Digital lab
Impose pages into signatures for saddle-stitched magazines or perfect/sewn-bound books, with automatic creep compensation.
Press sheet format
The physical sheet that feeds into the press. It must be large enough to hold all the pages of the signature plus the marks margin around them. For an A4 magazine, A3 or SRA3 are the typical choices. SRA3 adds 23 mm of extra bleed space over A3, very useful for bleed work with crop marks.
Sheet width in millimetres. Example: for a custom SRA3 format you can enter 320 mm.
Sheet height in millimetres.
Creep compensation
Creep is the progressive outward shift of inner sheets in a saddle-stitched booklet: the centremost sheets stick out more than the outer ones. In an 80-page magazine at 90 g/m², the shift can reach 2 mm. Without compensation, inner margins end up uneven in the finished product. The application shifts each sheet by the amount corresponding to its nesting depth.
Paper weight (g/m²) determines its approximate thickness. The application uses a standard conversion table: 80 g/m² ≈ 0.10 mm; 115 g/m² ≈ 0.13 mm; 150 g/m² ≈ 0.17 mm. The thicker the paper, the greater the total creep.
Enter the actual thickness measured with a micrometre. Useful for non-standard paper, board, or specialty stocks. The typical value for 80 g/m² offset paper is 0.10 mm.
Signature type
Defines how each sheet is folded to form the signature pages. F8 (quarter fold): the sheet is folded twice → 16 pages per printed sheet. F16 (eighth fold): three folds → 32 pages per sheet. F32: four folds → 64 pages per sheet. Rows are printed head-to-head (alternately rotated 180°) so that after cutting and folding all pages read the same way.
A signature is a set of pages imposed, folded, and trimmed together to form a self-contained booklet section. The book is assembled by sewing or gluing several signatures together. For perfect or sewn binding, 16- or 32-page signatures are the most common. A 160-page book with 16-page signatures will have 10 sections.
Print marks
Strip around the printable area reserved for production marks (crop, registration, bleed, colour bars). Typically 10–15 mm. Must be wide enough to fit the marks without overlapping the content.
Short lines at the four corners of the sheet indicating where to cut. Essential for the final guillotining. Typically printed 5 mm outside the trim line.
Dashed line in the margin indicating the position of the central fold. Helps the folder operator to centre the crease and verify alignment.
Show how far the bleed extends: the colour area that goes beyond the trim line to avoid white edges if the cut is not perfectly accurate. Bleed is typically 3 mm. Only visible if the source PDF includes bleed (TrimBox different from MediaBox).
Cross-in-circle symbols printed on all four margins of the sheet. They allow the four colour layers (Cyan, Magenta, Yellow, Black) to be aligned perfectly in offset printing. When the crosses stack exactly, colour registration is correct.
A strip of colour patches and grey scales on the sheet margin. The press operator reads them with a densitometer to measure and adjust the ink density of each colour during the print run.
Identifying text that will appear at the foot of each imposed sheet. Useful for identifying the job in the pressroom. If left blank, the PDF filename is used.
Fit: pages are scaled up or down to fill exactly the available space in the signature. Reduce only: pages are scaled down if too large, but a small page is never enlarged. No scaling: 1:1 natural size; ideal when pages are already laid out at the exact finished size.
Duplex printing
Defines how the printer flips the sheet to print the reverse side. Short edge: the sheet flips around the horizontal axis, like turning the page of a notepad; the standard setting for landscape sheets and most booklets. Long edge: flips around the vertical axis, like a wall calendar; typical for presses that do tumble. Always check your printer manual.
Sheetwise: the simplest method. Front and back are imposed in separate files or press passes; two plates or two set-ups are required. Work-and-turn: all front and back content is placed on one plate. Half the run is printed, the sheet is flipped on its side (vertical axis) and the same plate prints again. Result: two booklets per sheet. Work-and-tumble: same as work-and-turn but flipping on the short edge (horizontal axis).
Horizontal correction of the back content to compensate for mechanical registration of the press. If the back appears shifted right, enter a negative value. Typically between −1 and +1 mm.
Vertical correction of the back content. If the back appears shifted downward, enter a negative value.
Gripper and marks
The gripper is the mechanical clamp that grabs the sheet to feed it into the press. The gripper edge is not available for printing: content and marks must stay inside this zone. On folding presses, the gripper is usually the top or left edge of the sheet.
The distance the press needs to grip the sheet reliably. On large-format presses (B2, B1), typically 10–15 mm. In the output PDF it is shown as a dashed red line at the gripper margin.
On a saddle-stitcher, the signature must extend slightly beyond the spine so the stitching mechanism can grip it. This fold extension is called the lap or overfold. Typical value: 3–6 mm. It is shown as purple lines in the output PDF.
Collation marks are black rectangles printed on the spine of each signature, offset progressively from one to the next. When the signatures are stacked in order, they form a diagonal stripe visible from the spine side. If a signature is missing or misplaced, the stripe breaks and the error is spotted at a glance.