A motion estimation method for a succession of frames in a digital coding system includes: a) with reference to a first block in a first frame, searching a second frame for a second block that corresponds to the first block; and b) estimating a motion vector of the first block on the basis of the second block in the second frame; wherein step a) includes: a1) forming a first initial search range including a virtual rhombus-shaped pattern substantially centered at a pre-determined block, and a2) expanding progressively outward a second initial search range based on the virtual rhombus-shaped pattern.