1. A method for generating 3D x-ray image data of a subject, comprising the steps of: acquiring a plurality of initial 2D x-ray images of a subject respectively from different viewing directions; producing a plurality of noise-filtered 2D x-ray images by, for each noise-filtered 2D x-ray image, combining at least two of the initial 2D x-ray images with noise-filtering; and generating 3D image data from said plurality of noise-filtered 2D x-ray images.