An image sensor, for example for incorporation within an active matrix display, comprises an array of sensor elements 10. Each sensor element (10) comprise an amplifying transistor (M1) whose gate is connected to an integrating node (11). The integrating node (11) is connected to one plate of an integrating capacitor (C1) and to one electrode of a photodiode (D1), whose other electrode is connected to a resetting line (RST). The sensor element (10) performs a repeating sensing cycle comprising a resetting phase, an integrating phase and a reading phase. During the resetting phase, the resetting line (RST) receives a voltage which forward-biases the photodiode (D1) so as to charge the integrating node (11) to a predetermined voltage. The resetting line (RST) is then returned to a voltage for reverse-biasing the photodiode (D1) so that the integrating and reading phases may be performed.