G06F 3/0426

Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by opto-electronic means {using a single imaging device like a video camera for tracking the absolute position of a single or a plurality of objects with respect to an imaged reference surface, e.g. video camera imaging a display or a projection screen, a table or a wall surface, on which a computer generated image is displayed or projected tracking fingers with respect to a virtual keyboard projected or printed on the surface }