Pixel circuits in an image sensor are sampled repetitively during an image frame period. At each sampling, a signal indicative of the photocharge integrated by a pixel circuit since last reset is compared to a threshold. If the integrated photocharge signal has not reached the threshold, the pixel circuit is permitted to continue integrating photocharge. If the integrated photocharge signal has reached the threshold, the pixel circuit is reset to remove integrated photocharge and photocharge integration for that pixel circuit is restarted. A corresponding pixel circuit value is recorded for the reset pixel circuit.