US Patent 7359090 Shading an optical sensing element such as in a scanner

Method for shading one of a first plurality of sensing elements of an optical sensor. High-reflectivity and low-reflectivity reference values of the output signal of each of a second plurality of sensing elements of the sensor are obtained. An average or nominal high-reflectivity value of the high-reflectivity reference values for each sensing element of the second plurality is calculated. An average or nominal low-reflectivity value of the low-reflectivity reference values for each sensing element of the second plurality is calculated. An offset value for one of the sensing elements of the first plurality is calculated using at least the average or nominal high-reflectivity values and the average or nominal low-reflectivity values. The one sensing element of the first plurality is calibrated using at least the calculated offset value. In one example, the first plurality and the second plurality are identical.