1. A method of generating a detector position map for an array of detectors, the detector position map comprising a map which maps measured coordinates from a detection event to the detector in the array which detected the detection event, the method comprising the steps of: illuminating an array of detectors with a source of radiation to generate a histogram, the histogram comprising an event count as a function of two dimensions, the two dimensions corresponding to a face of the array of detectors, wherein the histogram comprises a plurality of first peaks; modifying the histogram to comprise a plurality of second peaks, wherein the second peaks have a greater degree of isolation from each other than the first peaks; and for each detector, determining a region on the detector position map which corresponds to the detector, each region being based on a position of one of the second peaks.