5.6 Imposition
Wayne Collins
Imposition of individual graphics page files serves two primary purposes. The first, and perhaps most important purpose, is to utilize media and manufacturing equipment with the most economic efficiencies. The second is to add what has historically been referred to as ‘furniture’ to the manufactured sheet to control processes. We will discuss both priorities for each primary imaging technology we are examining in this book. There is also a range of equipment capabilities for each technology that affects how documents are imposed. There are a few ways to impose the files either pre-RIP or post-RIP. We will also look at ways of imposing in graphic creation software and in specialized imposition software.
The first technology we will look at is electrophotography, where imposition is perhaps the most underutilized. Electrophotographic, or Xerox-type copiers are usually used for short-run lengths with demands for instant turnaround. Duplexing is the simplest type of imposition, but there are four choices for how to orient the back of a single page on the front. The duplexing style can be specified in the print driver, in the PDF file, or in the RIP. Most small printers will turn on duplexing, rather than image the fronts, turn the printed paper over the right way, and image the back of the sheet. Fewer will take the time to utilize the machine and media capabilities to step and repeat an image two up on a larger sheet to half the run time. Yet, as a manufacturing process, electrophotography is the slowest technology for image reproduction, and the most in need of saving time. There are simple rules of automation that can be programmed in a RIP to automatically impose if a run length is over 100 copies. For example, letter-size documents are the most often imaged on this type of equipment. If run lengths of more than 100 copies were imposed two up on a tabloid sheet, it would halve the run time and open up more imaging time on the machine. This introduces another process — cutting the sheets in half before final delivery. Management can determine how well the imaging engine run time is utilized and when it is efficient to have the same operator cut printed sheets in half. Making that management decision requires a knowledge of workflow options for efficiency. Those efficiencies are the primary purpose of implementing imposition software.
Using a ‘step and repeat’ or ‘duplexing’ imposition of single-page file is the simplest example of imposing files for electrophotographic workflows. More and more copiers have capabilities to fold and bind the finished product ‘inline’ in one continuous process. This process is driven by imposing the single-page files in the correct order as they are processed in the RIP, so they image in the proper spot on the media to fold, and bind together in the correct order.
Imposing page files for binding styles usually follows two types of machine capabilities: saddle stitching and perfect binding