1. A method of evaluating the severity in a printed image of a repeating band print artifact, the method comprising: electronically capturing the printed image to form a captured image; for each of a plurality of patches taken from one or more selected regions of the captured image: producing a spatial intensity profile across the patch substantially at right angles to an expected direction of extent of any repeating band print artifact present in the captured image; applying a Fourier-related transform to the spatial intensity profile and summing the resultant spatial frequency coefficients in a limited range about a frequency of interest to produce a repeating-band-print-artifact severity measure for the patch at that frequency; and determining an overall artifact severity value at the frequency of interest from the severity measures of said plurality of patches.