A digital unit cell, readout circuit for a digital unit cell and a method of operating an analog counter of a digital unit cell is disclosed. The readout circuit includes storage capacitor for storing a voltage remaining at an analog counter at the end of an integration period, and a comparator circuit. The comparator circuit compares a dummy voltage provided from the analog counter during a readout period to the voltage at the storage capacitor, and determines the voltage at the storage capacitor when the dummy voltage falls below the voltage at the storage capacitor.