Image forming apparatus

An image forming apparatus comprising:

• a conveyance unit configured to convey a sheet in a conveyance direction,
• a printing unit configured to print an image on the sheet conveyed by the conveyance unit based on image data, and
• a controller configured to:
• print an image of a first page on a downstream side of a center position of a Nth sheet in the conveyance direction;
• print an image of a second page on an upstream side of the center position of the Nth sheet in the conveyance direction;
• print an image of a third page on an upstream side of a center position of a (N−1)th sheet in the conveyance direction;
• print an image of a fourth page on a downstream side of the center position of the (N−1)th sheet in the conveyance direction;
• perform saddle stitching in which the image of the first page and the image of the third page form a spread, and the image of the second page and the image of the fourth page form a spread;
• perform a magnification correction on image data for the saddle stitching such that a magnification factor of the image to be printed on the first page is equal to a magnification factor of the image to be printed on the third page, and a magnification factor of the image to be printed on the second page is equal to a magnification factor of the image to be printed on the fourth page;
• correct a writing position of the image to be printed on the Nth sheet by the printing unit, based on a toner amount of the image to be printed on the first page and the magnification factor of the image to be printed on the first page after the magnification correction, such that a downstream edge of the image of the second page is positioned at the center position of the Nth sheet in the conveyance direction.