Documentation

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Reduction of creeping pages

Applies only to the imposition of saddle stitching.

In every publication about a saddle-stitching, there is the phenomenon of page creeping. The closer to the center of the publication, the larger the projection. It is caused by the fact that the wire stitch directly touches only the card with the cover (the first), while the other cards are offset from the staple by the sum of the paper thickness of the previous cards.

This phenomenon causes undesirable effects in some publications. One of them is the effect of creeping, for example, page numbering. Printing requires, for example, pagination "to fall on each other", i.e. that the printed page numbers on subsequent pages should be at the same distance from the edge of the page.

The Impozycjoner program has the ability to reduce this effect by moving the image of the page to be impositioned by a distance calculated for each side. The figure below shows a 16-page notebook. After turning on the reduction, we should ultimately achieve such an effect as in the figure below. For comparison, the version with reduction of the extension and the version without reduction, before cutting the edges and after cutting.

Adding H value manually

The distance for which pages will be moved, is calculated according to the formula below:

4-Pages * (H / Number of 4-Pages)

Where "4-Pages" is the number of the next cards and the "Number of 4-Pages" is the total number of 4-Pages in the publication. The cover is not counted.

Calculating H value based on the number of pages and the thickness of the paper

The distance for which pages will be moved, is calculated according to the formula below:

(Paper thickness (number of pages \ 4) – 1)) Coefficient of “sewing quality”

where Coefficient of “sewing quality” is experimentally selected correction (usually 1.2 to 1.4) "quality of staple compression" – ideal value is 1.



Methods of reduction

CROPPING: the width of each page to be impositioned will be cut (trimmed) by the calculated value appropriate for a given page.

SCALING: the width of each impositioned page will be calibrated (reduced) by the calculated value, appropriate for a given page.

Reduce or not (CROPPING)?

The final effect of reducing the cone does not depend only on the proper imposition. Also from the accuracy of card trimming, precision and sewing quality. It may happen that, despite the reduction of the projection, the final effect will be far from satisfactory.

Not every publication is suitable for impositioning with cone reduction. Moving the page to the back causes its content to override the content of the page lying next to it. Therefore, in addition to shifting, you must cut the overlapping part. And in the case when the project assumes the presence of elements passing from page to page through the center (e.g. photos on spreads) can cause unexpected effects (see pictures below) with the TRIMMING method selected.

Moving pages also reduces the necessary bleed, therefore, when designing such a publication, it is necessary to predict much higher values for bleeds - preferably with a sum equal to the normal values of the bleed + the maximum value of the projection (H).

The drawings below show: what is the risk of taking into account the reduction of creeping pages in the publication unadapted. This is a picture of the middle pages of a 16-page publication. In addition to the deformation of the photos placed on the spread, they appear on problems with bleeds. The slope in the examples below was set to 3 mm, while the maximum extension (H) was defined as 4 mm (of course, it is an example value, it is only about approximation of the principle).

This text is also available in German (Impozycjoner.de) and in Polish (Impozycjoner.pl).

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