Filtering algorithm for noise reduction in phase-map images with 2pi phase jumps

A filtering algorithm is proposed for processing images generated by TV holography that contain phase jumps and a high noise level. This algorithm first performs phase unwrapping without removing the noise. After that, it removes the noise by use of a conventional low-pass filter. The new approach allows for using low-pass filters with narrow passbands, leading to a better signal-to-noise ratio in the desired signal. Simulation results are presented and discussed. The new algorithm has been applied successfully under real conditions in a holographic station.     

New spin filters for interferometric fringe patterns and grating patterns

The basic spin filter for interferometric fringe patterns is improved and developed into several new versions for different applications. These spin filters can filter off random noise efficiently and have almost no blurring effect and phase distortion for the fringe patterns. First, they find the local fringe tangent direction, and then they apply a one-dimensional low-pass filter on this direction. In this way the spin filters can separate easily and clearly high-frequency noise from a real fringe signal with nearly zero frequency. The new spin filters are suitable not only for various fringe patterns but also for wrapped-phase, line-grating, and cross-grating patterns, which are impossible by common filters.     

Study and Performance Evaluation of Two Iterative Frequency-Domain Deconvolution Techniques

The performance of two iterative frequency-domain deconvolution techniques, the optimum compensation and the Guillaume-Nahman, is evaluated. The study involved the characterization of the adaptive filters utilized to reduce the deconvolution noise. Comparisons between the two techniques are performed for various classes of signals having different levels of acquisition noise. It is found that the Guillaume-Nahman technique is potentially more accurate but more sensitive to acquisition noise. It is also found that the optimum compensation deconvolution technique uses an adaptive filtet with the passbands coinciding with the frequency bands of the signal, thus optimizing noise filtration, while the Guillaume-Nahman technique utilizes a low-pass filter for all signals.     

Envelope signal selective emphasis in a polar radio frequency transmitter architecture

The linearity of an efficient polar transmitter architecture, with a 1 bit oversampled delta?sigma (DS) modulating the envelope signal, depends, to a high degree, on low-pass envelope filtering. This filter is compulsory to attenuate the DS quantisation noise. A high cut-off frequency results in more noise being included. In contrast, using a filter with a low cut-off frequency results in attenuation of the information content of the envelope signal. Either way, the result is unwanted spectral regrowth. By pre-emphasising the envelope signal, the filter?s attenuation of the information is mitigated. The pre-emphasis is implemented by a digital pseudo-derivative high-pass filter, with inverse magnitude characteristics of the analogue low-pass filter, within a limited interest band. Consequently, the low-pass filter can be designed with a lower cut-off frequency to attenuate more of the DS modulator noise, and the modulator can switch at lower frequencies. With this technique, the WLAN output spectrum, at the critical 30 MHz offset corner frequency, is improved by 12.5 dB, considering a second order DS sampling at 1.28 GHz. The technique was verified with an experimental setup and the behaviour agrees well with simulations.     

剑杆织机前馈-反馈张力控制系统的分析与设计

在分析剑杆织机张力控制中噪声源及噪声特性的基础上,提出控制结构和控制器的设计方法,选择合适的模拟低通滤波器,对检测通道的高频振动信号和随机噪声进行滤波.针对周期性低频振动噪声,一方面,采用频谱分析定周期+相干平均法定信号的方法估计模拟低通滤波器后的周期性振动噪声,并在反馈通道进行补偿,提高控制性能;另一方面,采用频谱分...     

Adjustable active optical low-pass filter

This paper presents an active optical low-pass filter (AOLPF) capable of changing the resolution of an imaging system on demand in order to remove aliasing noise from a sampling image. This is advantageous over conventional optical low-pass filters, which are fixed image-blurring optical components that are built into the imaging system, in order to remove aliasing in the image. Furthermore, conventional filters smear images regardless of the presence or lack of high spatial frequency, which can exceed the Nyquist limit of the sensor. On the contrary, the proposed AOLPF can dynamically adjust the modulation transfer function of an imaging system to eliminate aliasing artifacts. In addition, this filter can be turned off in the absence of high spatial frequency to maximize resolution and prevent unnecessary blurring of the sampling image.     

