Page 160 - Graphic Design and Print Production Fundamentals

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. Saddle stitching is a binding process that folds the media after it is imaged on both
sides, stacks the printed folded sheets one inside the other, and applies staples to the spine of the book.
The other dominant style of book binding built into copiers is perfect binding. Media is imaged on both
sides and folded, but the folded sheets are stacked on top of each other, glue is applied, and a cover sheet
is wrapped around the glued book to encase the spine. The pages have to be imposed in a completely
different order on the printed sheets. The first and last sheets of a saddle-stitched book are imaged on the

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