Bleed, trim and the things paper does

Paper gets cut, and the cut moves

Printing happens on sheets larger than the finished piece, and the stack is trimmed with a guillotine. Paper shifts slightly in the stack, so the cut lands within about a millimetre of where it should — sometimes more.

That single fact produces the two numbers every print job needs:

• Bleed: 3mm. Any colour or image that should reach the edge must extend 3 millimetres beyond the trim line. Without it, a cut that lands 0.5mm outside leaves a white sliver along the edge.
• Safe margin: 3 to 5mm inside the trim. Nothing important — text, logos, faces — within that band, because a cut landing inside eats it.

So an A5 flyer at 148 × 210mm is set up as a 154 × 216mm document with the trim marked at 3mm in from each edge and the content kept 6 to 8mm from the paper's eventual edge.

Resolution, and the distance rule

For anything held in the hand, 300 pixels per inch at final size is the standard. The arithmetic from the cropping lesson: divide pixel dimensions by 300 to get inches.

For large format the requirement drops, because the piece is viewed from further away and angular resolution is what matters. A roll-up banner viewed from two metres is fine at 150dpi; a billboard seen from fifty metres is routinely produced at 10 to 20dpi at full size. A common working method is to build large-format artwork at a fraction of final size — a tenth, say — at 300dpi, and let the printer scale it.

Text and logos should be vector wherever possible, because vectors have no resolution and print at the press's full precision. This is why a logo supplied as a 500-pixel PNG looks soft on a poster and the same logo as an SVG or PDF does not.

Paper changes the design

Weight, in grams per square metre:

 80 gsm   office copier paper
120-170   flyers, leaflets, posters
250-350   business cards, postcards, covers

Finish matters more than weight for how the design looks. Coated stock has a sealed surface, so ink sits on top: colours stay saturated, blacks are deep, fine detail holds. Uncoated stock absorbs ink, which spreads slightly — colours are duller, blacks are greyer, and fine hairlines and small reversed-out text thicken and can fill in.

The design consequences are concrete. On uncoated stock, avoid high-contrast typefaces at small sizes, avoid white text below about 8pt on a dark ground, and expect colours to print perhaps 10 to 15% duller than the same file on coated. If you know the stock in advance, design for it.

Binding eats the inner margin

• Saddle-stitched booklets, folded and stapled, suffer creep: the inner pages push outwards as the stack thickens, so the outer margins of the centre pages get trimmed narrower. The printer usually compensates, and you should ask.
• Perfect-bound books are glued at the spine, and a portion of the inner margin disappears into the curve. Inner margins need to be larger than outer ones — commonly 5 to 10mm more — which is the opposite of what an untrained layout does.
• Spiral and wire binding punch holes, so nothing goes within about 12mm of the bound edge.

Producing the file

The deliverable is nearly always PDF/X, a constrained PDF for print: fonts embedded, colours in a defined space, transparency flattened where required.

• Scribus is free and open source, has full colour management, bleed and trim setup, and exports proper PDF/X. It is the tool to reach for.
• Inkscape handles single-page vector artwork and can export PDF with bleed configured manually.
• GIMP is a raster editor and is the wrong tool for a page layout, though it is fine for preparing the images that go into one.
• The paid industry tools are InDesign, Illustrator and QuarkXPress, and CorelDRAW, which is what a great deal of the Indian print, signage and garment trade actually runs on.

Embed fonts, or convert type to outlines if the printer asks. Outlining guarantees the shapes and makes the file uneditable, so keep an editable master.

Ask first, every time

The single most useful habit in print work: get the printer's specification sheet before you start the layout.

Every printer differs on bleed, on preferred colour profile, on maximum ink coverage, on whether they want crop marks, on how they handle spot colours. Five minutes of asking prevents a re-export the night before a deadline, and printers would much rather answer the question than fix the file.

And for any run above a few hundred, pay for a proof. It costs a small amount, it is the only honest look at how the colour will land on that paper, and it is the step that experienced people never skip.