1. A electronic device, comprising: a touch-sensitive display screen including an array of electromagnetic radiation emitters and electromagnetic radiation detectors, wherein the array of electromagnetic radiation detectors is configured to generate an image signal that represents an image of a user input object that is closely spaced to the display responsive to detected electromagnetic radiation that is reflected by the user input object; and a controller circuit configured to control activation of the array of electromagnetic radiation emitters so that at least a portion of the array of electromagnetic radiation emitters are inactive in an absence of detecting electromagnetic radiation reflected by the user input object, and to selectively activate ones of the array of electromagnetic radiation emitters responsive to the array of electromagnetic radiation detectors detecting electromagnetic radiation that is reflected by the user input object, wherein the controller circuit is configured to activate a first set of one or more of the electromagnetic radiation emitters and to generate a first electromagnetic radiation profile responsive to electromagnetic radiation from the first set of one or more electromagnetic radiation emitters that is reflected by the user input object and detected by the array of electromagnetic radiation detectors, the controller circuit is configured to activate a second set of one or more of the electromagnetic radiation emitters that is different from the first set of one or more of the electromagnetic radiation emitters and to generate a second electromagnetic radiation profile responsive to electromagnetic radiation from the second set of one or more electromagnetic radiation emitters that is reflected by the user input object and detected by the array of electromagnetic radiation detectors, and the controller circuit is configured to identify a contour profile of the user input object based on the first and second electromagnetic radiation profiles.