Why re-invent the wheel ? There is off the shelf applications doing this and much more. Like opening a mulitpage PDF/TIFF to separate pages and vice verca. Even scan all pages of a A4 magazin in a feeder duplex as A3, rotation the images, split the pages, reorganize the pages to readable book, do changes on the pages, and running in reverse and priint duplex on an A3 MPF so you have it back. And anything else you like