Pen differentiation for touch display

A method of determining a type of object in contact with a touch surface of a touch sensing apparatus, said touch sensing apparatus comprising:

• a touch surface,
• a plurality of emitters, arranged around the periphery of the touch surface, configured to emit beams of light such that one or more objects touching the touch surface cause an attenuation of the light;
• a plurality of detectors, arranged around the periphery of the touch surface, configured to receive light from the plurality of emitters on a plurality of light paths, wherein each detector in the plurality of detectors is arranged to receive light from more than one emitter in the plurality of emitters;
• and
• said method comprising the steps of:
• determining, based on output signals generated by the plurality of detectors, a light energy value for each light path of the plurality of light paths;
• generating a transmission value for each light path of the plurality of light paths based on the light energy value;
• from at least part of the thus-generated transmission values, determine for each object;
• a position of the object on the touch surface, and
• an attenuation value corresponding to the attenuation of the light resulting from the object touching the touch surface,
• an occlusion compensation value indicative of the occlusion, by other objects on the touch surface, of light paths intersecting with the object;
• determining an object type of the object in dependence on the attenuation value and occlusion compensation value.