To improve the image quality of X-ray images recorded by way of flat detectors, a method for non-linear image processing is provided. An X-ray raw image which is read from a pixel matrix is converted to an X-ray image, wherein the pixel matrix contains pixel elements of a bit depth which is considerably less than the number of pixel elements. A final value is determined for each raw value and can be calculated by use of a non-linear image processing algorithm. Table values are called up and used at least in some cases for the determination of the final values. The table values are associated in a table with corresponding bit values, the maximum number of which is defined by the bit depth.