Patent ID: 7876307

Claim:
A method for measuring relative motion between an illuminated portion of a surface and an optical sensing device comprising a coherent light source and a photodetector device, this photodetector device including an array of pixels associated with comparators for comparing light intensity between neighbouring pixels, said method comprising the steps of: illuminating by means of said coherent light source said surface portion at a determined flash rate; detecting by means of said photodetector device a speckled light intensity pattern, defining first and second axes, of said illuminated portion of the surface for each flash and determining in this pattern along said first and second axes positive and negative edges; extracting Peaks and Nulls for each of said detected speckled light intensity patterns by respectively defining successions of a positive edge and a negative edge and successions of a negative edge and a positive edge; determining a measurement of the relative motion between said optical sensing device and said illuminated portion of the surface based on a comparison of extracted Peaks and Nulls of successive detected speckled light intensity patterns; wherein, before the step of determining a measurement of the relative motion, said method further comprises the step of: keeping only pairs of neighbouring Peaks and Nulls and ignoring individually occurring Peaks and Nulls.