1. A motion estimation method for blocks of a periodic pattern, comprising: determining a global motion vector corresponding to a region in a first frame according to motion vectors of periodic blocks in the region in the first frame, wherein the region is one of a plurality of regions divided from the first frame and the periodic blocks in the region are a part of the periodic pattern; generating a plurality of candidate motion vectors of a target periodic block to be encoded in a second frame; for each candidate motion vector, determining a penalty value based on at least one difference between the candidate motion vector and at least one global motion vector corresponding to at least a relative region in the first frame, wherein the at least one relative region is associated with the target periodic block; for each candidate motion vector, calculating a weighted similarity value based on an original similarity value between the target periodic block of the second frame and a reference block corresponding to the candidate motion vector of the first frame, and the penalty value; and determining a motion vector of the target periodic block according to weighted similarity values of the candidate motion vectors.