A technique for optical navigation involves summing intensity values from a photodetector array on a per-column and a per-row basis for both reference image data and sample image data and then performing separate one-dimensional cross-correlations on the per-column sums and on the per-row sums to separately...http://www.google.co.uk/patents/US7315013?utm_source=gb-gplus-sharePatent US7315013 - Optical navigation using one-dimensional correlation
