US Patent 7605950 Printing apparatus

A printing apparatus for generating a test chart using a plurality of sheets of printing paper and correction data having high accuracy according to the test chart. Overlapping regions G are extracted from scanning data D1 and D2 of two test charts. Tendency in variation (inclination) of the density is obtained for one set of the scanning data in the overlapping regions G and such tendency in variation is reduced. The scanning data D1 and D2 are then combined together to eliminate the density difference, thereby obtaining a single set of combined scanning data D3. A correction data generation means updates a correction table based on density data of the scanning data D3.