共查询到19条相似文献,搜索用时 140 毫秒
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当前应用在带钢表面缺陷图像的基于单个系数点的融合规则和基于区域系数特征的融合规则存在片面性、容易使融合图像失真等问题.针对以上问题,给出了一种新的融合规则.该融合规则在对小波分解后的高频子带进行融合时,充分考虑待融合图像的局域方差的相异度,并利用阈值来选择合适的融合规则.实验结果表明,该方法可以更好地保留图像的细节特征,且在冷轧带钢表面缺陷图像融合中有较好的适用性,具有一定的工程应用价值. 相似文献
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小波在分析流态化系统多尺度动态行为中的应用 总被引:5,自引:0,他引:5
利用小波分解方法,对用激光相位多普勒颗粒分析仪(PDPA)、光纤探针及压差传感器同时测得的二维循环流化床中的信号进行了分解,并对分解信号和三种原始信号进行了比较。研究表明:将动态过程分解为三种尺度是合理的,PDPA信号包含了循环流化床所有尺度的全部信息。分解后三种尺度信号均具有混沌性态,但可预测性比原始信号好,为增加对动态过程的认知和建立较好的动态表达模型提供了途径。 相似文献
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为了更准确、方便地估算闪烁背景光下的LCD液晶响应时间,利用小波变换法对测量得到的LCD亮度响应曲线进行滤波.通过实际测量连续背景光下五级灰度之间的液晶响应以及闪烁背景光的背景光响应,构造了闪烁背景光下的LCD亮度响应,利用小波变换滤波方法,通过小波分解、阈值处理、逆变换重构,还原了液晶响应信号,将估算得到的响应时间与真实值以及移动窗口积分方法的估算值进行比较.根据计算,移动窗口积分法的平均估算误差为7.535 5%,而小波变换滤波法的平均估算误差仅为1.966 5%.结果表明,小波变换滤波法对闪烁背景光技术下LCD液晶响应时间的估计比移动窗口积分法更加准确,而且应用简单,适应面广. 相似文献
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为识别钢筋混凝土简支梁的损伤状况,对简支梁进行了逐级加载实验,每级加荷后卸荷,观测梁的裂缝,并测定梁的动力反应.将钢筋混凝土简支梁作为无限自由度体系,并对该体系的动力方程进行小波变换,得到多尺度下的结构动力响应表达式.信号经多尺度分解后,包含了信号中更多的结构损伤信息.基于此,用DASP信号处理系统对钢筋混凝土简支梁各损伤阶段的动态信号进行二进制小波分解,通过分析各频段的波形,确定了梁的损伤. 相似文献
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Wall clutter filters used in Doppler ultrasound systems give rise to a bias in the mean frequency estimation. This effect has been explored for two second order filters: the initialised infinite impulse response (IIR)-type filter, and the finite impulse response (FIR) echo-canceller filter. These are used in conjunction with two mean frequency estimation algorithms: the FFT-based intensity-weighted-mean algorithm, and the autocorrelation algorithm. The bias is shown to be caused by the finite settling times of the filters. The IIR filter, although having a much better frequency response than the FIR filter, has a greater bias associated with it. A compromise between bias and frequency response is suggested and a simple method of bias correction is described. 相似文献
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针对一类具有空间不均匀性的辨识和回归问题,提出了基于小波分析的极限学习机方法.从多分辨率分析的思想出发,构造一簇紧支撑正交小波作为隐层激活函数,并利用改进的误差最小化极限学习机训练输出层权重,避免了新加入高分辨率子网络后的重新训练.同时,由一维多分辨分析的张量积构造了二维多分辨小波极限学习机.进而通过脊波变换将小波学习机扩展到高维空间,对脊波函数的伸缩、方向和位置参数进行优化计算.对具有奇异性的函数仿真结果证明,与标准极限学习机相比,小波极限学习机由于其聚微性能在极短的训练时间内更好地逼近目标.一些实际基准回归问题上的测试验证了脊波极限学习机在其中大部分问题上达到更高的训练和泛化精度. 相似文献
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This paper develops a new representation scheme for random fields, which can be used in a variety of mechanics applications, based upon the projection onto a biorthogonal wavelet basis. The merits of such a scheme can be shown to result from the relaxation of the condition of orthonormality, while still requiring compact support of the basis functions. Earlier methods have relied on the diagonalization properties of wavelets to demonstrate how the Daubechies family of orthonormal wavelets is effective in weakening the correlation across scales for a large class of random processes. It is shown that biorthogonal processes achieve better decorrelation owing to the fact that fewer filter coefficients are needed to maintain the same support of basis functions when compared to the Daubechies family. Numerical examples of fields encountered in earthquake engineering and other applications are given. 相似文献
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Multiresolution methods are reported for feature extraction in breast cancer screening using digital mammography. The initial application is directed at the detection of microcalcification clusters (MCCs). Quadrature mirror filter (QMF) banks, using both two and three channel are proposed for the first time for both multiresolution decomposition and reconstruction. These filters are specifically tailored for automatic extraction of MCCs. The QMF multiresolution methods are compared to two channel tree structured wavelet transforms (TSWTs) methods previously reported. The QMF filters are preceded by an advanced tree structured nonlinear filter for noise suppression, prior to feature extraction, in order to minimize the false positive (FP) detection rate in digital mammography. The relative performance of these methods were evaluated using both simulated images and fifteen representative digitized mammograms containing biopsy proven microcalcification clusters. Similar high sensitivity (true positive (TP) detection rate (100%) and high specificity (0.6 average false positive (FP) MCC's/image) were observed, substantially better than more traditional approaches using single scale filters. The three channel QMF method, however, demonstrated better detail preservation of MCC's extracted compared to the two channel method. Detail preservation is important for the characterization of MCC's or individual microcalcifications in cancer screening. 相似文献
