Patent ID: 8427648

Claim:
An apparatus that discriminates between a first surface type and a second surface type wherein said first surface type's reflectivity is higher than said second surface type's reflectivity comprising: a light source that illuminates said first surface type or said second surface type; a photosensor that measures the reflectivity of said first or second surface type; a first gain element that adjusts a voltage or current from said photosensor based on said measured reflectivity; a second gain element that adjusts a measurement of a current or a voltage supplied to said light source; a subtractor that subtracts the first adjusted voltage or current from the first gain element and the adjusted measurement from the second gain element to provide a subtractor output value; wherein said subtractor output value is zero with respect to said second surface type and said subtractor output value is at a maximum with respect to said first surface type; a threshold value generator that generates a threshold reference value; and a comparator which compares said subtractor output value and said threshold reference value and indicates whether said first surface type or said second surface type is present.