Bleed, trim and safe zone: a tolerance problem, not a rule
Printed sheets are trimmed in stacks by a guillotine, and paper moves: cutting tolerance is a physical fact of the finishing room. Bleed exists so that when the cut lands a fraction off, the knife still lands on your artwork rather than on white paper; the safe zone exists so it never lands on your text. Australian printers' own artwork guides consistently ask for 3mm of bleed on small-format work and keep-clear margins inside the trim (for example Same Day Printing's guidelines and Optima Press's artwork page). Note what that is: a converged convention printers publish themselves, driven by guillotine tolerance. There is no ISO standard for bleed margins, and anyone citing one is improvising.
Resolution: what 300dpi is actually about
Halftone printing rebuilds photographs from dot patterns, and the press can only render the detail the file carries. The trade convention of roughly 300 pixels per inch at final printed size for sharp viewing-distance work (again: printers' published guidance, not a formal standard) exists because beyond it the halftone screen cannot use the extra data, and below it images soften visibly. Two corollaries the checklists rarely explain: scaling an image up in layout divides its effective resolution, and large-format work viewed from metres away tolerates far lower resolution than a business card held at arm's length. Vector artwork (logos, type) has no resolution and survives any scaling; that is why printers beg for vector logos.
Colour: RGB, CMYK and what the profile is doing
Screens make colour with light (RGB); presses make it with ink (CMYK), and the CMYK gamut is smaller. Something has to translate, and that something is colour management via ICC profiles, the vendor-neutral system maintained by the International Color Consortium (standardised as ISO 15076-1). A profile describes how a specific device reproduces colour, letting your file's colours be converted predictably for a specific press condition and stock type. Practically: work to the profile your printer nominates, convert deliberately (or supply PDF/X with the intent embedded, below), and never let saturated RGB blues and greens reach the press unconverted and unexamined; they are the classic "looked great on screen" casualties. Out-of-gamut brand colours are their own decision (spot versus extended gamut).
PDF/X: the part that is a real standard
Print-ready file exchange is governed by the ISO 15930 family, better known as PDF/X; the PDF Association's overview is the readable map, and ISO's catalogue pages document each part (15930-1, 15930-4, 15930-7; the texts are paywalled, so we cite the descriptions). The idea is constraint: a PDF/X file forbids the ambiguities that break jobs (missing fonts, unmanaged colour, stray RGB) and embeds an output intent naming the intended print condition. PDF/X-1a is the strict CMYK-only veteran; PDF/X-4 (ISO 15930-7) is the modern default, allowing live transparency and colour-managed workflows. Which one to export is your printer's call, not a philosophy debate: ask, and use their joboptions preset if they offer one.
The pre-flight checklist
- Document at final trim size, 3mm bleed on every edge, no text or logos inside the safe margin.
- Images placed at (or near) 100 per cent scale, effective resolution adequate for viewing distance; logos as vector.
- Colour converted to, or managed against, the printer's nominated profile; spot colours defined as spots only if the job is genuinely printing them.
- Black text as 100K, not four-colour rich black (crisp text, no register risk; see register); large black panels per your printer's rich-black recipe.
- Fonts embedded (PDF/X forces this), exported to the PDF/X version your printer asks for.
- One last pass with the printer's own artwork guide, because their kit, not this page, is the contract.
Mini glossary (the terms that cause the phone calls)
| Term | Meaning |
|---|---|
| Bleed | Artwork extended past the trim line so cutting tolerance never exposes bare paper. |
| Trim/crop marks | Fine lines outside the page showing where the guillotine should cut. |
| Safe zone / margin | Keep-clear area inside the trim for anything that must not be clipped. |
| Overprint | Printing one ink over another instead of knocking it out; black text usually overprints. |
| Knockout | The underlying inks removed beneath an object so it prints on clean paper. |
| Rich black | Black built from multiple inks for deep solids; wrong for small text. |
| Output intent | The PDF/X field naming the print condition (profile) the file was prepared for. |
| Imposition | Arranging pages on the press sheet so they fold and trim into the right order. |