Handheld electronic devices provide functionalities which continue to be enhanced. With increasing processing capabilities and functionalities provided in the handheld electronic device, it is increasingly challenging to provide input interfaces which allow the variety of functionalities to be controlled in an intuitive manner. Touch sensors which sense a touch action enhance the ways in which a user may interact with the handheld electronic device. Touch sensors may be configured such that they provide information on the location at which a user touches a window. Touch sensors may be configured to discriminate multi-touch scenarios in which several fingers are used to simultaneously actuate different regions of the touch sensor panel, and/or to track the movement of a user's finger across the window. Such detection capabilities allow different functionalities of the handheld electronic device to be controlled in a way in which the location of one or plural touch actions or a movement pattern of the user's fingers across a window may encode different control commands. The two-dimensional position(s) of the touch action are the input data which are evaluated to control operation of the handheld electronic device.
One approach to further enhance the operation of the input interface is to derive information on a size of an area at which a user contacts the window of the input interface. The size of this area provides information on the way in which the user places his or her finger against the window. For illustration, the area over which a touch sensor is actuated may vary depending on whether the user pushes more or less strongly against the window, or depending on whether a smaller or larger finger is placed against the window. While this approach does not require a separate sensor and derives additional information from the size of the area in which the user's finger contacts the input interface, it has shortcomings. It may be challenging or impossible to discriminate cases in which a user pushes against the window lightly with his index finger from cases in which the user pushes strongly with his little finger. When a user places a rigid object, such as a pen-type device, against the window, it is inherently difficult to derive information other than the two spatial coordinates defining the position of the touch action with conventional touch sensors.