Imposition refers to the specific arrangement of the pages of a printing form in such a way that the printed and folded sheet results in the correct sequence of the page numbers. The pages must hold register when printing and be in the correct sequence after the sheets have been cut and folded. The imposition scheme results from the format of the print and the type of bookbinding further processing. The most common binding methods are saddle stitching, adhesive binding, thread stitching and loose-leaf collection. Other special processes are also used in the field of web printing.
In the work set, 16 printed pages are usually arranged on a folded sheet, this corresponds to eight pages each in front and back printing . The benefit indicates how many bookbinding sheets the print sheet is used with. If 16 pages are arranged on a printed sheet, this is used once, if 32 pages are arranged it is used twice.
The trim is the margin that is additionally required to be able to trim the book block after printing. The gripper edge of a sheet-fed printing press must also be taken into account.
Furthermore, imposition is a term for the removal of the unprinted interleaf sheets that are placed between the fresh printed sheets against the rest . The insertion of these slip sheets is called shooting in.
The example above shows the page distribution for a 16-page booklet . Eight pages go on the front and eight pages on the back, so that, for example, page 2 is the back (reverse printing ) of page 1. After printing, the paper is first folded vertically (page 2 falls on page 3), then horizontally (page 4 falls on page 5) and finally vertically again (page 9 falls on page 8). The following picture shows the result before binding and trimming:
The position and orientation of the pages on the print sheet is initially dependent on the folding scheme used . The most common folding sequences are two- fold cross-fold ( folded sheets with 8 pages) and three-fold cross-fold (folded sheets with 16 pages). In the case of products that consist of more pages than fit on a printed sheet or folded sheet, the collection process is also important (collection for single or multi-layer brochures ).
Imposition in the production of CTP printing plates is exclusively computer-aided . The imposition schemes for the standard folding sequences are usually permanently stored in the imposition software . Other folding schemes can be stored with the help of folding catalogs, among other things. In the meantime, arranging and aligning the pages can also be solved algorithmically . Well-known computer programs for imposition are ApogeeX (AGFA), Prinect Signa Station (HEIDELBERG), Preps (Kodak), Speedflow Impose and PlugAUTOIMPOSEin (OneVision), GRAPHIAware Nicola (GRAPHIA) or Imposition Publisher (Farrukh Systems). Metrix (Lithotechnics) or KIM (Krause-Biagosch) are especially suitable for collecting shape optimization.
When determining the folding scheme to be used, the direction of the paper , i.e. whether it is wide, narrow or machine web, must be taken into account. This is an important criterion if the printing sheet is to be further processed by folding machines or if individual parts of the printing sheet are to be perforated or punched out. A wrong direction of paper travel can mean that a perfect-bound book cannot be leafed through.
This fold is one of the cross-fold folds like two or four folds. The number of fold breaks is determined by the sheet format, the paper properties such as paper weight or volume, but also by the type of binding. This type of folding is often used in brochure and book production. These are mostly 16-page sheets. If a work cannot be divided into 16 pages, ½ or ¼ sheets are used.
If several sheets of paper have been folded and trimmed, the inside pages will be shorter on the sides. The exact value of this effect - called displacement or increase in bundle - depends on the number of pages as well as the grammage and paper volume of the paper type used. This must be taken into account when designing a brochure (especially with saddle stitching ).
Most imposition software is able to take this effect into account. Here, the pages are indented steplessly by the desired amount towards the center of the folding sheet in the gutter or even completely scaled. However, indenting is not always possible for pages with overflows - also known as defectors , which has to be taken into account when laying out .
The printer uses the color control strip to precisely set the color guide. The individual strips are tailored to different printing machines. They mostly consist of the color fields for the process colors cyan , magenta , yellow and black as well as a different number of special colors and special measuring fields . These fields are measured with a densitometer or with a control strip reader. The values determined are transmitted to the printing presses and correct the ink flow in the corresponding ink zones. Sheets are removed and measured again and again during the print run.
In Flattermarken is markings on the back of the folded sheet. They are used to control the correct sequence of the sheets. Usually, a black line with a size of 2 × 10 mm is used, which is located in the milling edge - i.e. in the spine - of an adhesive binding. For example, the mark of the first sheet is 10 mm from the top of the sheet; the mark of the second sheet 20 mm, that of the third 30 mm, etc .; according to this example always offset by the value of a brand. If you now look at the back of the collected arches, the flutter marks form a staircase. Should an arch be in the wrong position, the stairs would be interrupted. This control process is also called collation.
Registration mark , register mark or short passer referred to a graphical figure, with the fit of each color can be monitored in the overprint. Usually this mark consists of a circle and a cross made of thin lines, similar to a target cross. The registration mark is positioned in exactly the same place in each individual color (CMYK, possibly special colors). During printing, printed sheets are repeatedly checked with a magnifying glass ( thread counter ), now also electronically through optical scanning. This is necessary to avoid the so-called misregistration, the imprecise overprinting of individual printing colors. Misalignments lead to blurring in the image and font display as well as to color deviations or so-called " flashes ".
- Hubert Blana: The production. A manual for the design, technology and costing of books, magazines and newspapers (= basic knowledge of the book trade: Verlag. Volume 5). 4th revised and expanded edition. Saur, Munich 1998, ISBN 3-598-20067-6 .
- Wolfgang Walenski: Dictionary print + paper. Vittorio Klostermann, Frankfurt / M. 1994, ISBN 3-465-02619-5 .