Electronics and Communications in Japan (Part III: Fundamental Electronic Science)最新文献

When speech at a location away from a microphone is received, the received speech is degraded by reverberation in a room. To deal with this problem, a semiblind dereverberation method has been proposed in which no prior measurement of the room impulse response is used. However, the fast computation was required because an enormous amount of computation is needed for inverse filter calculation. In this paper, an acceleration method for the inverse filter calculation in the semiblind dereverberation method is proposed. For speed enhancement, the similarity of the correlation matrix to the convolution matrix is considered. By using fast convolution by the FFT in the conjugate gradient method, a dramatic increase in computation speed is achieved. A real-time dereverberation system was constructed on a personal computer by installing the proposed method and was tested in an actual environment. It was confirmed that the proposed method can achieve high-speed operation without degradation of dereverberation performance. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(7): 25–36, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20292

For image compression, frequency conversions such as the discrete cosine transform (DCT) and the wavelet transform (DWT) have been widely used. The multiplier coefficients used in these conversions are in general defined as real numbers, but they are approximated by a finite word length in the hardware configuration. This causes degradation of the reconstructed images due to mismatch of the coefficient values for the forward and backward transforms. In order to reduce the degradation of the reconstructed images caused by coefficient mismatch, a sufficiently long word length can be provided in setting the finite word length. However, since the compressed image data undergo quantization processing prior to entropy encoding in general, a word length greater than a certain length causes redundancy. Hence, this paper proposes a method in which the coefficient values of each multiplier are provided by the signed power-of-two (SPT) representation, using a sum of powers of 2 with as small a (finite) number of terms as possible, so that the error caused by coefficient mismatch is smaller than the error caused by quantization. In this way, a minimum-size wavelet circuit can be constructed in which the effect of coefficient mismatch between the forward and backward transformations cannot be visually recognized. It was experimentally confirmed by an experiment using the HDL language that the size of the circuit configuration used in the proposed method could be reduced by about 50% in comparison with the circuit in which the sum of the same number of powers of 2 is assigned to each multiplier coefficient. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(7): 47– 57, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20272

The wavelet transform has been used for image compression, image restoration, signal processing, and pattern recognition. In most cases, processing is performed with a scalar wavelet using one scaling function. However, the scalar wavelet has the deficiency that the properties of shortness of support, regularity, orthogonality, and high vanishing moment are not shared at the same time. Recently, the multiwavelet, consisting of several scaling functions and several wavelet functions, has been proposed. Since several input data are obtained by preprocessing in the multiwavelet transform, many studies of applications of the multiwavelet in the fields of signal processing and image processing are being carried out. Many engineering achievements have been reported. However, little has been reported on the use of multiwavelets for restoration of degraded images. This is a research field with prospects for future growth. In the present research, a threshold shrinking method is proposed in which different threshold values are used for the horizontal, vertical, and diagonal directions at each level and also within the same level in the multiwavelet domain for degraded images with superimposed Gaussian noise. The effectiveness of the proposed method is demonstrated by a computer simulation. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(7): 15– 24, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20295

This paper proposes a novel data hiding method for JPEG 2000 coded images that embed multi-level information into quantized discrete wavelet transformed coefficients. Since the proposed method hides information represented as an integer to a transformed coefficient rounded to an integer, a JPEG 2000 code-stream conveying data keeps its standard JPEG 2000 code-stream structure. The proposed method is able to extract hidden data without memorizing embedding positions; it thus chooses transformed coefficients to which data is hidden freely. This characteristic makes the proposed method suitable for hiding data to a JPEG 2000 coded image with consideration of Region of Interest (ROI) coding that is a major feature. Simulation results show the effectiveness of the proposed method. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(7): 37– 46, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20286