Abstract: In a charge transfer device imager, photodetector output current is accumulated and stored during an integration period in an analog potential well in the substrate surface potential adjacent the photodetector, the analog well being reset each time the detector changes the amount of stored charge by a preselected fraction of the storing well capacity, simultaneously incrementing a digital count. At the end of each integration period, both the contents of the analog well and the digital count are read into an output register. As a result, the length of the integration period may be significantly extended without regard to the charge storing capacity of the charge transfer device, thus improving the signal-to-noise ratio and the dynamic range of the imager. In the preferred embodiment, the amount of charge stored in the analog potential well is sensed by sensing the potential of the photodetector, where the photodetector comprises a diode diffusion in the substrate.