基于二阶Butterworth低通滤波器的磁控埋弧焊滤波新方法

介绍了一种新的磁控埋弧焊接电弧信号滤波方法,即二级Butterworth低通滤波法,并将其滤波效果与传统的简单低通滤波方法和软件中值滤波方法进行比较。结果表明:采用二级Butterworth低通滤波器对磁控埋弧焊试验中的输出焊接电弧波形进行滤波,不仅可以滤掉无用的噪声信号,而且能够很好地保留原始输出电弧波形中反映电弧位置的特征信息,其滤波效果优于传统的简单低通滤波法和软件中值滤波法,可以很好地满足不断提高的焊接质量要求。     

Comparison of the efficiency of averaging the signal from multicomponent force trans-ducers by direct and discrete methods

The efficiency of the direct method of averaging the output signal from multicomponent force transducers with filters is considered. A single-stage oscillatory system, acted on by random load fluctuations, is taken as a dynamic model of a transducer. The averaging filters are a Hanning integrator and filter. The dependences of the filter base on the averaging time are determined as is the influence of the sampling frequency on the discrepancy between the characteristics obtained using discrete and continuous methods of signal averaging. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 26–28, July, 1997.     

Comparative analysis of low-pass filters for the demodulation ofprojected gratings in 3-D adaptive profilometry

In 3-D adaptive profilometry based on structured light projection, the choice of the low-pass filter to he used in the deformed pattern demodulation is crucial. In this paper, we have studied the performance of a typical finite impulse response (FIR) and of an infinite impulse response (IIR) Butterworth low-pass filter. Adaptiveness of the filters to both coarse and small variations of the grating frequency has been investigated. The ability of the filters to adapt to coarse changes of the grating frequency has been quantified in terms of their speed of synthesis, while the ability of the filters to tolerate small variations of the grating frequency has been quantified by measuring the residual phase errors. The analysis shows that the IIR Butterworth filter performs better than the FIR filter both in the coarse and in the fine grating frequency variation cases     

Improved optimization of soft-partition-weighted-sum filters and their application to image restoration

Soft-partition-weighted-sum (Soft-PWS) filters are a class of spatially adaptive moving-window filters for signal and image restoration. Their performance is shown to be promising. However, optimization of the Soft-PWS filters has received only limited attention. Earlier work focused on a stochastic-gradient method that is computationally prohibitive in many applications. We describe a novel radial basis function interpretation of the Soft-PWS filters and present an efficient optimization procedure. We apply the filters to the problem of noise reduction. The experimental results show that the Soft-PWS filter outperforms the standard partition-weighted-sum filter and the Wiener filter.     

FRM滤波器中应用积分梳状滤波器的研究

传统的频率响应屏蔽(Frequency Response Masking,FRM)滤波器由多个含有乘法器的滤波器构成,计算复杂度较高。提出了一种改进窄带低通FRM数字滤波器设计复杂度的方法,使用积分梳状滤波器作为屏蔽滤波器,以达到设计窄过渡带的滤波器的要求。仿真结果表明,在降低窄带低通FRM滤波器计算复杂度方面效果明显,有效地减少了乘法器的使用,降低了目标滤波器设计的阶数。该方法可以应用于窄过渡FRM数字滤波器的设计中。     

参数扰动的RLC低通滤波器的随机共振

研究了RLC低通滤波器在电导受到非对称双值色噪声扰动时的随机共振现象．利用随机平均法和Shapiro—Loginov公式,得到了平均输出幅度增益的精确表达式．分析表明,在欠阻尼、临界阻尼和过阻尼RLC低通滤波器中,平均输出幅度增益对电导噪声的非对称性、相关时间、强度和信号频率都存在非单调依赖关系．适当的噪声和系统参数条件可以使有噪声时系统的平均输出幅度增益大于没有噪声时系统的平均输出幅度增益．噪声可以提高滤波器对高频信号的衰减率．恰当的条件可以获得平均输出幅度增益的最大值．     

谐振式光纤陀螺的数字检测方案及其优化设计

提出了一种基于 DSP 芯片实现的双频率数字调制谐振式光纤陀螺系统的闭环检测方案。在此方案中,利用带通滤波器从探测器的输出光强信号中提取其基波频率的正弦信号,通过相关检测原理去掉干扰的噪声,并利用低通滤波器提取与探测器输出光强幅度直接成正比的直流信号,将其转换成相应的谐振频差,利用此频差即可求得陀螺的旋转角速度。此方案检测线路简单,操作方便,基于 DSP 芯片的实现则大大提高了系统处理速度。同时,还利用 Matlab 软件对检测系统中的滤波器参数进行了优化设计,提高了系统的检测精度。     

Effect of Spectrum on the Measurement of Noise

A substantial discrepancy was found to exist between the sigma (standard deviation) of the noise present in radar data as determined by subtraction of data smoothed by a low-pass filter from the raw data and use of successive differences to isolate the noise. An investigation revealed that implicit in the equation based on the successive differences approach was the assumption that the noise was white, bandlimited, and with a cutoff frequency equal to the Shannon frequency. Hence, analyses were performed to take into account other situations, namely: band-limited white noise having a cutoff frequency less than the Shannon frequency; white noise modified by an RC filter; and spurious sinusoidal signal present. By taking into account these various types of noise spectra, it was possible to obtain excellent agreement between the two methods for measuring the noise sigmas.     

