1. A motion estimation method, applied to a video signal comprising a first frame and a second frame, the method comprising: capturing a matching window from the first frame; capturing a searching area from the second frame, the searching area comprising a plurality of searching blocks each having a size equal to that of the matching window; selecting a searching block from the plurality of searching blocks; calculating a difference between pixel data of the selected searching block and pixel data of the matching window to simultaneously obtain N total differences corresponding to N different searching blocks, N being an integer greater than 1; and determining a motion vector corresponding to the matching window according to at least the N total differences, wherein the steps of selecting a searching block from the plurality of searching blocks and calculating the difference between pixel data of the selected searching block and the pixel data of the matching window comprises: selecting a matching window sampling area from the matching window; defining N searching block sampling areas within the selected searching block, each of the N searching block sampling areas having a size equal to that of the matching window sampling area; and respectively calculating a difference between each of the searching block sampling areas and the matching window sampling area to obtain the N total differences corresponding to the N searching blocks.