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Wavelet-Based Approach for Structural Damage Detection 总被引:1,自引:0,他引:1
A wavelet-based approach is proposed for structural damage detection and health monitoring. Characteristics of representative vibration signals under the wavelet transformation are examined. The methodology is then applied to simulation data generated from a simple structural model subjected to a harmonic excitation. The model consists of multiple breakable springs, some of which may suffer irreversible damage when the response exceeds a threshold value or the number of cycles of motion is accumulated beyond their fatigue life. In cases of either abrupt or accumulative damages, occurrence of damage and the moment when it occurs can be clearly determined in the details of the wavelet decomposition of these data. Similar results are observed for the real acceleration data of the seismic response recorded on the roof of a building during the 1971 San Fernando earthquake. Effects of noise intensity and damage severity are investigated and presented by a detectability map. Results show the great promise of the wavelet approach for damage detection and structural health monitoring. 相似文献
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We propose two original methods of denoising of the uterine electrohysterography (EHG) signal by wavelets. This external electrophysiological signal is corrupted by electronic, electromagnetic noises and by the remaining electrocardiogram of the mother. The interfering signals have overlapping spectra. Therefore, a classical filtering is unusable. Wavelets should be a very well-suited denoising tool. The first proposed method uses the algorithm "à trou" with nonsymmetrical filters. The computation is rapid and the results are satisfying compared to the classical denoising techniques. The second algorithm is an improvement of the first method. It uses orthogonal wavelets and the result of the thresholding corresponds to the average of all circulant shifts denoised by a decimated wavelet transform. Results are compared to traditional denoising algorithms by wavelet (orthogonal, maximally decimated). The proposed algorithms are more efficient on simulated signals as well as on uterine EHG. 相似文献
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We are developing a computer-aided diagnosis (CAD) scheme for detection of clustered microcalcifications in digital mammograms. The use of an empirically chosen wavelet and scale combination for detection of microcalcifications as an initial step of the CAD scheme has been reported by us previously. In this study, we developed a technique for optimizing the weights at individual scales in the wavelet transform to improve the performance of our CAD scheme based on the supervised learning method. In the learning process, an error function was formulated to represent the difference between a desired output and the reconstructed image obtained from weighted wavelet coefficients for a given mammogram. The error function was then minimized by modifying the weights for wavelet coefficients by means of a conjugate gradient algorithm. The Least Asymmetric Daubechies' wavelets were optimized with 297 regions of interest (ROIs) as a training set by a jackknife method. The performance of the optimally weighted wavelets was evaluated by means of receiver-operating characteristic (ROC) analysis by use of the above set of ROIs. The analysis yielded an average area under the ROC curve of 0.92, which outperforms the difference-image technique used in our existing CAD scheme, as well as the partial reconstruction method used in our previous study. 相似文献