Tracking objects on a touch surface

A device for tracking movement of one or more objects on a touch surface of a touch-sensitive apparatus, the touch-sensitive apparatus being operable to propagate light by internal reflections inside a light transmissive panel from a plurality of incoupling points to a plurality of outcoupling points so as to illuminate the touch surface from within the light transmissive panel, wherein a light sensing means is optically coupled to the outcoupling points to generate an output signal representing received light at the outcoupling points, said device comprising:

• means for processing the output signal to generate an interaction map that indicates local changes in interaction on the touch surface;
• means for processing the interaction map for identification of positive and negative apparent peaks, wherein each positive apparent peak represents a locally increased interaction in the interaction map and each negative apparent peak represents a locally decreased interaction in the interaction map;
• means for processing the positive and negative apparent peaks to identify potentially false peaks among the positive and negative apparent peaks;
• and means for updating, based on the potentially false peaks, movement trajectories of all objects deemed to exist on the touch surface at a preceding time point,
• wherein the means for processing the positive and negative apparent peaks is configured to apply at least one of a first heuristic and a second heuristic for identifying the potentially false peaks, said first heuristic designating a positive apparent peak as a potentially false peak when the positive apparent peak is deemed to be associated with one or more of the negative apparent peaks, and said second heuristic designating a positive apparent peak as a potentially false peak when the positive apparent peak is deemed to be located along one of the movement trajectories.