1. A computer-assisted method for detecting diaphragm edges in an image, caused by a diaphragm used to gate radiation for producing the image, said image containing said diaphragm edges and other image edges, comprising the steps of: supplying image data representing said image to a computer together with information describing an inner structure of the diaphragm; and in the computer, analyzing said image data for detecting all image edges in the image, and determining said diaphragm images from among the detected image edges using said information.