EURASIP Journal on Advances in Signal Processing, 2019
In digital filters theory, filtering techniques generally deal with pole-zero structures. In this... more 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 lo... more 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 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 to other ones.
With the growing visual information signals transmission, methods of image inpainting acquired no... more With the growing visual information signals transmission, methods of image inpainting acquired noticeable importance in signal processing area. These methods, usually proposed to minimize the effects of loss of data blocks, analyze primarily the spatial correlation between portions of an image, without intensively exploring the information in the frequency domain. In another aspect, techniques that seek to evaluate losses of blocks in images do not describe locally a figure of merit for consistent measurement of spatial correlation between pixels of each corrupted block. In the context of exploring the visual information signal in multiple resolutions, this work presents a technique of digital image inpainting, extensible to video applications, from the analysis of property of regularity of wavelets in multiresolution analysis of images, described locally in the sense of Besov vectorial spaces, whose generalized smoothness allows widespread changes in wavelet coefficients of image data, aiming to conceal visual information. The study describes a technique for estimation of decay curves of the wavelet coefficients from pixels, based on observation of the property of regularity, aiming to correct blocks of pixels contaminated by noise. From the observation of such characteristics, the study proposes an algorithm for inpainting, in the wavelet transform domain, applied to images, performing as the detection task, based in a criterion of threshold of cross-correlation between wavelet coefficients, as the correction of damaged pixel blocks, stated in the reconstruction of information from a designed decay function for those coefficients. Simulation results obtained for the implementation of the method in images corrupted by different patterns of noise show its good performance compared to other recent methods. At the end of this work, topics to be explored in further research are presented.
International Journal of Electrical Engineering Education, 2013
The Microsoft ® Excel spreadsheet is a formidable educational tool but lacks native functions tha... more The Microsoft ® Excel spreadsheet is a formidable educational tool but lacks native functions that would allow easy working with complex numbers and polynomials, so preventing its widespread use in most electrical engineering courses. Such limitations could be overcome using the open source XNumbers add-in package, bringing to Excel new numerical capabilities which have been available to students only in high-end scientifi c packages, such as Matlab ® or Scilab. Here, we present an application of those features in control engineering courses, treating the specifi c case of a secondorder feedback system with dynamic response by the root-locus method.
An improved ezw algorithm based on set partitioning in hierarchical trees using wavelet regularity
This paper presents an improved embedded zerotree wavelet (EZW) coding algorithm, which makes use... more This paper presents 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-orientation hierarchical trees. Variations of the EZW algorithm discussed in the open literature have proposed some modifications in the process of exploiting the similarity of coefficients through the scales, however, not defining a figure of merit to measure such a similarity. Simulation results achieved from the coding of well-known images in the literature, for several 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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Papers by Sergio Penedo