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1.
滤波反投影算法是解析法图像重建的经典算法,其加速方法的研究是目前研究的热点之一. 利用算术傅里叶变换和分段卷积的组合可实现滤波加速的方法:首先将斜变滤波器的单位冲激响应分为两段,然后每一段与投影信号采用算术傅里叶变换的方法间接实现线性卷积,最后利用重叠相加法求得滤波投影.实验表明,此方法可以有效地提高滤波反投影算法的运算速度,可比直接卷积的运算速度快390倍,比采用快速傅里叶变换方法的速度快约30%,是一种有效的加速方法.  相似文献   

2.
采用冲击回波法检测混凝土厚度或者缺陷时,采用传统快速傅里叶变换方法,由于傅里叶变换的时移性以及信号中包含表面波和结构模态振动使得特征频率的提取较为困难。要解决特征频率提取受到干扰的问题,该文提出一种小波变换结合傅里叶变换的信号处理方法。首先对回波信号进行小波变换,得到信号时频图和小波边际谱,其次将小波边际谱与傅里叶谱相乘,得到增强傅里叶谱。结果表明:信号时频图可以确定表面波和模态振动的频率范围和时间跨度,增强傅里叶谱不仅可保证频率分辨率,而且抑制由于傅里叶变换的时移性产生的多个波峰,使得特征频率在频谱中更为清晰和准确,是一种适用于冲击回波检测的信号处理方法。  相似文献   

3.
针对主轴运行过程中突加不平衡而产生的非平稳信号无法采用传统的傅里叶变换对信号进行分析处理的问题,提出一种采用小波降噪与短时傅里叶变换相结合对主轴振动特征信息进行准确提取的方法,该方法利用小波降噪技术对非平稳信号进行滤波处理,再对滤波处理后的信号进行重构,最后通过短时傅里叶变换精确获取主轴振动幅值,通过仿真和实验验证了该方法的有效性。  相似文献   

4.
针对往复机械振动信号具有复杂非线性、非平稳等特性,使用一种基于小波框架的自适应经验小波变换和以集合角度处理信号的形态学滤波来进行往复机械故障特征提取。首先使用自适应经验小波变换通过构造尺度空间曲线对傅里叶频谱进行划分,构造合适的正交小波滤波器组以提取具有紧支撑傅里叶频谱的AM-FM成分;然后根据往复机械振动信号冲击性的特点,基于信号本身特性构造形态学结构元素,对提取出的模态进行状态自适应形态学滤波;最后使用多尺度模糊熵对模态进行定量分析并对故障进行识别。将该方法应用到实测数据中,实验结果验证了该方法的有效性,该方法可以准确对往复压缩机气阀故障进行识别。  相似文献   

5.
牛成亮  蒋超猛  龚伟 《硅谷》2011,(14):168-168
基于matlab强大的数值计算功能,借助快速傅里叶变换,建立一个函数的快速傅里叶变换和逆变换的模型,并进行运行和分析,实现快速傅里叶变换在信号处理方面的强大而简捷的功能。傅里叶分析就是我们测量出复杂波形,然后寻求确定其中有哪些频率成分。确定一个已知波形的频谱的过程。快速傅里叶变换是一种计算机算法,它从计算机采集到的数据中计算频谱。用快速傅里叶分析可以把复杂信号分解成简谐信号之和,看到信号的本质。  相似文献   

6.
采用小波多分辨分析和快速傅里叶变换,对焊接裂纹金属磁记忆信号进行了处理,找出了焊接裂纹存在的磁记忆信号的判据特征,并建立了该特征的阈值.现场检测结果表明:采用小波多分辨分析和快速傅里叶变换得出的特征,可以准确判断出裂纹等缺陷是否存在.  相似文献   

7.
本文首先利用双向测量法测量原理,通过A/D转换器、由计算机控制对主轴回转误差进行数据采集、预处理与转换。以快速傅里叶变换为基础对回转误差信号进行功率谱分析,并提出以快速傅里叶变换和逆变换的方法对一次偏心分量进行消除。该系统运用于ZHS-1型多功能转台主轴回转精度的实际测量,实现了主轴回转误差的在线测量和实时分析处理。  相似文献   

8.
二维傅里叶变换法三维曲面检测   总被引:1,自引:0,他引:1  
对投影光栅方法获得的位相调制空间载波图进行二维数字图象处理,实现了散射物体的三维曲面测量,利用二维快速傅里嚅变换将空域信号转变为频域信号,对一级频谱进行傅里叶反变换,逐步解调出其位相值,重建了被测物体表面的形貌。文中给出了对人体模型的实验测量结果。  相似文献   

