Patent ID: 8432377

Claim:
A touch detection system, comprising: a light detection system having an optical center and configured to detect patterns of light received from a touch area; a retroreflector positioned along at least one edge of a touch surface in the touch area; a primary illumination system configured to emit light across the touch surface towards the retroreflector so that at least some of the light ultimately originating from the primary illumination system is retroreflected to the light detection system in the absence of an object in the touch area; a secondary illumination system configured to emit light across the touch surface so that, in the presence of the object in the touch area at least some of the light ultimately originating from the secondary illumination system is reflected by the object to the light detection system; and at least one computing device interfaced with the light detection system and configured to determine a position at which the object present in the touch area has interfered with light traveling across the touch surface by: generating an error signal based on a secondary detected pattern of the light ultimately originating from the secondary illumination system, wherein the error signal is indicative of the object being sufficiently close to the light detection system to cause a variance in a primary detected pattern of the light ultimately originating from the primary illumination system, and subtracting the intensity of the error signal from the intensity of the primary detected pattern.