External light evasion method for large multi-touch screens

In this paper, we present an external light evasion method that rectifies the problem of misrecognition due to external lighting. The fundamental concept underlying the proposed method is recognition of the differences between two images and elimination of the desynchronized external light by synchronizing the image sensor and inner light source of the optical touch screen. A subtraction operation is used to find differences and the absolute value of the result utilized; hence, order is unimportant. The resultant image, which displays only a touched blob on the touchscreen, is created after image processing for coordination recognition and is then supplied to a coordination extraction algorithm.