An improved image filtering on Rough Sets is proposed in the paper.The method regards the traditional selective masking smooth filtering method as the thinking foundation.According to looking for the mask a pixel belongs to

then the mask RS precision approximation is used to precede image pixel to smooth whole image.It not only realizes cleaning noise and keeping the boundary

but also increases the contrast of picture and makes vision distinction restored picture to original one be minimum.In another words

while denoising the method keeps good details

increases the contrast degree of the picture

and improves the picture quality than the traditional pre-processing method.