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Browsing by Author "Francisco, Nelson C."

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  • Compression of touchless multiview fingerprints
    Publication . Francisco, Nelson C.; Zaghetto, Alexandre; Macchiavello, Bruno; Silva, Eduardo A. B. da; Lima-Marques, Mamede; Rodrigues, Nuno M. M.; Faria, Sergio
    Recently, touchless multiview fingerprinting technology has been proposed as an alternative to overcome the intrinsic problems of traditional contact-based systems. Nevertheless, compression of this kind of signal has not been fully evaluated and standardized. This paper investigates the comparative performance of several encoders for this data, namely WSQ, JPEG2000, H.264/AVC and MMP. Experimental results show that WSQ encoder, which is the current compression standard for contact-based fingerprints, is objectively outperformed by all others. In particular, MMP, which achieved the best results, outperforms WSQ by up to 4 dB.
    2011-09Conference paper Open access Show more
  • Computational complexity reduction methods for multiscale recurrent pattern algorithms
    Publication . Francisco, Nelson C.; M. M. Rodrigues, Nuno; Silva, Eduardo A. B. da; Carvalho, Murilo B. de; Faria, Sergio
    The Multidimensional Multiscale Parser algorithm was originally proposed as a generic lossy data compression algorithm. An high degree of adaptivity and versatility allowed it to outperform state-of-the-art transform-based compression methods for a wide range of applications, from still images, compound documents, or even ECG's, just to name a few. However, as other pattern matching algorithms, it presents a high computational complexity. In this paper, we investigated several techniques that allowed to considerably reduce both the encoder's and the decoder's computational complexity, with marginal R-D performance losses. The most important reduction was achieved on the decoder, that reduced up to 95% the time required by the previous method. These improvements contribute to affirm MMP as an alternative to traditional transform-based encoders, approaching its computational complexity with that of transform-based algorithms.
    2011-04Conference paper Open access Show more
  • A generic post-deblocking filter for block based image compression algorithms
    Publication . Francisco, Nelson C.; Rodrigues, Nuno M. M.; Silva, Eduardo A.B. da; Faria, Sérgio M.M. de
    In this paper we propose a new post-processing deblocking technique that is independent of the compression method used to encode the image. The development of this filter was motivated by the use of Multidimensional Multiscale Parser (MMP) algorithm, a generic lossy and lossless compression method. Since it employs an adaptive block size, it presents some impairments when using the deblocking techniques presented in the literature. This led us to the development of a new and more generic deblocking method, based on total variation and adaptive bilateral filtering. The proposed method was evaluated not only for still images, but also for video sequences, encoded using pattern matching and transform based compression methods. For all cases, both the objective and subjective quality of the reconstructed images were improved, showing the versatility of the proposed technique.
    2012-10Journal article Restricted access Show more
  • Scanned Compound Document Encoding Using Multiscale Recurrent Patterns
    Publication . Francisco, Nelson C.; Rodrigues, Nuno M. M.; Silva, Eduardo A. B. da; Carvalho, Murilo Bresciani de; Faria, Sérgio M. M. de; Silva, Vitor M. M.
    In this paper, we propose a new encoder for scanned compound documents, based upon a recently introduced coding paradigm called multidimensional multiscale parser (MMP). MMP uses approximate pattern matching, with adaptive multiscale dictionaries that contain concatenations of scaled versions of previously encoded image blocks. These features give MMP the ability to adjust to the input image's characteristics, resulting in high coding efficiencies for a wide range of image types. This versatility makes MMP a good candidate for compound digital document encoding. The proposed algorithm first classifies the image blocks as smooth (texture) and nonsmooth (text and graphics). Smooth and nonsmooth blocks are then compressed using different MMP-based encoders, adapted for encoding either type of blocks. The adaptive use of these two types of encoders resulted in performance gains over the original MMP algorithm, further increasing the performance advantage over the current state-of-the-art image encoders for scanned compound images, without compromising the performance for other image types.
    2010-09-17Journal article Restricted access Show more