An image sensor circuit, comprises: a photo sensing circuit including a photo sensitive device for sensing a light signal to generate a photo sensing signal at a photo sensing output node; a charge storage device, coupled to an integration node; an integration switch coupled between the photo sensing output node and the integration node, operating according to an integration control signal; and a reset circuit coupled between a voltage supply and the integration node, operating according to a reset control signal and a read control signal, wherein the integration node includes an integration voltage. In a reset time period, the integration switch is conductive, and the reset circuit generates a reset signal on the integration node to bias the photo sensitive device through the integration switch to an active state and to charge the charge storage device such that the integration voltage is determined to be at a reset level.