Image inspection of printed matter with a master image

An image forming system comprising:

• an image forming unit configured to produce a printed matter by forming a second image additionally on a sheet on which a predetermined image has been printed in advance;
• an image scanning unit configured to generate a first image by scanning the sheet and generate a scanned image by scanning the printed matter;
• an image obtaining unit configured to obtain the second image;
• a first registration unit configured to determine a first registration shift amount of the first image based on a difference in pixel values in a first reference area of the first image and the scanned image;
• a second registration unit configured to determine a second registration shift amount of the second image based on a difference in pixel values of a second reference area of the second image and the scanned image;
• a combining unit configured to generate a master image by relatively moving the first image and the second image based on the first registration shift amount and the second registration shift amount and combining the relative moved version of first image and the second image into the master image;
• and
• an inspection unit configured to inspect the printed matter by comparing the scanned image against the master image.

An image inspection method comprising:

• obtaining a first image generated by scanning a sheet on which a predetermined image has been printed in advance;
• obtaining a scanned image generated by scanning a printed matter produced by printing a second image additionally on the sheet;
• obtaining the second image;
• determining a first registration shift amount of the first image based on a difference in pixel values in a first reference area of the first image and the scanned image;
• determining a second registration shift amount of the second image based on a difference in pixel values of a second reference area of the second image and the scanned image;
• generating a master image by relatively moving the first image and the second image based on the first registration shift amount and the second registration shift amount and combining the relatively moved version of first image and the second image into the master image;
• and
• inspecting the printed matter by comparing the scanned image against the master image.