Patent ID: 7760370

Claim:
A method of correcting image forming positions on both sides of a wide paper sheet with a wide size which is greater in size than a maximum image reading size of an image reading system, comprising the steps of, setting image data to form a plurality of reference images on one side of the wide paper sheet, forming a plurality of reference images for positioning on at least an upper end portion and a lower end portion on each of obverse and reverse sides of a first wide paper sheet with the wide size based on the image data and an image forming reference position, folding a middle portion of the first wide paper sheet to make the first wide paper sheet smaller than the image reading area so as to maintain the plurality of reference images on the obverse side of the folded first wide paper sheet and the plurality of reference images on the reverse side of the folded first wide paper sheet, reading the plurality of reference images on the obverse side of the folded first wide paper sheet so as to obtain small-sized obverse side image data through the image readable area of the image reading system reading the plurality of reference images one the reverse side of the folded first wide paper sheet so as to obtain small-sized reverse side image data, obtaining positions of the plurality of reference images on the obverse side of the first wide paper sheet with the wide size based on the small-sized obverse side image data, obtains positions of the plurality of reference images on the reverse side of the first wide paper sheet with the wide size based on the small-sized reverse side image data, obtaining an amount of misalignment between the positions of the plurality of reference images on the obverse side of the first wide paper sheet and the positions of the plurality of reference images on the reverse side of the first wide paper sheet, and adjusting an image forming position on an obverse side of a second wide paper sheet with the wide size relative to an image forming position on a reverse side of the second wide paper sheet according to the obtained amount of misalignment.