1. A method for determining true motion vectors between a current and a previous frames for feature points, each of the feature points being defined in terms of a position of a pixel located at a node of a rectangular grid mapped on the previous frame, the method comprising the steps of: (a) assigning each of the feature points as a subject feature point in sequence, wherein the subject feature point is surrounded by its neighboring four feature points, to thereby define a previous rhombus, the previous rhombus having a set of four triangle regions, each of the triangles being formed by connecting the subject feature point and its two neighboring feature points; (b) detecting a first set of initial motion vectors for the feature points between the current frame and the previous frame; (c) providing a predetermined N number of displacements to each of the initial motion vectors for its corresponding subject feature point to thereby produce a subset of N candidate motion vectors; (d) defining a current rhombus in the current frame corresponding to each previous rhombus through the use of the first set of initial motion vectors; (e) generating N sets of four triangles in each current rhombus based on the N candidate motion vectors; (f) deriving a predicted pixel from the previous frame for each pixel contained in each set of four triangles within each current rhombus to provide a predicted pixel value therefor; (g) producing a differential pixel value for said each pixel contained in each set of four triangles by subtracting the predicted pixel value from the pixel value of said each pixel; (h) calculating N error values for said N sets of triangles in each current rhombus by averaging the differential pixel values corresponding thereto; (i) comparing said N error values to select an error value which entails a minimum error; and (j) choosing a motion vector, which corresponds to the selected minimum error value, from each subset of N candidate motion vectors as a true motion vector.