Erratum to “Retinal Vessel Centerline Extraction Using Multiscale Matched Filters, Confidence and Edge Measures”

In order to detect vessels at a variety of widths, we apply the matched filter at multiple scales (i.e., compute for multiple values and then combine the responses across scales). Unfortunately, the output amplitudes of spatial operators such as derivatives or matched filters generally decrease with increasing scale. To compensate for this effect, Lindeberg introduced gamma-normalized derivatives. We use this notion to define a gamma-normalized matched filter     

基于FPGA的FIR数字滤波器设计与仿真

数字滤波作为数字信号处理技术的重要组成部分,广泛应用于信号分离、恢复、整形等场合.FIR滤波器因其严格的线性相位特性而应用广泛,通过系统研究数字滤波器的基本理论及基于FPGA的实现方法,给出利用MATLAB仿真软件设计出符合要求的数字滤波器并对其进行仿真验证.     

Commutativity and Application of Digital Interpolation Filters and Modulators

Interpolation filters are being widely used in a variety of communication applications. An equivalent realization of an interpolation FIR filter is shown to be a cascade combination of a hold and a periodically varying filter. It is also shown that the periodicity of the filter results in the Commutativity of the filter and a sinusoidal modulator. An application of such a scheme to TDM-FDM transmultiplexer is also presented.     

视频编码新技术和新方向

以HEVC和AVS2为代表的新一代视频编码标准,仍主要采用基于预测/变换的编码框架,但在编码单元、帧内预测、帧间预测和去块效应滤波等环节均引入了新的编码技术.对这些视频编码新技术进行了总结,同时分析和探讨了场景视频编码、云编码以及深度学习视频编码等视频技术发展新方向.     

Signal detection by complex spatial filtering

In the past, spatial filtering in coherent optical systems has been limited by the inability to realize practically a general complex filter. This paper describes a technique for realizing such a filter, and gives an application of spatial filtering to the problem of detecting isolated signals in a variety of noise backgrounds. The experimental results obtained to date indicate that this technique provides an excellent two-dimensional filtering capability that will play a key role in such problems as shape recognition and signal detection.     

The control of discrete event systems

A discrete event system (DES) is a dynamic system that evolves in accordance with the abrupt occurrence, at possibly unknown irregular intervals, of physical events. Such systems arise in a variety of contexts ranging from computer operating systems to the control of complex multimode processes. A control theory for the logical aspects of such DESs is surveyed. The focus is on the qualitative aspects of control, but computation and the related issue of computational complexity are also considered. Automata and formal language models for DESs are surveyed     

The indoor radio propagation channel

In this tutorial survey the principles of radio propagation in indoor environments are reviewed. The channel is modeled as a linear time-varying filter at each location in the three-dimensional space, and the properties of the filter's impulse response are described. Theoretical distributions of the sequences of arrival times, amplitudes and phases are presented. Other relevant concepts such as spatial and temporal variations of the channel, large-scale path losses, mean excess delay and RMS delay spread are explored. Propagation characteristics of the indoor and outdoor channels are compared and their major differences are outlined. Previous measurement and modeling efforts are surveyed, and areas for future research are suggested     

Sensitivities of Band-Edge Selectivities

Many filters have a band-edge selectivity (BES) that is a function of parameters other than filter order. In these cases, the band-edge selectivity can be maximized without increasing the order of the filter. However, in increasing BES, we must keep track of the sensitivity of BES to the parameters. In this paper, we provide sensitivities of BES to filter parameters for a variety of classical filters, these being described by rational functions approximating the ideal filter magnitude response. The results are useful in the design of such filters.     

Single-Post Inductive Obstacle in Rectangular Waveguide

A rapidly converging moment solution for electromagnetic scattering by a single inductive post in a rectangular waveguide is obtained. The numerical results show good agreement with Marcuvitz's data as far as this data goes. Furthermore, Marcuvitz's curves are extended to cover data for large posts. This new data should aflow one to design a simply constructed new type of narrow bandpass filter, namely, a filter consisting of large single posts. The successful use of this straightforward moment solution in solving the single-post problem suggests that this technique should prove useful in solving a variety of microwave discontinuities such as those involving thin or thick irises and posts of arbitrary shape.     

基于FPGA设计的FIR滤波器的实现与对比

描述了基于FPGA的FIR滤波器设计。根据FIR的原理及严格线性相位滤波器具有偶对称的性质给出了FIR滤波器的4种结构,即直接乘加结构、乘法器复用结构、乘累加结构、DA算法。在本文中给出上述几种算法的结构框图,并通过FPGA编程实现上述几种算法,并给出所用的资源来比较各种算法的优劣。     

基于最小平均相关能量滤波器的畸变目标识别

通过对多种畸变目标识别算法的研究, 对用于匹配滤波器的最小平均相关能量(MACE)滤波器进行了改进。利用MACE滤波器算法的基本思想构造滤波器函数, 在合成参考图像前对训练图像进行边缘提取, 并对联合图像的功率谱进行了拉普拉斯锐化, 成功实现了在联合变换相关器中对旋转目标图像的探测和识别, 提高了畸变图像相关峰的亮度, 拓展了联合变换相关器的探测和识别的范围。作为实例, 对旋转战机目标图像进行了计算机模拟实验和光学实验, 验证了该算法的可行性。     

