基于Contourlet变换的红外图像非线性增强算法  

Infrared Image Nonlinear Enhancement Algorithm Based on Contourlet Transform

作　　者：石丹[1] 李庆武[1] 倪雪[1] 霍冠英[1] 

机构地区：[1]河海大学计算机及信息工程学院,江苏常州213022

出　　处：《光学学报》2009年第2期342-346,共5页Acta Optica Sinica

基　　金：国家863计划(2007AA11Z227);江苏省社会发展科技项目(BS2007058);常州国家高新区科技攻关项目(XE120070614)资助课题

摘　　要：针对红外图像对比度低、噪声大等特点,提出一种基于Contourlet变换的红外图像非线性增强算法。Contourlet变换是一种有效的方向多尺度变换分析方法,能在任意尺度上实现任意方向的分解。首先采用Contourlet变换对图像进行多尺度、多方向分解,得到低频子带系数和各带通方向子带系数。引入非完全贝塔函数对低频子带系数进行处理,提升图像整体对比度;采用非线性增益函数对各带通方向子带系数进行处理,通过估计噪声水平设定阈值,抑制绝对值小于阈值的系数,增强大于阈值的系数。最后经Contourlet逆变换得到增强图像。实际实验结果表明,该方法可以有效地增强低对比度红外图像,无论是在视觉效果上还是在图像对比度评估值定量指标上均明显优于直方图均衡化、小波变换增强等方法,且能保持更多的图像轮廓特征,克服了这些方法对噪声增强过度和图像细节增强不足等缺点。Considering the low contrast and strong noise of infrared images, an infrared image nonlinear enhancement algorithm based on Contourlet transform is proposed. As an efficient directional multiresolution image representation method, Contourlet transform can offer different number of directions at different scales. Firstly, Contourlet transform is performed on the original infrared image at different scales and directions, thus the low frequency subband coefficients and varieties of directional bandpass subband coefficients are obtained. Then, incomplete beta function is applied to enhance the image＇s global contrast in the low frequency subband, and nonlinear gain function is used to process the coefficients at each scale in the directional bandpass subbands respectively, which suppresses small coefficients and enhances big coefficients by threshold denoising method. Finally, the enhanced infrared image is obtained by transforming these changed coefficients back to the spatial domain. The experimental results show that the algorithm proposed in this paper has advantages of enhancing low contrast infrared image efficiently over other methods, such as histogram equalization and wavelet transform enhancement. Our method can preserve more characteristics and reduce the noise of original image. It is superior to general histogram equalization and wavelet transform enhancement whatever in visual effect or in quantitative contrast parameter.

关 键 词：图像处理 图像增强 CONTOURLET变换 红外图像 非完全贝塔函数 非线性增益函数 

分 类 号：TN911.73[电子电信—通信与信息系统]