Abstract: To remove the impulse noise from the image，on the basis of research for the previous switching median filters，an improved median filtering algorithm based on two-stage noise detection is proposed.This algorithm analyzes and overcomes the shortcoming of the local extremum misjudgement of the max-min noise detector by adding the second noise detection with the local energy of image pixel.The noise pixels are removed using the improved median filtering，while signal pixels hold their gray value and are unprocessed.Simulation results show that this algorithm has the ability of removing noises and the ability of preserving the partial details of images in comparison with some recent methods especially when the noise density is very high.

Key words: impulse noise, switching median filter, noise detection, local energy

摘要： 针对脉冲噪声感染的图像，借鉴开关滤波的思想，提出了一种新的改进算法。该算法通过分析Max-min噪声检测算子的图像灰度局部极值点的误判缺陷，在极值检测的基础上，增加了由局部能量信息为判别依据的第二级噪声检测过程，实现了对噪声的精确检测。同时，在去除噪声时只利用信号点参与中值滤波，并让噪声点逐步转化为信号点，减少了噪声在邻域的传播。实验表明，该算法对脉冲噪声具有很好的噪声滤除和细节保护能力，与传统中值滤波及其他开关滤波算法相比，该算法具有更优的滤波性能，即使是在噪声密度较高的情况下，也能取得令人满意的效果。

关键词: 脉冲噪声, 开关中值滤波, 噪声检测, 局部能量