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建立了超声探测缺陷回波的数学模型,讨论了信号奇异性同其小波变换之间的关系以及通过小波变换模极大值精确重构原信号的原理和方法,利用Mallat的交替投影算法对仿真的超声信号进行了精确重构和对实际检测到的超声信号进行了消噪处理。结果表明,利用小波变换模极大值重构信号的交替投影算法来重构超声信号,重构精度高,实现速度快,用于处理染噪信号,消噪效果好,是一种较为理想的处理超声信号的方法。 相似文献
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逆向工程是目前非常实用的一种新产品开发技术,而模型重构则是逆向工程中非常重要的内容,同时也是难点之一。将VC++6.0与UG二次开发相结合,首先通过投影法获取不同截面轮廓数据,然后对各轮廓数据进行数据预处理并实现排序,再进行曲线拟舍得到截面轮廓曲线族,最后实现三维模型重构。实验结果表明可以获得有效的产品重构模型。 相似文献
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研究了有限角 CT重构压缩算法中有限角度和投影幅数对重构结果的影响 .通过仿真程序 ,对不同的有限角度和投影幅数下的压缩重构结果进行分析和比较 ,得出不同的有限角度和投影幅数下重构质量有很大的不同 .当缺失角大于等于 3 0°时 ,重构质量很差 .说明压缩算法其本身具有较大的局限性 相似文献
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针对固定电极的电容层析成像技术独立测量值较少,且由于电极位置的影响而导致重建图像失真等问题,提出了一种基于16旋转电极的电容层析成像技术系统模型及对应的图像融合方法。模型对16电极的电容层析成像技术模型进行4次旋转,得出的数据分别采用线性反投影算法和修正共轭梯度法算法进行图像重建,再将重建的5张图像进行小波变换,变换得到的低频和高频成分分别采用加权平均和主分量分析的融合准则进行图像融合。实验结果表明:提出的电容层析成像技术旋转模型通过增加测量电容数,结合图像融合方法可明显提高重构图像质量,降低成像误差。 相似文献
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采用超声△衍射法和TOFD法对模拟缺陷进行检测,得出了缺陷检测波形图和B/C扫描图.对比分析了超声△衍射法与TOFD法的检测结果.实验表明利用超声△衍射法能够识别近表面垂直表面的面状缺陷,有效地对缺陷进行定位,能够很好地克服表面盲区,对缺陷的检测识别能力不受缺陷方向限制.从检测结果数据可以看出超声△衍射法的检测灵敏度和缺陷识别能力优于TOFD法. 相似文献
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赵志丹 《现代测量与实验室管理》2004,12(6):33-36
用实验的方法对紧凑型荧光灯各光电参数和色参数在不同的条件下相对变化的分析和研究,为建立紧凑型荧光灯的国家标准以及确定相应的测试方法提供了重要的依据。本文根据大量的实验数据绘出相应的变化曲线,直观地表达了紧凑型荧光灯各参数在不同的实验条件下的一系列相对变化,并对这些曲线作了简要的定性分析;从这些数据中得出相应的经验公式。 相似文献
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Lifeng Yu Xiaochuan Pan Charles A. Pelizzari 《International journal of imaging systems and technology》2004,14(5):213-221
It is well known that cone‐beam data acquired with a circular orbit are insufficient for exact image reconstruction. Despite this, because a cone‐beam scanning configuration with a circular orbit is easy to implement in practice, it has been widely employed for data acquisition in, e.g., micro‐CT and CT imaging in radiation therapy. The algorithm developed by Feldkamp, Davis, and Kress (FDK) and its modifications, such as the Tent–FDK (T‐FDK) algorithm, have been used for image reconstruction from circular cone‐beam data. In this work, we present an algorithm with spatially shift‐variant filtration for image reconstruction in circular cone‐beam CT. We performed computer‐simulation studies to compare the proposed and existing algorithms. Numerical results in these studies demonstrated that the proposed algorithm has resolution properties comparable to, and noise properties better than, the FDK algorithm. As compared to the T‐FDK algorithm, our proposed algorithm reconstructs images with an improved in‐plane spatial resolution. © 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 14, 213–221, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20026 相似文献
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文中提出了宽带合成孔径声纳(synthetic aperture Sonar,简称SAS)成像的反向投影算法(back pmjection,简称BP)。该算法是在时间-空间域中对合成孔径线列阵中备个阵元接收回波的所有频率分量进行相干求和,以充分利用合成孔径上所有回波的能量,从而得到理想的SAS图像。同时,文章中分析了BP算法实现过程中拖尾(tall)现象的产生机理,对BP重建图像进行了斜坡滤波处理。并对载频为15kHz,带宽为20kHz的SAS系统进行了仿真,结果验证了这种算法的有效性。 相似文献
