Systems and methods for correcting output signals from non-linear photosensors, specifically silicon photomultipliers (SiPMs). SiPMs are used in a PET detector to readout light emissions from LSO scintillator crystals. The non-linear output of the SiPM can distort and compress the energy spectrum which is crucial in PET imaging. The non-linearity effect for inter-crystal scattered events can place an energy event outside of the PET detector energy window, resulting in a rejected event. Systems and methods to correct the SiPM non-linearity for inter-crystal scattered events, so as to be able to obtain the proper energy event and produce an accurate medical image, are disclosed.