A computed tomography system has an x-ray source, x-ray detector, a gantry, and a controller configured to automatically initiate an air-calibration using the source and detector with air in an air space and to determine gain values for channels of the detector from the automatically initiated air-calibration. A computed tomography system having a patient bore, a controller, an x-ray source, and a detector is calibrated by receiving a setting for a medical scan to be performed by the computed tomography system for a particular patient, the setting being one of a plurality of optional values, scanning air and not the patient in the patient bore with the source and the detector using the setting, determining a gain value based on the scanning with the setting and not the other optional values, and scanning the patient with the source and the detector using the setting and the gain value.
