1. A method of processing a representation of a reference pattern, said method comprising: capturing a representation of the reference pattern, which includes a plurality of features, each of the plurality of features having a different location within the reference pattern; for each of said plurality of features of the reference pattern, determining a location of the feature within the captured representation; based on the determined locations of the plurality of features in the captured representation, calculating a characterization of location transfer error; and applying the characterization of location transfer error to the reference pattern to obtain a spatially modified reference pattern.