Análise da transformada wavelet direcional adaptativa na codificação de imagens

AUTOR(ES)

Karen França de Oliveira

DATA DE PUBLICAÇÃO

2009

RESUMO

This work presents a method for the numerical stability analysis of adaptive lifting-based directional transforms. The goal is to investigate the relation between the directions set in the lifting scheme and the reconstruction quality of the corresponding bases. This new method is based on the variation in frequency of the condition number of the synthesis polyphase transfer matrix of multimensional directional filter banks. The implemented transforms, characterized by such filters, allows for the adaptation of the filtering directions to match the local directionality of the image features, resulting in lower energy of the high-frequency subbands. In order to do so, the (6,6) interpolating wavelet kernel was modified, inserting directional information into the lifting steps. Different methods were suggested to determine the optimal set of directions, in terms of maximizng compression performance. Best results pointed to the prediction direction choice based on the distortion minimization algorithm, followed by the update step in the same direction. In order to test the directional transforms, the transform modules of JPEG2000 and SPIHT coders were replaced by the aforementioned transform algorithm. In this way, one can really achieve higher energy compaction for images with abrupt transitions. Next, we carried a numerical stability analysis based on the variation in frequency of the condition number of the transform. Results have shown that bases generated by using the prediction direction different from the update direction actually leads to worse reconstruction quality. As the transform is one of the crucial elements in transform coding systems, improvements in that module may effectivelly lead to overall coding improvements.

ASSUNTO(S)

número de condição transofrmadas wavelet engenharia eletrica codificação de imagem filtragem adaptativa lifting direcional

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