The present application discloses methods and systems for calibrating a scanning system. In one embodiment, the calibration method determines a dark level of at least one pixel, determines a maximum white level for at least one pixel and adjusts the current of an illumination source based upon an output of an analog to digital converter. In another embodiment, the scanning system has a circuit for dynamically adjusting the output of an illumination source. The circuit has a pulse width modulated signal generator for generating a pulse width modulated signal and a driver for receiving the pulse width modulated signal and causing current to the illumination source to be modulated based on the pulse width modulated signal.