A filter for a video stream is provided. The filter generates a filtered picture according to a current picture and its previous picture. A motion difference calculator accumulates differences between current picture values and previous picture values within a neighborhood of each pixel to provide a corresponding motion difference. A histogram counter performs histogram counting according to motion differences of the pixels. A filter value calculator provides a filter value for each pixel according to operations of the motion difference calculator and the histogram counter. A blender blends the current picture value and the previous picture value of each pixel according to weightings correlated to the filter value, and provides a filtered picture value for each pixel of the filtered picture.