Abstract: A method and apparatus for determining the centre photodetector in a planar array of photodetectors of a gamma scintillation camera is provided. The analog signals generated by a plurality of photomultiplier tubes (PMT) following a scintillation event, are digitized, integrated, and stored in a first memory. A first comparison means is used to divide the set of PMT logical signals into groups. Each group comprises an arbitrary number of PMTs. The PMT logical signals within a group are combined into pairs and compared to select the highest intensity value for each individual group. Subsets of local PMT highest intensity values are created. A second comparison means is used to receive the subsets of local PMT highest values, combine them into pairs, compare the paired signals, and record the selected signals in a second memory, until a PMT with the maximum intensity value or a centre PMT is obtained.