1. An angiography system for an angiographic examination on an examination object of a patient, comprising: an x-ray emitter attached to an end of a C-arm; an x-ray detector attached to another end of the C-arm; a patient support couch for supporting the patient; a system control unit; and a monitor, wherein the system control unit is configured to: detect a reference image that is adapted to a different or a changed imaging geometry of the angiography system, register the reference image to the C-arm, segment the examination object in the reference image if necessary, generate a mask image from the reference image with image regions lying within the segmentation being contrasted, and subtract the mask image from fluoroscopy live images acquired by the angiography system without administrating contrast agent, and generate a roadmap image from the subtraction, and wherein the roadmap image is displayed on the monitor.