An image sensor has an array of pixels, each pixel having an associated shutter transistor coupled to transfer a charge dependent on light exposure of the pixel onto an image storage capacitor, the image-storage capacitors being configured to be read into an analog to digital converter. The shutter transistors are P-type transistors in N-wells, the wells held at an analog power voltage to reduce sensitivity of pixels to dark current; in an alternative embodiment the shutter transistors are N-type transistors in P-wells, the wells held at an analog ground voltage.