一种图像增强新方法

提出了一种四树复小波包变换域层内层间系数相关性图像增强新方法。该方法利用四树复小波包变换具有移不变性、良好方向选择性和对高频信号的细致分析能力,把含噪图像分解成低频逼近子图和若干高频方向子图;在保留低频逼近子图复系数不变的同时,充分利用变换域信号复系数层间相关性强和噪声复系数层间相关性弱的特点,采用非高斯双变量模型对每一个方向子图复系数进行降噪处理。同时考虑图像的弱边缘在变换域某些方向子图内复系数值较大,而在其他方向子带内其值较小的特点,甄别出弱边缘点对应的复系数并进行增强处理。实验结果表明,无论是PSNR指标,还是在视觉效果上,该方法的增强性能均好于传统的双树复小波变换去噪、四树复小波包变换去噪和小波域高斯尺度混合模型去噪,在有效抑制噪声的同时,具有很好的图像弱边缘增强和细节保护能力。

Image denoising using statistical model based on quaternion wavelet domain

Image denoising is the basic problem of image processing. Quaternion wavelet transform is a new kind of multiresolution analysis tools. Image via quaternion wavelet transform, wavelet coefficients both in intrascale and in interscale have certain correla- tions. First, according to the correlation of quaternion wavelet coefficients in interscale, non-Ganssian distribution model is used to model its correlations, and the coefficients are divided into important and unimportance coefficients. Then we use the non-Gaussian distribution model to model the important coefficients and its adjacent coefficients, and utilize the MAP method estimate original image wavelet coefficients from noisy coefficients, so as to achieve the purpose of denoising. Experimental results show that our al- gorithm outperforms the other classical algorithms in peak signal-to-noise ratio and visual quality.

硬化非高斯模型及其在首次穿越中的应用

提出了一个硬化非高斯过程的首次穿越概率计算方法.对比研究了Winterstein硬化模型、正交展开模型以及四阶矩标准化函数在硬化反应阶段的适用范围与精度.结果表明：四阶矩标准化函数精度最高,适用于峰度系数不小于2.333的应用场合;正交展开模型精度高于Winterstein硬化模型,适用范围分别为峰度系数不小于1.25和1.0的应用场合.基于硬化非高斯过程的峰度系数取值,以四阶矩标准化函数、正交展开模型以及Winterstein硬化模型为体系建立了首次穿越概率计算方法.最后,以硬化非高斯风压为例,验证了本文方法在首次穿越中的应用的可行性.