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There are some compelling reasons for viewing the problem of image reconstruction from noisy or incomplete data as one of statistical estimation, i.e., of choosing, from the infinity of images consistent with the data, that image which, in some statistical sense, is most plausible. Among these reasons are the soundness of the philosophical underpinning of the resulting image reconstruction process, a greater realization of the image resolution which is inherent in the data, and freedom from many of the artifacts encountered in commonly used ad hoc reconstruction schemes. One successful technique employing a principle of statistical inference is the maximum entropy technique, in which the data-consistent image with maximum configurational entropy is chosen. It is a computationally intensive approach involving a conjugate gradient search over a convex function of a vector in a space of dimensionality equal to the number of image pixels. This technique has been employed with success in situations where the data samples are modeled as linearly related to a real non-negative object. We investigate application of maximum entropy image reconstruction to the problem of high-resolution radar diagnostic imaging. The problem differs from others in which maximum entropy has been applied in that the object to be imaged is complex. Although the desired image is of the magnitude of the complex object and is thus real and non-negative, there is no linear relationship beween object magnitude and data. Rather, the data are linearly related to the complex object. Several earlier proposed methods for applying the maximum entropy principle to this problem are identified and analyzed. A method that more closely approximates true Bayesian estimation is proposed. 相似文献
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《成像科学杂志》2013,61(6):503-508
AbstractSingle-photon emission computerised tomography (SPECT) and positron emission tomography (PET) are essential medical imaging tools, with inherent drawback of slow data acquisition process. We present a novel compressed sensing-based reconstruction of these images from significantly fewer measurements than traditionally required, thus demonstrating potential of reduction in scan time and radiopharmaceutical doze with benefits for patients and health care economics. Our work effectively shows that high fidelity two-dimensional (2D) SPECT/PET image is reconstructed using compressive sensing with considerably reduced numbers of samples in acquisition stage. The reconstruction of tomographic images is realised by compressed sensing the 2D Fourier projections of k-space data. These 2D projections being sparse in transform domain need fewer samples in k-space and are reconstructed without loss of fidelity. These undersampled Fourier projections can then be backprojected by employing the iterative reconstruction approach for a complete three-dimensional (3D) volume. Compressed sensing of a phantom image and PET bone scintigraphy with radial Fourier samples are performed. The reconstructions of these images are compared to conventionally sampled images using image quality measures like mean square error, peak signal-to-noise ratio and structure similarity (SSIM) index, showing high-quality image reconstruction. 相似文献
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In this paper we give theoretical analysis of an image formation and reconstruction of individual islands of nano-size dimensions in the coherent GISAXS experiments. It is shown that there are some favorable conditions with incident angle close to the critical angle when GISAXS diffraction patterns originating from the individual islands can be directly inverted using iterative phase retrieval techniques. 相似文献
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为解决两相流中存在中心物体、物体比较小或存在多个物体且相距较近时电容层析成像(ECT)重建图像精度较差的问题,基于稀疏分布的流型其介电常数分布满足稀疏性的先验条件,采用梯度投影稀疏重建(GPSR-BB)算法进行ECT图像重建。仿真及实验测试结果表明:GPSR-BB算法对于流体中小目标以及复杂流型的图像重建质量较好,重建图像的形状保真度高。 相似文献