A method of determining a movement vector between two images is disclosed. The two images are sequentially taken by an optical mouse. The method comprises first calculating a directional correlation value for a plurality of directional shifts between the first image and the second image. The minimum directional correlation value is chosen and compared to a threshold value. If the minimum directional correlation value calculated is less than the threshold, identifying a movement vector associated with the minimum directional correlation value. However, if the minimum directional correlation value is not less than the threshold, the first and second images are compressed and the calculations are redone. The compression continues until a qualifying movement vector is identified.