Correction of misalignment of nozzles of an inkjet printer

A method of correcting misalignment of nozzles of a multi-colour inkjet printer for printing an image on a printing medium that is movable with respect to the inkjet printer in a conveying direction, the inkjet printer having a plurality of printheads for each printing colour, the plurality of printheads being mounted in a matrix configuration of columns and rows, a printhead having an array of nozzles configured for ejecting ink droplets of a printing colour, wherein either the printheads of the same printing colour are arranged in a column of the matrix configuration extending in a direction parallel to the conveying direction and the printheads for different printing colours are arranged in rows extending in a direction perpendicular to the conveying direction on a carriage that can reciprocate in a scanning direction perpendicular to the conveying direction of the printing medium, or the printheads for different printing colours are stationary arranged in a column of the matrix configuration extending in a direction parallel to the conveying direction and the printheads for the same printing colour are arranged in rows extending in a direction perpendicular to the conveying direction;

• wherein the method comprises the steps a)-b) of:
• printing a test pattern on a test substrate, the test pattern comprising a test pattern section for each printhead;
• scanning the printed test pattern thereby obtaining a scan of the printed test pattern;
• a) analysing the scan for relative positions of droplets, ejected by each of the nozzles of each of the printheads for a reference printing colour, Clr_ref, with respect to a reference element;
• b) analysing the scan for relative positions of droplets, ejected by each of the nozzles of each of the printheads for each of the printing colours, Clr≠Clr_ref, other than the reference printing colour, Clr_ref, with respect to relative positions of the droplets ejected by each of the nozzles of the corresponding printhead for the reference printing colour, Clr_ref;
• c) determining deviations for each of the nozzles of each of the printheads based on the determined relative positions of the droplets, ejected by the nozzles of the printheads, by applying a mathematical function defined piecewise by polynomials;
• and
• d) assigning correction factors to each of the nozzles of each of the printheads of the plurality of printheads based on the determined deviations of the nozzles of the printheads.