Pulse-shaping filters with ISI-free matched and unmatched filterproperties

Pulse-shaping filters which have intersymbol-interference-free properties, with or without matched filtering at the receiver, may reduce the hardware cost of modem systems in some applications. A new class of such filters, with the one given by Xia (see ibid., vol.45, p.1157-58, 1997) as a special case, is proposed. This is done by showing that such a filter can be deduced from any one of a wide variety of ISI-free filters     

基于最小平均相关能量滤波器的畸变目标识别

通过对多种畸变目标识别算法的研究,对用于匹配滤波器的最小平均相关能量(MACE)滤波器进行了改进。利用MACE滤波器算法的基本思想构造滤波器函数,在合成参考图像前对训练图像进行边缘提取,并对联合图像的功率谱进行了拉普拉斯锐化,成功实现了在联合变换相关器中对旋转目标图像的探测和识别,提高了畸变图像相关峰的亮度,拓展了联合变换相关器的探测和识别的范围。作为实例,对旋转战机目标图像进行了计算机模拟实验和光学实验,验证了该算法的可行性。     

Multilevel nonlinear filters for edge detection and noisesuppression

Two new classes of multilevel nonlinear filters are introduced for simultaneous edge detection and noise suppression, which the authors call a nested median filter/median averaging filter (NMF/MAF) pair and a delayed decision filter/embedded median trimmed filter (DDF/EMTF) pair. Median filters and median-related filter cause an edge shift in the presence of an impulse near the edge. The proposed filters reduce such edge shifting while suppressing impulsive as well as nonimpulsive noise. It is shown that at the noisy edge point the NMF and the DDF are substantially superior both theoretically and experimentally to the median filter, the α-TM filter, and the STM filter in two respects: (1) the output bias error and (2) the output mean square error. It is also shown that in the noisy homogeneous region (nonedge point), the bias errors of the MAF are zero and the output mean square errors of the MAF are substantially close to those of the optimized single-level filters: the averager, the median filter, and the min-max filter under Gaussian, Laplacian, and uniform noise, respectively. Test results confirm that the NMF/MAF pair and the DDF/EMTF structure are each robust in preserving sharp edges, inhibiting edge shifting, and suppressing a wide variety of noise     

A summary, by illustrations, of least-squares filters with constraints

Several methods of combining a number of time series into a single series are discussed. They are all individual filtering followed by summation and are somewhat like Wiener filtering in that a least-squares criterion is used to design the filter coefficients. They differ from Wiener filtering in that signal information is given in the form of various constraints on the filter coefficients rather than being given as a signal correlation function. The equations are worked out explicitly for the case of two time series and three filter points and presented in such a way as to make generalization clear.     

全集成连续时间跨导电容滤波器的进展

过去１０多年来，全集成连续时间跨导电容（ＯＴＡ－Ｃ）滤波器已成为一类重要的滤波器电路。本文回顾了它的发展历史，综述了这一领域内的进展，指出了有待研究的有关课题。     

Multirate digital filters, filter banks, polyphase networks, andapplications: a tutorial

The basic concepts and building blocks in multirate digital signal processing (DSP), including the digital polyphase representation, are reviewed. Recent progress, as reported by several authors in this area, is discussed. Several applications are described, including subband coding of waveforms, voice privacy systems, integral and fractional sampling rate conversion (such as in digital audio), digital crossover networks, and multirate coding of narrowband filter coefficients. The M-band quadrature mirror filter (QMF) bank is discussed in considerable detail, including an analysis of various errors and imperfections. Recent techniques for perfect signal reconstruction in such systems are reviewed. The connection between QMF banks and other related topics, such as block digital filtering and periodically time-varying systems, is examined in a pseudo-circulant-matrix framework. Unconventional applications of the polyphase concept are discussed     

Nonlinear modeling and processing of speech based on sums of AM-FMformant models

We describe a new statistical approach based on nonlinear filtering ideas for decomposing signals that are modeled as a sum of jointly amplitude- and frequency-modulated cosines, where each cosine has a slowly varying center frequency and the sum of terms is observed in additive noise. This is an alternative approach to methods based on deterministic models such as the Kaiser-Teager (see Proc. IEEE ICASSP-93, vol.III, p.149 and IEEE Trans. Acoust., Speech, Signal Processing, vol.28, no.5, pp. 599, 1980) energy operator. The Cramer-Rao bound for the resulting statistical estimation problem is computed. A practical nonlinear filter, an extended Kalman filter, is described. We demonstrate the ideas on a variety of speech problems     

Characteristics of distributed Bragg reflector active optical filters

The transfer function characteristics of distributed-Bragg-reflector (DBR)-based active optical filters are described. Small and large signal characteristics are presented, and a variety of nonlinear effects obtained in the large signal regime such as gain saturation, frequency pulling, and wavelength domain bistability are demonstrated. While these nonlinear effects may be detrimental to conventional filter applications, they may possibly be explored for new approaches in wavelength domain logic, switching, and routing. The filter can also be used in a reversed configuration. Compared to the characteristics described, the small signal transmission transfer function remains unchanged but the input power at which the nonlinear effects take place is increased by 20-30 dB. This is due to the much reduced reflected power inside the filter cavity. At the same time, however, the noise power added to the amplified signal is also significantly increased.<>