US Patent 7405727 Lift detection mechanism for optical mouse sensor

A method for detecting a lift condition from an illuminated surface portion of an optical motion sensing device. According to a first embodiment, two different “loss-of-focus” thresholds are used. A first threshold is used when the optical pointing device is not moving, and a second threshold greater than the first one is used when the optical pointing device is moving. The optical device further requires means for detecting whether it is moving or not. According to a second embodiment, a dynamical loss-of-focus threshold depending on an average number of motion features that the surface exhibits to the sensor of the optical pointing device is used.