PREPRESS

Prepress for printing and packaging

Everything between an approved design and a plate that prints correctly, and the checks that stop problems reaching the press.

What prepress covers

Prepress is the work that turns a design into something a press can reproduce predictably. Colour separation, trapping, imposition, screening, curve application, plate or cylinder production and the proof that everyone signs against.

Done well it is invisible. Done badly it produces jobs that look correct on screen, pass approval, and then fail on press for reasons nobody can explain at two in the morning.

Where packaging prepress is different

General commercial prepress and packaging prepress are not the same discipline. Packaging adds constraints that simply do not exist on a brochure:

Structure. The artwork sits on a dieline with folds, glue areas and panels that must align once formed, not just when flat.
Technical inks and layers. Opaque white, varnish, cold foil, adhesive patterns and cutting layers all travel in the same file and none of them are process colour.
Substrate. Film, foil, metallised and board behave differently, and white ink under a colour changes its appearance entirely.
Barcodes. Bar width reduction depends on process and substrate. It is one of the few things that can cause an entire delivery to be rejected on arrival.
Distortion. Flexo plates are imaged shorter than the repeat to compensate for wrapping around the cylinder.

Checks worth doing before artwork is released

Dieline. Is it the current version from the converter, on its own layer, set to overprint and not printing?
Bleed and safety. Does bleed extend past every cut and fold, and does critical text sit inside the safe area?
Total ink coverage. Is the heaviest area within what the process and substrate will hold? Use the TAC calculator to check a build.
Separations. Are spot colours real spots or accidental duplicates with slightly different names?
Technical layers. Are white, varnish and foil correctly named, set to overprint, and excluded from the process build?
Images. Effective resolution at final size, correct colour space, no embedded profiles fighting the workflow.
Barcode. Correct magnification, quiet zones intact, bar width reduction applied for the process.
Small text and thin lines. Single colour where possible, never built from four separations on a flexo job.

Why proofs and production disagree

This is the most common prepress complaint, and the cause is usually one of a short list:

The proof was made to a standard the press was never calibrated to
The proof substrate is nothing like the production substrate, which matters enormously on film and metallised material
Measurement conditions differ between the proof and the press check, particularly where optical brighteners are involved
The press has drifted since it was last calibrated, and nobody was measuring

The fix is rarely in the artwork. It is an agreed target, a calibrated press and a measurement routine, which is the subject of G7 colour management.

Frequently asked questions

What is prepress?

Prepress is everything between an approved design and a plate or cylinder that prints predictably: separation, trapping, imposition, screening, curves, plate production and the proof that approval is signed against.

What is packaging prepress?

Packaging prepress adds constraints that general commercial work does not have: a structural dieline, technical layers such as opaque white and varnish, substrate behaviour, barcode bar width reduction and plate distortion for flexo.

What should be checked before releasing packaging artwork?

At minimum the dieline version, bleed and safety, total ink coverage, spot colour naming, technical layers set to overprint, image resolution at final size, barcode magnification and quiet zones, and how small text is built.

Why does the printed job not match the approved proof?

Usually because the proof was made to a standard the press is not calibrated to, or on a substrate that behaves differently, or because measurement conditions differ. It is a process problem rather than an artwork problem.