A block prediction search method includes at least following steps: utilizing a data buffer to store bit-depth reduced sample values of a plurality of samples in a first pixel line; detecting occurrence of an edge in the first pixel line according to restored sample values derived from stored sample values in the data buffer; and determining a block prediction vector for a pixel group in a second pixel line different from the first pixel line, wherein the block prediction vector is determined based at least partly on a last edge count value indicative of a number of samples in the first pixel line that have gone by since the edge occurs.