Imposition

Are you on the right page?

When we pick up a magazine like Print Media Management we naturally read from page one through to the end, without sparing a thought for the way the pages are ordered when the job is printed. The process of IMPOSITION describes the way we arrange the pages on the printed sheets, so that when the book is folded and bound we find page 2 is opposite page 3 and that all the pages are the right way up.

While the press size dictates the number of pages in a single section, the bindery has most influence on the actual page arrangement, because of restrictions on folding and the gutters and trims needed between and around pages and on the sheet edges. Software that can digitally impose documents takes this into account. Simple flat or folded jobs also need to be efficiently laid out on the sheet to reduce wasted paper and running time on the press. Imposition and layout is therefore a key operation for just about every printed job, and one that can dramatically affect profitability. It is not adequately handled by simply arranging pages on a large sheet with a page layout application.

Let’s look at a simple bound publication, 56pp of A5 text within a 4 page cover, a total of 60 pages. Assume the job will be printed on a B2 press. The cover is printed on a heavier stock, and laminated, so must be handled separately from the text. A publication like this could be saddle stitched, where all the pages are inserted sequentially, or perfect bound where individual sections are stacked alongside each other and glued into the cover.

Binding method affects the layout of the pages in each section or signature. In a saddle stitched format page 1 of the text, p3 of the document, needs to print opposite page 56, p58 of the document, while in a perfect bound book with a series of 16-page sections, p3 prints opposite p18.

For binding, pages are normally arranged head to head, so pages at the top of the sheet are upside down compared to those at the bottom. The designer, oblivious to your requirements, simply gives you a 60 page document in reader order, or possibly worse, with the cover separate but as a spread with no spine allowance. Allowances for folding and the effects of binding are important. The more pages there are in a section, and the thicker the paper, the greater the influence of creep. Centre pages are pushed outwards and compensation needs to be applied to the page content, pushing it inwards towards the spine, to avoid trimming off important matter, like folios, close to the fore-edge.

To best understand how simple imposition works, fold a sheet of paper to represent a section of the finished publication, stack or insert the sections and then number the pages sequentially in reading order. When you open out the paper you will find the key to arranging the pages on the sheets. While present day imposition software saves drawing out the imposition and takes a lot of the hard work out of the subsequent operations, automatically backing up sheets and handling the sequence of pagination, a folded dummy is an essential first step and is your only check, before printing, that the software got it right.

Digital imposition has been around for 20 years and major manufacturers update regularly to cater for new page layout options, as there are often idiosyncrasies in the way a particular application outputs its print file. PDF is now the most common means of supplying the publication content to a printer, but not all PDF files are of equal quality, so preflighting, a computerised health check on the file, becomes essential.

Imposition is increasingly being integrated into the pre-press workflow, so automatically choosing an appropriate layout becomes more important, with JDF and XML providing the tools to intelligently handle the process. Demands from digital printers, for low-cost solutions that can simplify or automate imposition appropriate for their sheet size, run lengths and turn-round times is also making new demands on the software, and increasingly the work is being done by operators with no tradition of dealing with imposition, and little technical appreciation of the requirements.

Choosing your Imposition application

Press size will usually dictate if a ‘Lite’ version of an application is suitable, as the lower cost applications often have a page limit or a restriction on the size of the output format. Some, especially plug-in applications, are also limited by the file types they can accept as input. Mainstream programs will offer more features, but at a higher price, and are often overkill for smaller printers with B2 and smaller presses, or those handling only digital work. However, some features may be essential for the particular type of work you undertake. There are basic differences between sheet fed and web presses, so always make an accurate assessment of your needs against the features and if possible test drive the applications before purchase, most will have a limited time demo available.

If your needs are simple, or only affect a proportion of your business, and you have a PDF workflow, look at some of the plug-ins to Adobe Acrobat, like Quite Imposing Plus, or basic applications with limits on output format, like Metrix X-8 or Impostrip OnDemand. If you have a JDF capable MIS, a link to your imposition, avoiding re-typing job information can be a time saver and improves accuracy. Metrix, Preps and Impostrip all accept Job Intent as JDF, a first step in partially automating the imposition process. Some layout calculators, like Metrix or UpFront, can feed JDF information back to update the MIS with the results of the imposition.

For greater automation you may need to provide a flow of pages with all the content checked, pre-flighted, colour corrected and sorted into order, something outside the scope of most imposition applications, but possible with a workflow manager like Gradual’s SWITCH in combination with common third-party desktop tools, or with a proprietary workflow solution. You then need a hot-folder driven imposition solution. Impostrip products have that facility and use dynamic templates that adapt to the incoming document page size and extent. Quite Hot Imposing is a new standalone application that also integrates with SWITCH.

Ganging several jobs together on the same sheet will save plates, make-ready, running time and paper. Some products, like the Mac version of Preps, can be driven by a script to provide automated fixed impositions for uniformly sized ganged elements like business cards, and the latest Mac version of Preps Pro includes a more flexible ganging feature. For efficient, complex ganging of multiple products, where size and quantity varies, Metrix works well for both litho and large format POS printers, and can generate cost savings in excess of 20%.

For the specialist, Pandora provides the step and repeat required for packaging and labels, locking one-up PDF artwork onto a multi-up cutter die file and controlling the bleeds to avoid overlaps. Book producers could usefully investigate Impostrip BookStacker, enabling economic multi-up, on-demand book production on digital presses, or the CardStacker application will cater for volume production of business cards and social stationery.

The final output file that goes to CTP or your digital press, may be a fully imposed PDF, with all the necessary trim and register marks, colour bars and slug line in place, or increasingly a job ticket describing digitally how the content is arranged and simply providing the layout geometry with the required marks, allowing up to date content to be called in at the RIP. Proprietary workflows may use PJTF for this, but the move is now towards using JDF to drive the process on the RIP.

Imposition may not be one of the flamboyant areas of pre-press that frequently makes the news, but it has a vital contribution to play in producing print profitably.