1,721,055 research outputs found
Multiresolution MAP Despeckling of SAR Images Based on Locally Adaptive Generalized Gaussian pdf Modeling
No full textIn this paper, a new despeckling method based on undecimated wavelet decomposition and maximum a posteriori (MAP) estimation is proposed. Such a method relies on the assumption that the probability density function (pdf) of each wavelet coefficient is generalized Gaussian (GG). The major novelty of the proposed approach is that the parameters of the GG pdf are taken to be space-varying within each wavelet frame. Thus, they may be adjusted to spatial image context, not only to scale and orientation. Since the MAP equation to be solved is a function of the parameters of the assumed pdf model, the variance and shape factor of the GG function are derived from the theoretical moments, which depend on the moments and joint moments of the observed noisy signal and on the statistics of speckle. The solution of the MAP equation yields the MAP estimate of the wavelet coefficients of the noise-free image. The restored SAR image is synthesized from such coefficients. Experimental results, carried out on both synthetic speckled images and true SAR images, demonstrate that MAP filtering can be successfully applied to SAR images represented in the shift-invariant wavelet domain, without resorting to a logarithmic transformatio
Generalised stop-and-wait protocol
No full textAutomatic-repeat-request (ARQ) protocols are widely used in digital communication systems for their high reliability and simple implementation. Of the various ARQ schemes, the stop-and-wait is the simplest in terms of structure, but it achieves low throughput values, even for high signal-to-noise ratios. In the Letter a generalised stop-and-wait protocol is proposed. In this protocol some consecutive messages are sent during a transmission cycle before each stop and waiting period. This protocol retains the implementation simplicity of the classical stop-and-wait scheme, but results in a significant improvement in throughput
Source Coding and Transmission of HDTV Images with the Wavelet Transform
No full textDigital high-definition TV (HDTV) signals are generally compressed to reduce transmission bandwidth requirements. This paper presents a compression algorithm for the bit rate reduction of an HDTV image using the wavelet transform. The major problems related to the transmission of a compressed HDTV signal are analyzed. Transmission is examined both on a noisy channel and an asynchronous transfer mode (ATM) network. The effects of channel noise on the reconstructed image are determined, and a solution to mitigate the degradation of the image quality is presented. Lastly, a model for the output bit rate of the HDTV coder is derived and used to simulate the transmission of an ATM multiplexer so that the network's main performance parameters can be determined
ATM Transmission of HDTV Coded by the Wavelet Transform
No full textWavelet transform is applied to still images to implement a scalable coder. Scalability is exploited in packet transmission to avoid congestio
Volumetric interpolation of tomographic sequences for accurate 3D reconstruction of anatomical parts
No full textBackground and objective:Tomographic sequences of biomedical images are commonly used to achieve a three-dimensional visualization of the human anatomy. In some cases, the number of images contained in the sequence is limited, e.g., in low-dose computed tomography acquired on neonatal patients, resulting in a coarse and inaccurate 3D reconstruction. Methods:In this paper, volumetric image interpolation methods, devised to increase the axial resolution of tomographic sequences and achieve a refined 3D reconstruction, are proposed and compared. The techniques taken into consideration are based on motion-compensated frame-interpolation concepts, which have been developed for video applications, mainly frame-rate conversion. Results: The performance of the proposed methods is quantitatively assessed by using sequences with a simulated low axial resolution obtained from the decimation of standard high-resolution computed tomography sequences. Real data with an actual low axial resolution have been used as well for a qualitative evaluation of the proposed methods. Conclusions:The experimental results demonstrate that the proposed methods enable an effective slice interpolation and that the achievable 3D models clearly benefit from the increased axial resolution
Restoration of images corrupted by multiplicative noise in the nonsubsampled contourlet domain
No full textThe nonsubsampled contourlet transform (NSCT) is a powerful and versatile tool that allows a multiresolution and directional representation to be achieved. In this paper, we propose an extension of two despeckling algorithms, proposed to restore SAR images and based on the undecimated separable wavelet transform, to work into the NSCT domain. The signal is modeled as affected by a multiplicative noise. The noise-free NSCT coefficients are estimated from the observed ones according to either the maximum-a-posteriori (MAP) or the linear minimum mean square error (LMMSE) criterion. The results show that the proposed restoration algorithms highly benefit from the fact of working into a multiresolution and multidirectional domain. ©2008 IEEE
ATM Transmission of Wavelet Transformed Video Images:the Impact of Cell Losses and Transmission Errors
No full textEffect of packet losses is analyzed in the transmission of pictures coded using the wavelet transform in an ATM environment
Adaptive quadratic regularization for baseline wandering removal in wearable ECG devices
No full textThe electrocardiogram (ECG) is one of the most important physiological signals to monitor the health status of a patient. Technological advances allow the size and weight of ECG acquisition devices to be strongly reduced so that wearable systems are now available, even though the computational power and memory capacity is generally limited. An ECG signal is affected by several artifacts, among which the baseline wandering (BW), i.e., a slowly varying variation of its trend, represents a major disturbance. Several algorithms for BW removal have been proposed in the literature. In this paper, we propose new methods to face the problem that require low computational and memory resources and thus well comply with a wearable device implementation
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