1. A method for generating 3D x-ray image data of a subject, comprising the steps of: with an imaging system, acquiring a plurality of initial 2D x-ray images of the same subject by irradiating the same subject from a plurality of different directions, so each initial 2D x-ray image in said plurality of 2D x-ray images is obtained from a different viewing direction; from said plurality of initial 2D x-ray images, forming 2D x-ray image pairs, each 2D x-ray image pair comprising a different subset of at least two of said plurality of 2D x-ray images and supplying the two images in each pair respectively to two inputs of a noise filter; in said noise filter, noise-filtering each image pair by combining the respective 2D image therein to produce a single noise-filtered image therefrom, thereby producing a plurality of noise-filtered images respectively from said plurality of image pairs; for each noise-filtered image in said plurality of noise-filtered images, assigning a viewing direction thereto that is the respective viewing direction of one of the 2D x-ray images in the pair from which the respective noise-filtered image was produced; and in a processor, reconstructing 3D image data from the plurality of noise-filtered images, using the respective viewing directions assigned to the plurality of noise-filtered images, and making said 3D image data available at an output of the processor in a form allowing display of a 3D image of the subject represented by the 3D image data.