Digital compensation method and apparatus using image-to-image distortion map relating reference mark grids

An apparatus comprising:

• a first print engine that prints a first set of reference marks on one side of a substrate;
• a second print engine that prints a second set of reference marks on the same side of the substrate;
• an image sensing unit operative to sense both sets of reference marks on the substrate to generate a digital image of the reference marks;
• a distortion determining unit operative to determine distortion between the print engines based on analysis of the digital image of the reference marks, wherein the distortion is represented by an image-to-image distortion map comprising an array of distances relating to a grid formed by the second set of reference marks to a grid formed by the first set of reference marks;
• and
• a distortion compensation unit operative to generate a digital image that has been compensated to reduce registration errors between images produced by the first print engine and second print engine through the use of the distortion determined from the reference marks from the two print engines.

A non-transitory computer readable medium

• storing instructions that, when executed by a computer, cause the computer to perform a method comprising:
• printing a first set of reference marks on one side of a substrate with a first print engine;
• printing a second set of reference marks on the same side of the substrate as the first set of reference marks with a second print engine;
• sensing both sets of reference marks on the substrate with an image sensing unit and generating a digital image of the reference marks;
• performing image analysis on the digital image to obtain an image-to-image distortion map where the image-to-image distortion map a is local measure of difference between the first set of registration marks and the second set of registration marks, wherein the image-to-image distortion map consists of an array of distances relating a grid formed by the second set of reference marks to a grid formed by the first set of registration marks;
• and
• generating a compensated digital image by using the image-to-image distortion map to reduce registration errors when using the first and second print engines.