QUESTION: What is imposition?
ANSWER: Imposition (also known as "page imposition") is the process of
- modifying the position, orientation, and printing order of the individual pages in a document, and
- grouping collections of individual pages together on larger sheets of paper or film so the pages are arranged properly for printing on a particular printing press or digital printer, and (if applicable) for binding with a particular binding system.
To illustrate how imposition works, we give an example of one of the simplest and most common imposition tasks: creating a booklet.
What is a booklet? A booklet is a small book that is formed by printing four individual pages on each sheet of paper (two pages on one side and two pages on the other side), stacking the printed sheets, stapling the sheets in the middle, and then folding them. A booklet is also known as a "saddle-stitched booklet" or "saddle-stitched book."
Although we talk about creating a booklet in this example, imposition is often required when creating other types of documents (e.g., postcards, greeting cards, magazines, calendars, business cards, tickets, and of course, books).
The required arrangement of the pages is dictated by
- the dimensions of the pages in the booklet
- the number of pages in the booklet
- the size of the sheets that will be printed on the press (if a printing press will be used) or on the printer (if a digital printer — such as a laser printer — will be used).
For our example, we'll create a very small booklet. It will have a front cover, a back cover, and six pages inside. In other words, it will have eight pages, counting the front and back covers.
It will be made up of two sheets of paper. Four pages will be printed on each sheet: two pages on the front, and two pages on the back.
When it is finished, it will look like this:
As you read through the example below, don't worry about the mechanics of how you would go about re-arranging the pages. Just concentrate on the concepts that are presented. After we've gone through the example, we'll explain how imposition is handled in real-life situations.
STEP 1: CREATE THE INDIVIDUAL PAGES
We start by creating the eight individual pages. To do this, we can use a word-processing application such as Microsoft Word, or a page-layout application such as Adobe InDesign or QuarkXPress. To save space in this window, we're showing the eight pages side-by-side, in pairs, but you wouldn't create them that way in Word or InDesign or Quark; each page would stand on its own.
STEP 2: PAIR UP THE PAGES IN THE CORRECT ORDER
We must re-arrange the pages so there are two pages side by side on the front of each sheet and two pages side by side on the back of each sheet.
You can see that the pages are not in the normal order in the illustration above. That's because we've arranged them so they'll be in the correct order in the finished booklet.
If you're having trouble visualizing this, take two sheets of paper, stack them, fold them in half, and label the left side and right side of the front and back of each sheet the same way that we've labeled the sheets in our illustration above. Then look at the front and back of each individual sheet. You'll see why we arranged the pages as shown here.
STEP 3: PRINT THE SHEETS
You'll have two sheets of paper.
STEP 4: STACK THE SHEETS
We stack one sheet on top of the other, making sure the pages are in the correct order.
STEP 5: STAPLE THE SHEETS
We staple the sheets together in the middle.
STEP 6: FOLD THE BOOKLET IN HALF
Folding the booklet in half is our final task.
How is imposition handled in real life?
Imposition can be done by hand. That is, you can use scissors and glue to paste two or more individual pages onto larger sheets of paper; then, to create a finished document, you can make copies of the pasted-up pages. Or, if you are working with film instead of paper, you can use special mechanical tools and materials to assemble individual pieces of film into a large sheet of film that can be used to make a plate for a printing press. Then, you use the plate to print the pages on paper.
And for a small project like our example booklet, you can use your authoring application (Word, InDesign, Quark, etc.) to create the pages side by side, in the appropriate order.
But for larger projects, either of these approaches can be cumbersome. That's why most printing companies and other businesses use imposition software to do imposition electronically, instead of doing it manually. Imposition software re-arranges the information inside an electronic file or a collection of electronic files containing a document. With imposition software, you don't need to use glue and mechanical tools.
When you do imposition electronically, your document is contained in PostScript files, PDF files, or perhaps other types of files. These are the files whose information is re-arranged electronically by your imposition software.
In addition to laying out pages on press sheets, most imposition software can do several other tasks, such as:
- printing crop marks to indicate where press sheets should be cut
- trimming pages down to size if they are too large
- re-positioning pages (moving individual pages up, down, left, or right)
- making the text and graphics on the pages larger or smaller
- applying creep adjustments
- adding page numbers or replacing existing page numbers.
Imposition software can be useful even if you are not using large printing presses. For example, many companies use imposition software to create booklets on laser printers.