An image processing device of a computer tomography system includes an interface and a calibration data determiner. The interface is implemented to receive a first set of X-ray recordings of an object to be examined from first discrete recording angles and to receive a second set of X-ray recordings of the object to be examined from second discrete recording angles. The calibration data determiner is implemented to determine calibration data for the computer tomography system on the basis of the first set. The first set is further recorded during a first rotation run wherein the computer tomography system and the object to be examined rotate relative to each other, wherein the second set is recorded during at least a further rotation run after the first rotation run. On the basis of the calibration data and the first and second sets a computer tomography recording is reconstructable.