Resumo-Este artigo propõe uma técnica para a detecção e correção de ruído presente em sinais de vídeo, independente do método de codificação utilizado. Tal técnica se baseia no uso da propriedade de regularidade das wavelets para a definição de uma figura de mérito que favorece a construção de características de decaimento dos coeficientes wavelet de cada cena. Através desse procedimento, pode-se obter a reconstrução de pixels que sejam classificados como contaminados por ruído. O método tem se mostrado mais eficiente na identificação e correção de quadros corrompidos, comparativamente a outros algoritmos de correção de erro encontrados na literatura corrente, operando no domínio espaço-temporal. Resultados satisfatórios são obtidos tanto em termos subjetivos quanto da PSNR.Palavras-Chave-Correção de erro, correlação entre escalas, regularidade, transformada wavelet.
In digital filters theory, filtering techniques generally deal with pole-zero structures. In this context, filtering schemes, such as infinite impulse response (IIR) filters, are described by linear differential equations or linear transformations, in which the impulse response of each filter provides its complete characterization, under filter design specifications. On the other hand, finite impulse response (FIR) digital filters are more flexible than the analog ones, yielding higher quality factors. Since many approaches to the circuit synthesis using the wavelet transform have been recently proposed, here we present a digital filter design algorithm, based on signal wavelet decomposition, which explores the energy partitioning among frequency sub-bands. Exploring such motivation, the method involves the design of a perfect reconstruction wavelet filter bank, of a suitable choice of roots in the Z-plane, through a spectral factorization, exploring the orthogonality and localization property of the wavelet functions. This approach resulted in an energy partitioning across scales of the wavelet transform that enabled a superior filtering performance, in terms of its behavior on the pass and stop bands. This algorithm presented superior results when compared to windowed FIR digital filter design, in terms of the intended behavior in its transition band. Simulations of the filter impulse response for the proposed method are presented, displaying the good behavior of the method with respect to the transition bandwidth of the involved filters.
Inpainting methods play a major role in image processing, minimizing the effects of data block loss in image transmission. They analyze primarily the spatial correlation between the portions of an image, usually without explicitly exploring information on the frequency domain. Techniques that evaluate losses of blocks in images do not locally describe a figure of merit for consistent measurement of spatial correlation between pixels of each corrupted block. This investigation presents a digital image inpainting technique, extensible to video applications, using the property of wavelet regularity in multiresolution image analysis, described locally in the sense of Besov vector spaces. Their generalized smoothness allows widespread changes in wavelet coefficients of image data, concealing errors in visual information. This technique estimates decay curves of wavelet coefficients from pixels, based in the observation of the regularity property, correcting pixel blocks contaminated by noise. This investigation proposes an algorithm in the wavelet transform domain, which detects and fixes damaged pixel blocks from a designed decay function for wavelet coefficients. Simulation results, obtained in corrupted images by several noise patterns, indicated better performance of this methodology when compared with other ones. INDEX TERMS Wavelet transforms, image processing, image quality.
This paper prcsents an improved embedded zerotree wavelet (EZW) coding algorithm, which makes use of the wavelet regularity to derive a classification criterion of wavelet coefficients in spatial-oricntation hierarchical trees. Variations of the EZW algorithm discussed in the opcn literahre have proposed some modifications in the process of exploiting the similarity of coefficients through the scales, however, not defining a figure of mcrit to measure such a similarity.Simulation results achieved from the coding of well-known images in thc literature, for seveid bit rates, show a better performance of the proposed algorithm in both PSNR and subjective terms, as compared with EZW and SPIHT algorithms.
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