第二代曲波变换的图像降噪新算法

Curvelet变换表示曲线奇异函数的异向性及图像边缘时,具有比小波变换更优的表示特性。针对小波图像降噪存在的不足,分析基于wrapping算法的快速离散曲波变换的特点,提出结合循环平移、厄尔迭代方法和蒙特卡洛阈值规则的新消噪方法。该算法充分利用曲波系数的相关性,消除了因Curvelet变换缺乏平移不变性引起的图像＂划痕＂失真和＂振铃＂效应。实验结果表明,该算法与传统的小波消噪、二代小波消噪、小波包消噪和曲波硬阈值消噪相比,得到降噪图像的峰值信噪比更高,视觉效果更好。     

图像小波阈值去噪中马赛克现象的处理

在图像去噪处理中，采用小波阈值去噪法会产生马赛克现象，造成图像失真．为此作者提出了利用指数函数处理小波系数的去噪方法，可以保证在与阈值去噪法获得同样信噪比条件下，减轻马赛克现象，并利用超声C扫描粘接检测图像验证了该算法的有效性．     

基于小波系数最优化阈值算法的研究

去噪问题是图像处理界研究的热门话题．利用小波变换技术滤除噪声则是图像去噪的有效手段之一．目的该领域内的研究主要集中在如何选取阈值以达到最好的去噪效果。本文在分析了背景和目标的特征后．提出了基于小波系数的最优阈值算法．该算法在有效保留了图像的边缘信息的同时．获得了较高的信噪比增益。     

自适应二进小波去噪法

本文通过引入一类新的可微阈值函数,建立了信号的能量同它的二进小波变换系数之间的关系.利用Stein无偏风险估计和梯度下降法,给出了迭代求解各尺度二进小波系数最优阈值的自适应去噪算法.数值实验结果表明,同现存的小波去噪技术相比,该算法的去噪结果具有更高的重构信噪比和更光滑的外观.     

采用离散余弦变换的小波图像去噪方法

提出一种通过对小波域中噪声能量的估计来进行去噪的新方法。算法采用离散余弦变换(DCT)提取小波系数的主要特征,无需对噪声方差进行估计。对图像进行小波分解,利用 DCT对高频子带进行局部特征提取;利用部分 DCT 系数对小波系数进行重建,并以重建系数的平均能量作为局部噪声能量的估计;去除原小波系数中的噪声分量后,进行小波逆变换,得到去噪后的图像。实验证明,其峰值信噪比(PSNR)比通常的阈值萎缩法提高了 2-4dB。     

小波去噪方法在管道应力波检测中的应用

介绍了一种适合于管道应力波检测的基于小波变换的去噪方法。利用小波变换多尺度分析的优点。根据有用信号和噪声在小波变换不同尺度下的传递特性的不同，进行小波系数阈值选取后，对剩余小波系数重建信号，得到有用信号的波形。结果表明，它能较好地抑制噪声，使信号的信噪比明显提高。     

一种采用多个小波基的图像融合去噪方法

提出了一种新的基于多个小波基的图像融合去噪方法.首先利用多个不同的小波基对含噪图像进行阈值去噪,得到多幅恢复图像.然后对这些图像采用小波融合方法进行融合.对于低频系数采用基于边缘的融合算法,在多幅恢复图像中选择最有可能是边缘的点加以保留;对于高频系数,采用了平均的融合算法.最后得到一幅去噪图像.实验结果表明,无论是在视觉效果上还是在峰值信噪比定量指标上该方法去噪效果均明显优于单一小波基去噪.     

差分吸收光谱测量臭氧浓度信号去噪的实验研究

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。     

基于波原子变换的三维地震信号盲去噪

基于波原子变换的三维地震信号盲去噪算法,利用基于块的噪声估计算法估计信号噪声,采用循环平移处理信号并进行波原子变换,利用估计的噪声标准差按不同尺度分层设置阈值并进行修正,再采用改进的阈值函数处理波原子变换系数,进行波原子反变换与逆循环平移,得到去噪后三维地震信号。对含噪的合成与实际地震信号去噪,并与小波、双树复小波、曲波及传统波原子变换的去噪结果对比;结果表明,该算法较其它对比算法有明显优势,且随含噪量的增加,去噪优势愈加明显。从输出信噪比、均方误差以及峰值信噪比等评价指标可知,基于波原子变换的三维地震信号盲去噪算法去噪效果最佳,其次为传统波原子变换算法,然后为曲波变换与双树复小波变换算法,传统小波变换算法的去噪效果最差。     

基于复小波变换与层间模型的图像去噪

很多小波去噪方法认为小波系数是相互独立的,然而大量实验表明实际图像的小波系数之间是有较强的依赖性。在本文中,我们将利用复小波变换的优势以及小波系数之间的依赖性,提出一种新的图像去噪方法。该方法先确定滤波器系数,再对复小波变换系数建模,并根据MAP准则给出系数的收缩方法进行去噪处理,最后作复小波逆变换。同时在变换的系数抽取之前估计系数的方差,可以使方差估计更准确。     

