Self-organising maps : statistical analysis, treatment and applications.

This thesis presents some substantial theoretical analyses and optimal treatments of Kohonen's self-organising map (SOM) algorithm, and explores the practical application potential of the algorithm for vector quantisation, pattern classification, and image processing. It consists of two major parts. In the first part, the SOM algorithm is investigated and analysed from a statistical viewpoint. The proof of its universal convergence for any dimensionality is obtained using a novel and extended form of the Central Limit Theorem. Its feature space is shown to be an approximate multivariate Gaussian process, which will eventually converge and form a mapping, which minimises the mean-square distortion between the feature and input spaces. The diminishing effect of the initial states and implicit effects of the learning rate and neighbourhood function on its convergence and ordering are analysed and discussed. Distinct and meaningful definitions, and associated measures, of its ordering are presented in relation to map's fault-tolerance. The SOM algorithm is further enhanced by incorporating a proposed constraint, or Bayesian modification, in order to achieve optimal vector quantisation or pattern classification. The second part of this thesis addresses the task of unsupervised texture-image segmentation by means of SOM networks and model-based descriptions. A brief review of texture analysis in terms of definitions, perceptions, and approaches is given. Markov random field model-based approaches are discussed in detail. Arising from this a hierarchical self-organised segmentation structure, which consists of a local MRF parameter estimator, a SOM network, and a simple voting layer, is proposed and is shown, by theoretical analysis and practical experiment, to achieve a maximum likelihood or maximum a posteriori segmentation. A fast, simple, but efficient boundary relaxation algorithm is proposed as a post-processor to further refine the resulting segmentation. The class number validation problem in a fully unsupervised segmentation is approached by a classical, simple, and on-line minimum mean-square-error method. Experimental results indicate that this method is very efficient for texture segmentation problems. The thesis concludes with some suggestions for further work on SOM neural networks

S-TREE: Self-Organizing Trees for Data Clustering and Online Vector Quantization

This paper introduces S-TREE (Self-Organizing Tree), a family of models that use unsupervised learning to construct hierarchical representations of data and online tree-structured vector quantizers. The S-TREE1 model, which features a new tree-building algorithm, can be implemented with various cost functions. An alternative implementation, S-TREE2, which uses a new double-path search procedure, is also developed. S-TREE2 implements an online procedure that approximates an optimal (unstructured) clustering solution while imposing a tree-structure constraint. The performance of the S-TREE algorithms is illustrated with data clustering and vector quantization examples, including a Gauss-Markov source benchmark and an image compression application. S-TREE performance on these tasks is compared with the standard tree-structured vector quantizer (TSVQ) and the generalized Lloyd algorithm (GLA). The image reconstruction quality with S-TREE2 approaches that of GLA while taking less than 10% of computer time. S-TREE1 and S-TREE2 also compare favorably with the standard TSVQ in both the time needed to create the codebook and the quality of image reconstruction.Office of Naval Research (N00014-95-10409, N00014-95-0G57

Segmentación y detección de objetos en imágenes y vídeo mediante inteligencia computacional

Finalmente, se exponen las conclusiones obtenidas tras la realización de esta tesis y unas posibles líneas futuras de investigación. Fecha de lectura de Tesis: 17 diciembre 2018.La presente tesis trata sobre el procesamiento y análisis de imágenes y video mediante sistemas informáticos. Primeramente se hace una introducción, especificando contexto, objetivos y metodología. Luego se muestran los antecedentes, los fundamentos de la videovigilancia, las dificultades existentes y diversos algoritmos del estado del arte, seguido de las principales características del aprendizaje profundo, transporte inteligente y sistemas con cámara PTZ, finalizando con la evaluación de métodos y distintos conjuntos de datos. Después se muestran tres partes. La primera comenta los estudios desarrollados que tratan sobre segmentación. Aquí se explican diferentes modelos desarrollados cuyo objetivo es la detección de objetos, tanto usando hardware genérico o especifico como en ámbitos específicos, o un estudio de cómo influye la reducción del tamaño de las imágenes al rendimiento de los algoritmos. La segunda parte describe los trabajos que utilizan una cámara PTZ. El primero trabajo hace un seguimiento del objeto más anómalo del escenario, siendo el propio sistema el que decide cuáles son anómalos y cuáles no; el segundo muestra un sistema que indica a la cámara los movimientos a realizar en función de la salida producida por un modelo de fondo no panorámico y mejorada con un gas neuronal creciente. La tercera parte trata sobre los estudios desarrollados con relación con el transporte inteligente, como es la clasificación de los vehículos que aparecen en secuencias de tráfico. El primer trabajo aplica técnicas tradicionales como segmentación y extracción de rasgos; el segundo utiliza segmentación y redes convolucionales, complementado con un estudio del redimensionado de imágenes para proveerlas en el formato necesario a cada red; y el tercero emplea un modelo que detecta y clasifica objetos, estimando posteriormente la contaminación generada por los vehículos