9.
郑海明  刘佳 《计量学报》2020,41(6):759-764
对差分吸收光谱测量臭氧浓度信号去噪进行了实验研究。首先利用常用的小波变换、Savitzky-Golay滤波和傅里叶变换滤波这3种方法对臭氧的吸收光谱分别进行去噪处理,得到各自去噪后的吸收光谱,发现小波变换与Savitzky-Golay滤波可以很好地拟合特征吸收,傅里叶变换滤波稍差;然后,利用信噪比与均方根误差对所得光谱进行分析评价。实验结果表明:Savitzky-Golay滤波对信号去噪的效果最好,可优先应用于臭氧的光谱计量分析。  相似文献   

10.
连续小波变换快速带通滤波实现算法的研究   总被引:4,自引:3,他引:1  
针对连续小波变换(Continuous wavelet transform,CWT)计算量较大的问题,提出了一种利用带通滤波实现CWT的快速算法.根据CWT的定义,可将某一尺度下的小波函数看作一带通滤波器的传递函数,于是对信号和小波函数分别进行采样后,再利用快速傅里叶变换实现两个序列的线性卷积,便能求出相应尺度下的小波系数.推导了任意尺度对应的频率与尺度、小波中心频率、信号采样频率、小波函数采样频率之间的关系式,并分析了算法的计算量.仿真和应用结果表明,该法速度很快,精度较高,并且尺度可以任意取值,非常适合于工程应用.  相似文献   

11.
基于部分相干成像和分数傅里叶变换理论,建立成像系统的分数傅里叶域滤波模型,提出了可快速设计分数域位相型滤波片的 FrPI 算法。此算法将逆向设计预设初位相与分数傅里叶迭代技术相结合,针对成像系统中不同的设计要求可快速设计出所需的分数域滤波片结构。模拟结果表明,对数值孔径有限的部分相干成像系统,使用新算法设计的分数域滤波片,可有效补偿由于高频损失带来的图像失真,从而使局部线宽偏差和面积偏差分别由滤波前的 36.548nm 和 39.09%下降到了 15.234nm 和 7.72%,明显减少了空间像畸变。  相似文献   

12.
A novel frequency domain excision filter for use in front of broadband adaptive beamformer systems is presented. The proposed frequency domain excision filter uses image processing techniques to determine the excision threshold such that only narrowband interference is removed from the received signal. By preexcising the received signal of narrowband interference the adaptive beamformer only has to remove partialband or broadband interferers. This frees up degrees of freedom (DoF) in the adaptive beamformer in mixed interference environments allowing for a greater interference suppression capability. The proposed preexcision system is simulated using a constrained space-time adaptive processor as well as a constrained suboptimal space-frequency adaptive processor. It is shown that when pre-excision is used in front of a beamformer the total number of interference sources that can be simultaneously rejected is increased as long as the beamformer's DoF are exceeded by narrowband interference.  相似文献   

13.
We propose what is to our knowledge a novel technique for filtering a two-dimensional multichannel color image based on its interpretation as a three-dimensional (3D) signal and the application of a 3D Fourier transform. The color image is considered to have the two usual spatial coordinates with the color distribution as the third dimension of the signal. This approach permits the 3D generalization of the usual phase-only filter and phase correlation, and color pattern recognition can be performed by means of a 3D correlation. We analyze two cases: whitening only along the color Fourier spectrum and whitening the whole 3D Fourier spectrum. We study the transformation induced in the color content of the image by the whitening of the color Fourier spectrum and how it affects the correlation distribution. In particular it is demonstrated that the whitening of the 3D Fourier spectrum improves the recognition performance of the correlation.  相似文献   

14.
计算机模拟的多普勒信号,可以为各种多普勒信号处理方法的研究提供信号源,从而了解各种不同处理方法的性能。本文提出的方法,运用白噪声通过一时变滤波器的原理,模拟产生平均频率,带宽和功能均随时间变化的多普勒信号。  相似文献   

15.
Yu FT  Lu G 《Applied optics》1994,33(23):5262-5270
We discuss the semicontinuous short-time Fourier transform (STFT) and the semicontinual wavelet transform (WT) with Fourier-domain processing, which is suitable for optical implementation. We also systematically analyze the selection of the window functions, especially those based on the biorthogonality and the orthogonality constraints for perfect signal reconstruction. We show that one of the best substitutions for the Gaussian function in the Fourier domain is a squared sinusoid function that can form a biorthogonal window function in the time domain. The merit of a biorthogonal window is that it could simplify the inverse STFT and the inverse WT. A couple of optical architectures based on Fourier-domain processing for the STFT and the WT, by which real-time signal processing can be realized, are proposed.  相似文献   

