Document image compression reduces the storage requirements for digitised books or documents by using characters as the fundamental unit of compression. Compression gains can be achieved by identifying regions that contain text, isolating unique characters, and storing them in a codebook. This thesis investigates several fundamental areas of the compression process. Algorithms for each area are tested on a corpus of images and the improvements tested for statistical significance. Methods for isolating characters from a bitmap are investigated along with techniques for determining reading order. We introduce the use of the docstrum to aid image compression and show that it improves upon previous methods. The Hough transform is shown to be an accurate method for determining page skew and gives robust results over a range of image resolutions. Compression is shown to improve when the skew of an image is determined automatically, and used to determine reading order. If images can be segm...

We have examined the tradeoffs in applying regular and Compressed Bloom filters to the name query problem in distributed file systems and developed and tested a novel mechanism for scaling queries as the network grows large. Filters greatly reduced query messages when using Fan's "Summary Cache" in web cache hierarchies[6], a similar albeit smaller, searching problem. We have implemented a testbed that models a distributed file system and run experiments that test various configurations of the system to see if Bloom filters could provide the same kind of improvements. In a realistic system, where the chance that a randomly queried node holds the file being searched for is low, we show that filters always provide lower bandwidth /search and faster time/search, as long as the rates of change of the files stored at the nodes is not extremely high relative to the number of searches. In other words, we confirm the intuition that keeping some state about the contents of the rest of the system will aid in searching as long as acquiring this state is not overly costly and it does not expire too quickly.

A determinacao de pontos de intersecao e contatos entre fronteiras de objetos nao e uma tarefa simples. Uma forma de facilitar essa operacao usa-se estruturas hierarquicas para issolar rapidamente os pedacos de segmentos em possvel intersecao, para finalmente se computar localmente os pontos de contato. Neste trabalho formula-se um novo metodo de representacao em estrutura hierarquica de caixas orientadas envolventes adaptado e ajustadamente de segmentos de fronteiras de objetos definidos por curvas B-splines cubicas fechadas com perturbacoes. Cada par de caixas adjacentes de um nvel define uma outra caixa orientada. Cada caixa e computada de forma adatada e ajustada aos segmentos de fronteira do objeto usando-se indicadores estatsticos de segunda ordem. O resultado computacional, em anima coes de objetos rgidos de geometria complexa em computacao grafica, mostra que o metodo formulado e eficiente comparado com outros metodos existentes.