A pose‐invariant approach for hypothesis support

This article presents a tractable and empirically accurate algorithm realizing a midlevel visual process for pattern recognition. The algorithm takes advantage of hypotheses provided by a high‐level visual process, thereby, attempting to extract a region in an image based on these hypotheses. The main focus is to recognize quadrilateral as well as arbitrarily shaped objects from synthetic and real‐world images. The novel approach is based on a study of the Hough Transform and its generalized version. To show overall usefulness of the algorithm, an extensive series of experiments was performed. In particular, occlusion and multiple object‐instances were tested, indicating the effectiveness of this work's approach.© 2003 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 13, 201–207;2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10056     

三维数字循环卷积的二元多项式变换算法研究

对三维数字循环卷积的二元多项式变换算法详细进行了研究和改进,并给出了运算量的估算。我们将看到,改进后的算法对N1×N2×N3的三维复序列的数字循环卷积约需2N1N2N3logN1-8N1N2N3次实乘和4N1N2N3logN1N2N3-N23logN3+2N23次实加,与FFT、FPT方法比较,所需运算量减少。     

Two finite inverse Hilbert transform formulae for region‐of‐interest tomography

Recently we published two explicit formulae for finite inverse Hilbert transforms (You and Zeng, Inv Probl 22 (2006), L7‐L101). This paper presents a straightforward proof of the formulae, the data requirements, and some computer simulations to verify the formulae. Examples of region‐of‐interest tomography using truncated projections and the first formula of the finite inverse Hilbert transform are shown. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 219–223, 2007     

Analysis of effect of cycle spinning on wavelet- and curvelet-based denoising methods on brain CT images

The purpose of this paper is to carry out the assessment of effect of cycle spinning on wavelet- and curvelet-based noise reduction methods on brain CT images. In particular, multiscale curvelet- and wavelet-based denoising methods are evaluated with and without cycle spinning. This assessment is focused not only on the noise suppression but also on fine details preservation. The experimental results show that the cycle spinning-based curvelet method outperforms not only other curvelet-based methods but also the wavelet-based methods. The quality assessment parameters taken in this paper are signal-to-noise ratio (SNR), peak-signal-to-noise ratio (PSNR), universal quality index (UQI), structural similarity index metrics (SSIM), and edge keeping index (EKI).     

3种频域数字水印算法的分析和比较

阐述了离散傅里叶算法(DFT)、离散余弦算法(DCT)、离散小波变换算法(DWT)这3种常用的频域数字水印算法的原理,并分别采用不同算法对数字图像进行了水印嵌入,检测其峰值信噪比(PSNR)和相关系数(NC)的值,分析并比较了这3种算法的优缺点,证明了离散小波变换在频域算法中能够得到最好的效果。     

连续小波变换在函数空间中的应用

某些微分方程和相应的积分方程之间的关系被讨论；这些微分方程通过边境小波变换可被转换成相应的积分方程，它们不仅在弱收敛意义下而且在范围数收敛意义下是等价的；关于这些微分方程的讨论就与相应的积分方程的讨论联系起来。     

Flexible multiple-image encryption algorithm based on log-polar transform and double random phase encoding technique

We present a novel multiple-image encryption algorithm by combining log-polar transform with double random phase encoding in the fractional Fourier domain. In this algorithm, the original images are transformed to annular domains by inverse log-polar transform and then the annular domains are merged into one image. The composite image is encrypted by the classical double random phase encoding method. The proposed multiple-image encryption algorithm takes advantage of the data compression characteristic of log-polar transform to obtain high encryption efficiency and avoids cross-talk in the meantime. Optical implementation of the proposed algorithm is demonstrated and numerical simulation results verify the feasibility and the validity of the proposed algorithm.     

QR code-based non-linear image encryption using Shearlet transform and spiral phase transform

In this paper, we propose a new quick response (QR) code-based non-linear technique for image encryption using Shearlet transform (ST) and spiral phase transform. The input image is first converted into a QR code and then scrambled using the Arnold transform. The scrambled image is then decomposed into five coefficients using the ST and the first Shearlet coefficient, C₁ is interchanged with a security key before performing the inverse ST. The output after inverse ST is then modulated with a random phase mask and further spiral phase transformed to get the final encrypted image. The first coefficient, C₁ is used as a private key for decryption. The sensitivity of the security keys is analysed in terms of correlation coefficient and peak signal-to noise ratio. The robustness of the scheme is also checked against various attacks such as noise, occlusion and special attacks. Numerical simulation results are shown in support of the proposed technique and an optoelectronic set-up for encryption is also proposed.     

图像对比度增强的非线性变换法

对原始图像用所提出的判据判断图像的对比度类型,针对不同类型直接确定灰度变换参数,实现图像全局对比度增强。再对图像进行离散平稳小波变换,利用所提出的非线性增强方法分别对各个分解层的高频子带进行细节增强。实验表明,提出的方法在有效提高图像整体对比度的同时,又能突出图像中目标的细节部分信息。     

粘弹性层状地基轴对称问题的求解

由粘弹性体经Laplace和Hankel变换的基本方程式,得到了轴对称问题情形下无限粘弹性层不同深度应力位移向量间的传递矩阵,利用传递矩阵以及边界、层间完全接触条件求解了多种粘弹性模型的成层地基空间轴对称问题。