Image sensors and methods of using image sensors are disclosed. In an embodiment, the image sensor includes pixel regions having optically sensitive material (OSM). A bias voltage is provided to the OSM via a bias electrode for each pixel region. A pixel circuit (PC) for each pixel region includes a read out circuit and a charge store (CS) coupled to the OSM of the respective pixel region. The PC resets voltage on the CS to a reset voltage during a reset period, integrates charge from the OSM to the CS during an integration period, and reads out a signal from the CS during a read out period. The PC includes a reference voltage node coupled to the CS during the reset period and the read out circuit during the read out period, a reference voltage is applied to the reference voltage node and is varied during operation of the PC.