Connected-component labeling

Résumé

Connected-component labeling (CCL), connected-component analysis (CCA), blob extraction, region labeling, blob discovery, or region extraction is an algorithmic application of graph theory, where subsets of connected components are uniquely labeled based on a given heuristic. Connected-component labeling is not to be confused with . Connected-component labeling is used in computer vision to detect connected regions in s, although s and data with higher dimensionality can also be processed. When integrated into an system or human-computer interaction interface, connected component labeling can operate on a variety of information. Blob extraction is generally performed on the resulting from a thresholding step, but it can be applicable to gray-scale and color images as well. Blobs may be counted, filtered, and tracked. Blob extraction is related to but distinct from blob detection. Overview A graph, containing vertices and connecting edges, is constructed from relevant

Source officielle

https://en.wikipedia.org/wiki/Connected-component_labeling

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Generalized Codes on Graphs and Applications in Content Distribution

Masoud Alipour Babaei

The contribution of this thesis is twofold. In the first part, we generalize and analyze two classes of error correcting codes: LDPC codes and product codes. We generalize graphical codes by considering checks being arbitrary codes instead of single parities. We analyze the performance of these codes under message passing decoding by using an extended density evolution over erasure channels. Further, we provide an optimal instance of these codes having rates arbitrarily close to the capacity of any binary symmetric channel where a belief propagation algorithm is used for decoding. The relation to other similar constructions is discussed as well. In a similar approach, we introduce irregular product codes, a class of codes where each codeword is represented by a matrix and the entries in each row (column) of the matrix come from a component row (column) code. Unlike product codes, we do not require that all component row and column codes be the same. This relaxation offers additional flexibility and features such as allowing some regions of the codeword to be more error-resilient, providing a more refined spectrum of rates for finite lengths, and improved performance for some of these rates. We study these codes over erasure channels and prove that for many rate distributions on component row codes, there is a matching rate distribution on component column codes such that an irregular product code based on MDS codes with those rate distributions on the component codes has an optimal asymptotic rate. In the second part we consider two novel applications of Raptor codes. Raptor codes are a class of fountain codes which present excellent performance, flexibility, and low decoding complexity over erasure channels. The data synchronization in an IP multicasting scenario involves reflecting changes from a content on a server to multiple clients efficiently. All these clients possess a slightly different copy of the content on the server. Existing methods are a direct extension of the point-to-point setting which is not necessarily optimal in terms of the total bandwidth usage in the multicast setting. We review this problem and its related information theoretic bounds. We propose and analyze an algorithm using Raptor codes which takes advantage of the multicast protocol to address this problem effectively. This method is close to optimal in terms of the amount of required transmitted information and the network usage. In another application, we show how to make satellite Digital Video Broadcasting resilient to signal jamming by distributing programs over multiple satellite links. However, leasing extra bandwidth on satellite links incurs supplementary cost to the broadcasting operator. In our solution we employ Raptor codes to make the bandwidth usage efficient and adaptive according to the link conditions. The proposed solution is fully compatible with the existing standards and infrastructure.

EPFL2013

Chargement

Irregular Product Codes

Masoud Alipour Babaei, Seyed Omid Etesami, Ghid Maatouk, Mohammad Amin Shokrollahi

We introduce irregular product codes, a class of codes where each codeword is represented by a matrix and the entries in each row (column) of the matrix come from a component row (column) code. As opposed to standard product codes, we do not require that all component row codes nor all component column codes be the same. Relaxing this requirement can provide some additional attractive features such as allowing some regions of the codeword to be more error-resilient, providing a more refined spectrum of rates for finite lengths, and improved performance for some of these rates. We study these codes over erasure channels and prove that for any 0 < ε < 1, for many rate distributions on component row codes, there is a matching rate distribution on component column codes such that an irregular product code based on MDS codes with those rate distributions on the component codes has asymptotic rate 1 - ε and can decode on erasure channels having erasure probability

Ieee2012

Chargement

, , ,

Tracking moving objects is a critical step for smart video surveillance systems. Despite the complexity increase, multiple camera systems exhibit the undoubted advantages of covering wide areas and handling the occurrence of occlusions by exploiting the different viewpoints. The technical problems in multiple camera systems are several: installation, calibration, objects matching, switching, data fusion, and occlusion handling. In this paper, we address the issue of tracking moving objects in an environment covered by multiple un-calibrated cameras with overlapping fields of view, typical of most surveillance setups. Our main objective is to create a framework that can be used to integrate object-tracking information from multiple video sources. Basically, the proposed technique consists of the following steps. We first perform a single- view tracking algorithm on each camera view, and then apply a consistent object labeling algorithm on all views. In the next step, we verify objects in each view separately for inconsistencies. Correspondent objects are extracted through a Homography transform from one view to the other and vice versa. Having found the correspondent objects of different views, we partition each object into homogeneous regions. In the last step, we apply the Homography transform to find the region map of first view in the second view and vice versa. For each region (in the main frame and mapped frame) a set of descriptors are extracted to find the best match between two views based on region descriptors similarity. This method is able to deal with multiple objects. Track management issues such as occlusion, appearance and disappearance of objects are resolved using information from all views. This method is capable of tracking rigid and deformable objects and this versatility lets it to be suitable for different application scenarios.

2009

Chargement

Generalized Codes on Graphs and Applications in Content Distribution

Masoud Alipour Babaei

EPFL2013