Method and sensing device for motion detection in an optical pointing device, such as an optical mouse

Abstract

There is described a method for measuring relative motion between an illuminated portion of a surface and an optical sensing device comprising a photodetector array including a plurality of rows and columns of pixels respectively aligned along first and second axes comprising essentially the steps of comparing at a first point in time light intensity between neighbouring pixels of the photodetector array and determining along each of the first and second axes, edge direction data from the detected first light intensity pattern, extracting edge inflection data from the edge direction data from the detected first light intensity pattern, comparing at a second point in time light intensity between neighbouring pixels and determining along each of said first and second axes, the edge direction data from the detected second light intensity pattern, extracting edge inflection data from the edge direction data from the detected second light intensity pattern. The method further comprises the steps of extracting inflection line data being descriptive of the succession of two adjacent edge inflection data of the same type transversal to at least one determined axis, counting a total number of the extracted line conditions and determining a measurement of the relative motion between the optical sensing device and the illuminated portion of the surface along the determined axis based on a ratio of a comparison of the edge inflection data previously extracted and a function of the total number of inflection conditions and the total number of line conditions.