A simple algorithm based on noise-detected is presented to remove salt-and-pepper noise from gray-scale image.Each pixel is classified to be signal pixel or possible noise pixel

and the value of possible noise pixels is near 0 or 255.The signal pixels are kept untouched in the filtering process to preserve the detail of the image

while the possible noise pixels are removed by using an improved Adaptive Median Filter

which fixes the noise pixels by utilizing the dot product of the matrix of gray value and a binary matrix

named flag

that is used to record the noise detection results based on improved adaptive Extremum and Median value.A signal pixel is for the value of 1 while a noise is 0 in flag.Simulation results show that the algorithm has strong adaptability to deal with the real noise images.And it can suppress noise effectively and preserve the image details in the high noisy rate.This algorithm outperforms the Standard Median Filtering (SMF) and its improved algorithms for different noise ratio.The PSNR is increased about 6dB on average when the noise rate ranging from 10% to 90%.