A method for calibrating a counting digital X-ray detector includes performing a threshold value scan in at least one defined X-ray spectrum for irradiating the X-ray detector, which includes a matrix composed of pixel elements, storing count rates of the pixel elements as a function of respective applied threshold values, and from results of a measurement of count rates of the pixel elements, determining or calculating individual correction threshold values for the individual pixel elements. The individual correction threshold values correct a threshold value that is to be applied to the pixel elements for the defined X-ray spectrum such that threshold value noise is reduced.