a data storage unit of an image compression device for compressing motion picture frame is provided . the data storage unit comprises : a previous frame field having a plurality of slices ; a decoded frame field having a plurality of slices ; and a current frame field having a plurality of slices , wherein the previous frame field stores a previously decoded image and the decoded frame field stores a currently decoded image , wherein the number of slices of the previous frame field is greater than the number of slices of the decoded frame field and the current frame field .