Low-up-middle filter,LUM filter for short,is a kind of nonlinear filter developed on the basis of middle filter. An improved LUM filtering algorithm is proposed. The algorithm improves the LUM filter in following two aspects. The algorithm does not filter smoothing areas which are not contaminated by noise,and searches for the position of LU M sharpening window. Comparing with original LUM filter,it can shorten the running time of the program,reduce the noise,keep the useful information and enhance the edge of the image.