In an operating method for a medical installation, in particular an x-ray installation. In activation state of the medical installation, a control and evaluation device determines, upon input of a control command, a useful image of a subject. For this purpose, the control and evaluation device receives raw image of the subject acquired by a detector in a first detector mode, and determines the useful image therefrom on the basis of correction data. In a waiting state of the medical installation, the control and evaluation device updates the correction data for the first detector mode repeatedly after the expiration of a basic time interval since the last driving of the detector. For this purpose, the control and evaluation device receives raw data acquired by the detector and uses it to update the correction data. The control and evaluation device updates the correction data for the first detector mode even in the activation state if, since the last updating of the correction data for the first detector mode, at least an additional time interval has elapsed that is greater than the basic time interval.