1. Method of determining the spatial response signature of a two dimensional x-ray detector comprising a photostimulable phosphor by generating a flat field image by homogeneously exposing said detector to radiation and scanning the homogeneously exposed detector and by digitizing the scanned image, generating a low-pass filtered version of said flat field image, demodulating said flat field image by means of corresponding pixel values in said low-pass filtered version characterized in that said signature is obtained by processing multiple flat field images generated for the same detector and said multiple flat field images are spatially registered by applying spatial warping whereby a reference flat field image for said spatial warping is selected such that the maximum angular difference between the pixel matrices obtained by scanning said reference flat field image and any other of said multiple flat field images, is minimal.