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.