Patent ID: 7864982

Claim:
A displacement detection method for a portable autonomous device having an integrated image sensor, said method comprising: a) receiving a current digital image from said image sensor, said current digital image depicting a background scene; b) choosing the position of a first area within said current digital image; c) receiving a later digital image from said image sensor depicting an overlapping portion of said background scene; d) identifying the position of a second area matching said first area within said later digital image, said matching being such that said first and second areas depict the same portion of said background scene; and e) calculating a said current motion vector of said portable autonomous device according to a displacement between said first area and said second area, wherein said identifying of step (d) is performed according to the following steps: i) separately evaluating a distortion measure of each one of a plurality of area candidates according to differences in representational information from said first area; ii) evaluating a quality level of said motion vector, said quality level determined according to said distortion measures; and iii) choosing one of said area candidates as a matching area, said chosen matching area candidate having the lowest distortion measure; and further comprising a step of storing said motion vector as a previous motion vector, wherein said calculating of step (e) is performed according to the following steps: i) if said current quality level does not exceed a predefined threshold, substituting said previous motion vector as the outcome; and ii) if said current quality level does exceed said predefined threshold, calculating said current motion vector.