A method of operating a DR detector including sequentially capturing image frames in the detector that include at least one dark image. The dark image is stored and a statistical measure for a subset of pixels in a captured image frame is compared with the same statistical measure of a subset of pixels in the stored dark image to detect an x-ray beam impacting the detector. An x-ray beam-on condition is indicated if a sufficient difference in intensity between the pixel subsets is detected. At least one more image frame is captured in the detector after detecting the x-ray beam. The current captured image and the at least one more image frame are added and the dark image is subtracted to form the exposed radiographic image.