Page 163 - Graphic Design and Print Production Fundamentals

Graphic Design 151

Figure 5.4 cut and stack

Sheet-wise impositions image the fronts of all pages on one side of the sheet and impose all the backs on
a separate set of plates for a press run that will back up all the sheets. Work and turn imposes the fronts
on one half of the sheet and the backs on the other half, with the axis running perpendicular to the grip
of the sheet (see Figures 5.1 and 5.2). Work and tumble imposes all fronts on the bottom half of a sheet
and backup images on the top half of the sheet (see Figure 5.3). The sheets are flipped halfway through
the press run, with the axis parallel to the grip edge of the sheet. Cut and stack imposes the pages so full
press sheets can be collated, and the collated sheets cut and stacked in order on top of each other to make
a final book (see Figure 5.4).

Lithographic web offset presses have imposition orders that depend on how wide the web of paper is,
and how many web rolls and half rolls will be brought together before folding on a first former, and
cutting on a second former. There are many options for configuring a web-fed litho press, depending on
the number of pages in a publication. Usually, the entire publication is printed and folded by running
the stack of web paper together and folding it in half over a former.

Imposition has to account for creep and bottling when imposing for thicker publications. Creep pushes
the image on a page closer in to the spine the further the page is toward the spine, by the width of the
thickness of the publication at the stapled, spine edge. Bottling skews the image on a page to account
for the skewing of web rolls of paper that are folded in very thick signatures. The thicker the folded
signature of a bound book, the more skewing takes place, which should be accounted for in the ‘Bottling’
value in an imposition.

Imposition for inkjet mediums is usually done when the image is rasterized. The RIP will store the raster
image and nest several raster images together to fill the dimensions of the media being imaged. This
is usually set as an automated function in the RIP, and is tied to the size and cost of the media being
used. When imaging very low resolution images on very low cost media, the manufacturer is usually
more concerned with the speed of the machine than the utilization of the media. If an expensive media
is being used, the automatic imposition will be utilized in the RIP to save media. Often inkjet images
are not square, and the media will be die cut or cut with a router after imaging. The RIP can be set to