A motion estimation method for a frame rate converter includes generating a plurality of unidirectional motion vectors (MVs) based on a first original frame and a second original frame; classifying each of the plurality of unidirectional MVs as a reliable MV or a mismatch MV; mapping the reliable MV onto one of a plurality of blocks of an interpolation frame; classifying each of the plurality of blocks as a high confidence block or a low confidence block based on whether there is at least one reliable MV mapped onto the block; and determining an assigned MV for each of the high confidence block by selecting one of the at least one reliable MV mapped onto the high confidence block.