Imposition, broadly defined, is what describes the arrangement of pages on the press sheet so that when folded, the pages will read consecutively. When you decide how to arrange the pages on the sheet, you will base it on the size of the press sheet and the pages, as well as how the job will be folded and bound. The imposition design will also depend, in part, on the binding method to be used.
If you would like to make a mock up of a simple imposition, simply fold a sheet of paper at right angles into the required number of pages and number them while they are still folded. When you unfold them, each page will be in its proper position on the sheet. This will give you an overall idea of the Imposition/signature concept.
The most popular binding methods include Perfect-Binding, Saddle-Stitching and Collate-and-Cut. A good example of Perfect Binding would be a telephone directory. Following printing of the directory pages, they are collated into their proper order and put into a clamp device at the bindery. Typically, about 1⁄8” of the spine edge is removed (cut off), and glue is applied to the spine area as well as a small section over the edge front and back. The directory cover would then be adhered to the glue area.
Saddle-Stitching, on the other hand, would need an example such as a magazine publication, or even a catalog (in some instances). This method of binding is achieved by stapling the pages along a center fold. In preparing an imposition for a saddle-stitched job, you must realize that the pages on a single sheet of paper are not going to be consecutive. Folding the job is what provides a detailed example of a saddle-stitching job. A publication/piece that is bound by saddle-stitching can be easily opened and will lie flat when opened up.
The Collate-and-cut binding method actually includes several types of binding including Side stitch — which means it is stapled along the left side of the pages, Corner stitch — which means it is stapled in the upper left corner, Spiral wiring, GBC and 3-hole binding. Each of these methods actually means that the pages are collated into order and holes have to be drilled or punched once the job is printed and trimmed.
There are printers who do not print both sides of paper in one pass. The printed paper has to be re-fed into the press for the second side. That means that the pages need to be arranged on the plate so that when the paper is flipped for the second pass, the correct back pages print on the back of the front pages.
Your personally selected binding method could designate which process is used, or your printer could have a method they prefer themselves. The three most common methods of printing the second side of a press sheet are Work-and-tumble, Work-and-turn and Sheetwise. To understand the difference in the three, you have to understand how the press sheet is handled after the first side is printed.
A Work-and-tumble layout (below) is equivalent to the Work-and-turn, except that following the printing of the first side of the press sheet, the paper is “tumbled” or flipped from top to bottom. In other words, the left side of the press sheet for the first side printing is the same as the left side of the press sheet on the second side printing.
A Work-and-turn layout (below) means that after the first side of the press sheet is printed, the paper is flipped over side-to-side and fed through the printing press again. Unlike the Work-and-tumble method, when flipping, the top and bottom are not inverted. The top of the first side is the top on the second side.
The Sheetwise method (below) means printing the second side of the paper using a completely different plate. Sheetwise is also used for jobs that only print on one side of the paper. If your press uses a press sheet that is capable of printing 8 pages on a single side and your job contains only 16 individual pages, then you can go with a sheetwise imposition method. It means the press will print the fronts of 8 pages, flip the paper and print the back of those same 8 pages. Your specific job has to consist of enough pages to fill up both sides of the press sheet.
As a designer, understanding and designing with signatures will offer you endless design possibilities.
Where imposition is the arrangement of all the pages in a job, a signature is a unit of organization within that job’s imposition. Jobs with more pages than can print on a single press sheet are comprised of multiple signatures.
For example, an imposition that consists of 8-up signatures means that eight pages are placed in one printable unit, the next eight pages are placed in the next printable unit, etc. Each of the printable units or the pages printed on a single piece/area of paper, is a signature within the imposition. The pages within a single signature may not be consecutive, contingent on the folding and binding defined for the job. The size of the press sheet is dependent on the press itself. Larger presses can print 8, 16, 32, or more pages on one press sheet. Impositions should always make use of the largest standard size press sheet that the particular press can support.
There are many types of layouts that you can opt for. A few examples are 2-Up layouts, 4-Up layouts and 8-Up layouts. A 2-up imposition is when there are two pages on each side of each signature. You could also have a 2-up Work-and-Turn layout in which case the two pages on the front are the same, and the two pages on the back of the signature are the same. For example, side 1 has two page ones and side 2 has two page twos. After printing, the pages are cut apart and you end up with double the number of pages as press sheets.
You could design a 4-up layout to support the Work-and-Turn or Work-and-Tumble printing methods. Using either of these methods, you would end up with two complete pages of each individual page on each press sheet even though the layout is different for each method.
Fold marks, registration marks and color bars
Don’t forget, though, that a press sheet will need to include more than just the pages to be printed. If the sheet needs to be folded, fold marks should appear outside the page area as a guideline. Additionally, all process color jobs will need registration marks as well as color bars to assist the press operator while it’s on the press. Your press sheet should also contain crop and center marks, color/density bars, as well as any pertinent job information. If your job is a black and white job, it won’t necessarily have to have registration marks.
Imposition for printing can reduce paper waste and save money on printing jobs. Imposing pages for printing is not just for commercial printing. Printing a 5.5″ x 8.5″ booklet on your desktop printer, for example, requires the use of imposition to print the pages onto letter size (8.5″ x 11″) sheets of paper that when assembled and folded end up with the pages in the right order for reading.
XChange US offers solutions that let designers and prepress operators quickly impose any type of job. Imposition solutions offer simplicity in creating folded layouts, organizing step-and-repeat jobs, cutting and stacking, and creating perfect-bound books. The available products will allow you to produce faster, more accurate impositions that maximize press sheet usage and make it easy to produce similar or repetitive jobs effectively, efficiently and automatically.