Patent ID: 7891757

Claim:
A method of measuring a relative offset between a first array of marking elements and a second array of marking elements in a printer, the method comprising the steps of: printing a target by printing a first group of pixels using a plurality of marking elements from the first array and printing a second group of pixels using a plurality of marking elements from the second array, the relative offset being along an offset direction, the target including a first end, a second end, and a center that is positioned midway between the first end and the second end, wherein printing the target including the first group of pixels and the second group of pixels further comprises: printing a reference pattern including a plurality of first regions spaced apart from one another along the offset direction using the plurality of marking elements from the first array; and printing a registration pattern including a plurality of second regions successively incrementally displaced along the offset direction from the plurality of first regions using the plurality of marking elements from the second array such that a degree of overlap between the plurality of first regions and the plurality of second regions varies along the target, wherein the optical characteristic varies according to the degree of overlap; scanning the target to measure an optical characteristic of the target as a function of position along the target; identifying a position at which an extreme in the optical characteristic of the target occurs; and comparing the position of the extreme in the optical characteristic to the position of the center of the target.