Imposition is the arrangement of individual pages or cards onto press sheets, also known as parent sheets. Operators use imposition software to translate PDF files into a format and layout that can be engraved onto printing plates that will be installed into the offset press.
The most typical layout is to have 8 pages per side of a parent sheet, meaning each parent sheet will have 16 total pages when printed on both sides. That said, small-format projects (6″ x 9″ or smaller) may have 16 pages per side of a parent sheet, and large-format projects (larger than 9″ x 12″) may only have 4 pages per side.
Here you can see how a typical 16-page section of a book is laid out for printing. This parent sheet will be folded to the size of the final project, and this grouping of pages is known as a signature. Proper pagination will ensure that the folding process ends with all pages upright and in order.
Playing cards work the same way, there’s an optimized card count for each card size and card stock. Card stock (Blue Core, Black Core, Coreless) parent sheets come in different sizes, which affect how many cards can fit on one sheet, plus the variety of card sizes (Poker, Tarot, Square, Mini).
After imposition, each full parent sheet of artwork is then printed with a large-format proof printer. These high-end printers produce reliable colors that press experts use to color-match against the offset printed sheets.
The operator will also use this sheet to check for pagination, or the order of pages, by folding the parent sheet to final-product size. This process confirms that all the pages will be printed in the proper order and that they will appear right-side up when bound together.
Pagination is not as simple as 1,2,3. This process has rules and algorithms for deciding where page breaks fall. Although most printers use computer systems to automate pagination, sometimes a press operator will override the computer to manually adjust the pagination as needed.
Find a piece of paper and fold it in half three times. Notice how each time you make a crease, you increase your page count by four? This folded sheet is how your pages will be inserted and bound into your book as a unit. It’s also why page counts must be in multiples of 4.*