关键词: 非线性, 图形恢复, 中值滤波, 噪声, 自适应

Abstract: For keeping the details of an image when removing noise，a novel adaptive filter is proposed.According to whether the gray value of a pixel is its neighborhood extremum，all pixels are divided into two types，doubtful noise and signals.If the center pixel is doubtful noise，the signals，together with the center pixel，are recognized as a new type.By comparing the difference between the median of the signals and the new type with the threshold，it can be decided that if the original gray value should be instead by the median of the signals.The size of the window can change adaptively along with the density of the noise.In simulation experiment，it is proved that the filter has an excellent performance and is more effective than ordinary median filter especially on high noisy rate situations.

Key words: non-linear, image restoration, median filter, noise, adaptive