Abstract: A read-out circuit for a photodetector incorporates a photodiode detector (1) connected via a preamplifier (2) to a storage capacitor (C.sub.5). The capacitor (C.sub.5) is also connected to a constant current circuit (C.sub.c, T.sub.3 to T.sub.7) providing a correction current controlled by a voltage on a reference capacitor (C.sub.c). The reference capacitor (C.sub.c) is charged by the amplified photodiode output current during a calibration phase. During a measurement phase, the storage capacitor (C.sub.5) integrates the difference between the amplified photodiode output current and the correction current. This provides pedestal signal substraction at the signal integration point. An array of photodetectors may be provided with a corresponding array of read-out circuits integrated in a single semiconductor substrate.