An apparatus comprising a processor and memory including computer program code, the memory and computer program code configured to, with the processor, enable the apparatus at least to: based on a predetermined dark current component for each photodetector in an array of photodetectors, identify a plurality of subsets of photodetectors from the array for signal readout and amplification by a readout circuit, each photodetector of the array configured to provide a photodetector output signal comprising the dark current component and an image component on exposure to incident electromagnetic radiation from a target scene, wherein each subset of photodetectors is identified such that the combined dark current component of the constituent photodetector output signals for each subset is substantially the same; and provide the identified plurality of subsets for use in signal readout and amplification by the readout circuit.