1. A method for non-linear image processing, comprising: calculating table values using at least one portion of a flat-field correction non-linear image processing algorithm, the table values being associated in a table with corresponding bit values, a maximum number of the bit values being defined by a bit depth; storing the table values in a storage medium; reading an X-ray raw image from a pixel matrix; calling up the table values from the storage medium; and converting at least one raw pixel value of the X-ray raw image to a final pixel value of an X-ray image with a correction unit by calculating the final pixel value using the flat-field correction non-linear image processing algorithm and at least one of the table values, the at least one of the table values substituted in the calculation for the at least one portion, wherein the pixel matrix contains pixel elements of a bit depth which is considerably less than the number of pixel elements, the flat-field correction non-linear image processing algorithm is a polynomial function, the at least one portion is less than all of the flat-field correction non-linear image processing algorithm, and each of the table values is derived from a term of the polynomial function.