US Patent 7907120 Optical mouse with uniform level detection method

Movement of an optical mouse may be tracked by providing a source of non-coherent light in a movable housing for illuminating a work surface at a low angle of incidence, providing a two dimensional array of photo detectors for producing arrays of data elements responsive to light reflected from surface irregularities on the illuminated work surface and providing circuitry for capturing a first array of data elements from the two dimensional array of photo detectors at a first time, for detecting a characteristic condition in the first array, for capturing a second array of data elements at a second time, and for tracking movement of the housing relative to the work surface by comparing at least some of the data elements of the first array with at least some of the data elements of the second array if the characteristic condition is not detected in the first array. Movement may be tracked by providing a source of non-coherent light in a movable housing for illuminating a work surface at a low angle of incidence, providing a two dimensional array of photo detectors for producing arrays of data elements responsive to light reflected from surface irregularities on the illuminated work surface and providing circuitry for tracking movement of the housing relative to the work surface by comparing light reflected from the surface irregularities at a first time with light reflected there from at a second time unless the light reflected at the first time does not include a characteristic condition.