to increase the compression ratio. Second, an algorithm for interior coding is described. It is based on an arbitrarily--shaped subband transform followed by a generalized embedded zerotree wavelet algorithm. It is shown in the paper that it achieves good compression results and has additional properties such as supporting arbitrarily--shaped regions, being computationally efficient, keeping the same dimensionality in the transformed domain, being perfect reconstruction, and allowing a perfect rate control. The presented results show that the two algorithms build an efficient basis to design object--oriented video coding schemes. 1 Introdu..

Efficient Compression of Non-Manifold Polygonal Meshes

We present a method for compressing non-manifold polygonal meshes, i.e., polygonal meshes with singularities, which occur very frequently in the real-world. Most efficient polygonal compression methods currently available are restricted to a manifold mesh: they require converting a non-manifold mesh to a manifold mesh, and fail to retrieve the original model connectivity after decompression. The present method works by converting the original model to a manifold model, encoding the manifold model using an existing mesh compression technique, and clustering, or stitching together during the decompression process vertices that were duplicated earlier to faithfully recover the original connectivity. This paper focuses on efficiently encoding and decoding the stitching information. Using a naive method, the stitching information would incur a prohibitive cost, while our methods guarantee a worst case cost of O(logm) bits per vertex replication, where m is the number of non-manifold vertices. Furthermore, when exploiting the adjacency between vertex replications, many replications can be encoded with an insignificant cost. By interleaving the connectivity, stitching information, geometry and properties, we can avoid encoding repeated vertices (and properties bound to vertices) multiple times; thus a reduction of the size of the bit-stream of about 10% is obtained compared with encoding the model as a manifold