US Patent 11301089 Stylus identification

An optical IR touch sensing apparatus configured to determine, based on output signals of light detectors, a light energy value for each light path across a touch surface, and generate a transmission value for each light path based on the light energy value. A processor is then configured to operate an image reconstruction algorithm on at least part of the thus-generated transmission values and determine a position of a touching object on the touch surface, and an attenuation value corresponding to the attenuation of the light resulting from the object touching the touch surface. Using these values, the processor is configured to identify the type of object.