1. A computer-based method for providing image data of a region of a target object, comprising the steps of: estimating a first intermediate object function indicating at least one characteristic of a first sub-region of said region of the target object; estimating a second intermediate object function indicating at least one characteristic of a second sub-region of said region of the target object; and combining the first and second intermediate object functions to form a combined object function indicating at least one characteristic of the region of the target object.