In this work we compare different calibration sources and focus on their combination to optimize the calibration of large-format X-ray imagers over a wide range. This activity is carried out in the framework of the DSSC project and the primary aim is the calibration of the DSSC camera. We considered pulsed IR laser, radioactive sources, X-ray tube, electrical injection devices, X-ray synchrotron beam, low-energy protons, LED sources. The relevant features (deposited energy and pulse width) are critically summarized and calibration strategies will be discussed.