It is described a method for measuring the movement of an optical pointing device on a work surface, which includes a pixel photo-detector array to pick-up reflected light on the work surface, a window comparator array receiving pixel voltages and providing comparison signals to a processing circuit. Light intensity between neighboring pixels is compared to determine edge direction data, which includes a positive edge for a first pixel voltage smaller than a second pixel voltage by more than a half of a window voltage, a no-edge, with the difference between the pixel voltages smaller than the half of the window voltage, and a negative edge, for which the first pixel voltage is greater than the second pixel voltage by more than the half of the window voltage. Two edge direction data from two successive flash are compared to determine the relative motion of the pointing device on the work surface.