一种有效去除椒盐噪声的开关中值滤波器

An Efficient Switching Median Filter for the Removal of Salt and Pepper Noise

图像去噪追求的目的是既能去除图像中的噪声,同时又能较完整的保持图像的细节信息。在研究几种基于中值的椒盐噪声去除方法基础上,设计了一种有效去除图像椒盐噪声的开关中值滤波器。提出的算法首先利用图像灰度值的两个极值把像素点分为信号点和可能噪声点。在滤波阶段,对于信号点保持其灰度值不变,对于可能噪声点分两步进行处理:根据噪声密度决定滤波窗口尺寸并判断滤波窗口内是否包含信号点,如果无信号点则以窗口内像素的中值作为可能噪声点的恢复值,这一步可对误判噪声点进行纠正;而其余可能噪声点采用极值舍弃滤波和递归滤波估计其灰度值,滤波窗口尺寸固定为3×3,这一步用来去除噪声和保持图像细节。实验结果表明,本文算法在主客观方面都优于相比较的方法,且对不同水平的椒盐噪声都具有较好的去除性能。

After analyzing several median - based methods for the removal of salt - and - pepper noise, an effi- cient switching median filter for the removal of salt and pepper noise is presented. The proposed filter first di- vides pixels into two categories： noise -free and possible ＂noise pixels＂ based on two extreme intensity values in an image. In the filtering stage, when a pixel is classified as noise - free it will be left unchanged. For a ＂noise pixel＂, it is subjected to the following two - step filtering scheme. In the first step, if the filtering window, ob- tained according to noise density, contains no noise - free pixel, then the median of the filtering window is used as the restored value of the current pixel. Such filtering can restore misadjusted pixels as many as possible. Oth- erwise, extremum - rejection filtering and recursive filtering are applied to the rest of ＂noise pixels＂ by using the fixed 3 - 3 filtering window, which is used for noise removal and preserving image details. Experimental results show the proposed filter outperforms those of the compared filters in terms of both quantitative evaluation and vis- ual quality, meanwhile exhibiting good performance for different noise levels.