1. A method of determining a quality value of a frame, the method comprising the steps of: dividing the frame into a plurality of tiles; determining a motion magnitude for each said tile based upon (i) pixel values of the tile and (ii) pixel values of a corresponding tile of a preceding frame; determining a focus magnitude attribute for each tile of the plurality of tiles having a motion magnitude attribute below a predetermined threshold, the focus magnitude attribute being based on pixel values of the tile; and establishing the quality value of the frame by: (1) testing the motion and focus magnitude attributes of the frame against predetermined criteria; and (2) defining the quality value of the frame depending upon results of said testing.