16.
用傅里叶相移特性估计位移   总被引:1,自引:0,他引:1  
提出了一种从频率域出发,估计出运动物体在空间域位移的算法。利用傅里叶变换的自配准性质和位移特性,用极坐标形式下连续图像相位谱的差直接估计运动目标的位移。与传统的寻找迪拉克峰值的方法相比,本方法无需重新变换回空间域,从而节省了处理时间,具有更好的实时性。实验证明,这种先求出相位谱的差,再用其周期数来估计位移的算法简单明了,其分辨能力不低于一个像素。该理论可以应用于图像跟踪和图像后期处理中。  相似文献   

17.
This paper presents a theoretical framework for performance characterization in strain estimation, which includes the effect of signal decorrelation, quantization errors due to the finite temporal sampling rate, and electronic noise. An upper bound on the performance of the strain estimator in elastography is obtained from a strain filter constructed using these limits. The strain filter is a term used to describe the nonlinear filtering process in the strain domain (due to the ultrasound system and signal processing parameters) that allows the elastographic depiction of a limited range of strains from the compressed tissue. The strain filter predicts the elastogram quality by specifying the elastographic signal-to-noise ratio (SNR(e)), sensitivity, and the strain dynamic range at a given resolution. The dynamic range is limited by decorrelation errors for large tissue strain values, and electronic noise for low strain values. Tradeoffs between different techniques used to enhance elastogram image quality may also be analyzed using the strain filter.  相似文献   

18.
马凯  王易川  陈喆  程玉胜 《声学技术》2020,39(6):769-773
针对强混响背景下经典的最小均方误差(Least Mean Square,LMS)滤波算法难以有效地实现信混分离的问题,提出一种基于分数阶傅里叶变换的自适应LMS算法。首先将混响信号和自适应LMS滤波算法中的参考信号进行分数阶傅里叶变换,寻找最优变换域,并在分数阶域进行带通滤波,然后将得到的信号进行分数阶傅里叶反变换,最后将基于正态分布曲线的变步长LMS算法应用于此混响条件下进行滤波。仿真和海试数据验证结果表明,在信混比为0 dB的情况下,算法仍可以有效地滤除混响,使信混比提高6dB。  相似文献   

19.
Graph filtering, which is founded on the theory of graph signal processing, is proved as a useful tool for image denoising. Most graph filtering methods focus on learning an ideal lowpass filter to remove noise, where clean images are restored from noisy ones by retaining the image components in low graph frequency bands. However, this lowpass filter has limited ability to separate the low-frequency noise from clean images such that it makes the denoising procedure less effective. To address this issue, we propose an adaptive weighted graph filtering (AWGF) method to replace the design of traditional ideal lowpass filter. In detail, we reassess the existing low-rank denoising method with adaptive regularizer learning (ARLLR) from the view of graph filtering. A shrinkage approach subsequently is presented on the graph frequency domain, where the components of noisy image are adaptively decreased in each band by calculating their component significances. As a result, it makes the proposed graph filtering more explainable and suitable for denoising. Meanwhile, we demonstrate a graph filter under the constraint of subspace representation is employed in the ARLLR method. Therefore, ARLLR can be treated as a special form of graph filtering. It not only enriches the theory of graph filtering, but also builds a bridge from the low-rank methods to the graph filtering methods. In the experiments, we perform the AWGF method with a graph filter generated by the classical graph Laplacian matrix. The results show our method can achieve a comparable denoising performance with several state-of-the-art denoising methods.  相似文献   

20.
《Journal of Modern Optics》2013,60(4):419-420
A novel approach to frequency multiplexing of images is presented. By modulating each image pixel at a different (temporal) frequency, the entire image can be transformed into an electrical signal utilizing a single detector. The electrical current of the detector is proportional to the spatial Fourier transform of the image, allowing one to perform spatial frequency manipulations in the time domain. The multiplexing is obtained by using a two-dimensional array of piezoelectric-elasto-optic modulators. By utilizing these effects one makes use of the mechanical resonance of the crystals simplifying the electrical signals needed for excitation. It is shown that a similar (or the same) modulator can be used for image reconstructions; i.e. performing the inverse Fourier transform. Preliminary results obtained with quartz crystals prove the feasibility of this approach.  相似文献   

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