Patent ID: 8482547

Claim:
A method in a touch-sensing apparatus, said apparatus comprising a light transmissive panel that defines a touch surface and an opposite surface, a light source arrangement for providing sheets of light inside the panel, wherein each sheet comprises light that propagates by internal reflection between the touch surface and the opposite surface-from one or more incoupling points to a set of outcoupling points, said apparatus further comprising a light sensor arrangement for generating one or more output signals that represent light reaching the outcoupling points, wherein the touch-sensing apparatus is configured such that an object touching the touch surface locally attenuates at least two sheets of light, said method comprising: identifying, in said output signal(s), a set of signal profiles originating from said object, determining at least part of an attenuated light path across the panel based on each signal profile, and identifying the position of the object on the touch surface based on the thus-determined attenuated light paths, wherein said determining comprises applying a width function which is representative of a dependence of signal profile width on distance to the incoupling point due to light scattering caused by a diffusing structure of at least one of the touch surface and the opposite surface, wherein at least one of the sheets is generated in the form of a diverging beam originating at the one or more incoupling points, and wherein said determining includes, for each signal profile associated with said at least one sheet generated in the form of a diverging beam, identifying outcoupling points corresponding to limits of the signal profile, reconstructing limiting rays of the attenuated light path by geometrically retracing the thus-identified outcoupling points to a respective incoupling point, and modifying the distance between the limiting rays by applying said width function, thereby determining the attenuated light path.