1. A method for statistically correcting the raw digital data output of a digitizer in a radiography system, prior to Signal-to-Noise Ratio or Noise Power Spectrum calculation, by use of a phantom target having sub-targets which form regions of interest (roi) in an x-ray image of the phantom target, the method comprising: identifying the sub-targets (rois) which have known absorption profiles, the profiles being constant or having a constant gradient; capturing the radiation image of the rois on a detector; converting each pixel of each roi on the digital detector image to dose-linear digital data; and correcting each pixel for non-noise correlated multiplicative artifacts by: 1) multiplying the signal value of a pixel in the roi with the ratio of a roi median value to row median value, or 2) multiplying the signal value of a pixel in the roi with a ratio of a roi median or average value to a column median or average value, or 3) multiplying the signal value of a pixel in the roi with a ratio of a roi median or average value to a row median or average value AND with the ratio of the roi median or average value to a column median or average value, or 4) first splitting the signal value of a pixel in the roi in an effective signal part and a noise part; the effective signal part is then corrected by multiplying with a ratio of the roi median or average value to the row median or average value, the noise part is corrected by multiplying with a square root of said ratio.