Hybrid order statistic filter and its application to image restoration

We introduce a new nonlinear filter for signal and image restoration, the hybrid order statistic (HOS) filter. Because it exploits both rank- and spatial-order information, the HOS realizes the advantages of nonlinear filters in edge preservation and reduction of impulsive noise components while retaining the ability of the linear filter to suppress Gaussian noise. We show that the HOS filter exhibits improved performance over both the linear Wiener and the nonlinear L filters in reducing mean-squared error in the presence of contaminated Gaussian noise. In many cases it also performs favorably compared with the Ll and rank-conditioned rank selection filters.     

去除脉冲噪声的自适应开关中值滤波

为消除图像中的脉冲噪声,提出了自适应开关中值(ASM)滤波算法。该算法采用一种新的噪声检测方法将图像中的像素分为信号点和噪声点两类。对检测出的噪声点统计其个数并由此估算图像中的噪声密度,根据估计的噪声密度自适应确定滤波窗口尺寸,采用改进的中值滤波对检测出的噪声点进行处理;而信号点则保留其灰度值不予处理。对ASM滤波进行仿真实验,结果表明,它能在有效去除噪声的同时很好地保护图像细节,较传统中值滤波及其它改进中值滤波算法有更优的滤波性能。     

Moire fringe reduction by optical filters in integral three-dimensional imaging on a color flat-panel display

We propose a method to reduce the color moire fringes that are attributable to the structure of a color flat-panel display in integral three-dimensional imaging. The method uses two types of optical low-pass filter, diffuser and defocus. The effectiveness of the method was confirmed in an experiment. We describe a way to design these filters with moire's residual energy and video signal energy as indices and demonstrate the validity of the model, which combines two filters to reduce moire fringes.     

Frequency stability characterization from the filtered signal of aprecision oscillator in the presence of additive noise

The authors present a generalized theory to express the frequency stability characterization of a precision oscillator when its signal, perturbed by additive noise, is filtered. The general expressions for the power spectral density of the amplitude and phase fluctuations of the filtered signal are calculated as functions of the oscillator amplitude and phase fluctuations, the additive noise, and the filter characteristics. The results obtained for the phase fluctuations of the filtered signal are used to characterize the frequency stability of the oscillator. The contribution of white additive noise to the generalized Allan variance is expressed in terms of a parameter, the equivalent bandwidth. The contributions of other types of noise are also calculated. For the first-order low-pass filter, the contributions of all types of additive, amplitude, phase, and frequency noise are given. Experimental results show excellent agreement with the theoretical predictions     

Visual signal detection with two-component noise: low-pass spectrum effects

Detection of signals in natural images and scenes is limited by both noise and structure. The purpose of this study is to investigate phenomenological issues of signal detection in two-component noise. One component had a broadband (white) spectrum designed to simulate image noise. The other component was filtered to simulate two classes of low-pass background structure spectra: Gaussian-filtered noise and power-law noise. Measurements of human and model observer performance are reported for several aperiodic signals and both classes of background spectra. Human results are compared with two classes of observer models and are fitted very well by suboptimal prewhitening matched filter models. The nonprewhitening model with an eye filter does not agree with human results when background-noise-component power spectrum bandwidths are less than signal energy bandwidths.     

Digital-to-analog conversion by pulse-count modulation methods

Three low-cost digital-to-analog converters (DACs) are described and compared. These designs can easily be implemented in an integrated circuit: the conventional pulse-width modulation (PWM) DAC, the new pulse-count modulation (PCM) DAC and the first-order noise shaping (FONS) DAC. All three methods control the ratio of the sum of all pulse durations to the constant total period. As the pulse durations are integral multiples of a unit pulse, all three can be classified as pulse-count modulation methods. Block diagrams of all three DACs consisting of a simple digital circuit and a low-pass filter are presented. For a constant digital input value the worst case ripple of the filter output is used to calculate the cutoff frequency of the low-pass filter. Approximations for the 3 dB cutoff frequency of first-order, second-order and fourth-order Butterworth low-pass filters are given. The dynamic properties are analyzed in the time domain (settling time) and in the frequency domain (unfiltered output spectrum of a full-scale sine wave input). The main influences on the static accuracy are analyzed. A case study demonstrates the abilities of PCM and FONS