According to a first aspect of the invention there is provided a system of and method for processing a digitized image derived from detector instrumentation (11) to form a reconstructed image. In a typical image processing system (9), γ-rays (10) impinge upon a gamma camera unit (11), defining detector instrumentation, and then pass through a lead collimator (12) to cause a scintillator (14) to emit light in the visible electromagnetic spectrum at given locations above an array of analogue photomultiplier tubes (16). With appropriate circuitry (18) these analogue signals may then be digitized, by means of processor (20), and then stored in memory (22). The present invention aims to more accurately reconstruct these digital images, with, in broad terms, the raw data stored in memory (22) being sent to a processor (24), which processes the data in terms of algorithms that form part of the invention. According to a further aspect of the invention there is provided a method of processing a digitized phantom image derived from detector instrumentation to form a reconstructed point spread function image.