A method for comparing a target block to a reference window in motion estimation calculations, comprises the steps of: determining SAD calculations as a function of the target block and the reference window; reading the target block into registers; reading a segment of the reference window; updating the determined SAD calculations on the fly as a function of the read target block and the read segment of the reference window; and determining one or more sub-blocks of the reference window having minimum SAD values as a function of the updated SAD calculations; and if one or more of the minimum SAD values are not found, repeating the reading a segment step, the updating step and the determining step for a next segment of the reference window.