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Most complaints in printing do not come from the machine, but from the file that reached it.

Below is a practical guide to preparing artwork for print: what to set, what values to take and why exactly those. The rules are ordered from decisions made at the start of a project to the last check before sending.

File format

The standard for exchanging artwork is PDF, because it carries graphics, text, fonts and colour settings in one file and looks the same at the designer and at the printer. TIFF and EPS are still used, but for particular purposes: the first for raster images, the second in older production workflows.

PDF itself comes in variants adapted to printing, marked as PDF/X. Two are met most often:

• PDF/X-1a requires colour in the print space and flattened transparency. A safe choice when you do not know what software the printer has.
• PDF/X-4 allows live transparency and layers and carries colour profiles. More convenient in a modern workflow, but it requires the other side to support it too.

If the printer names a particular variant in its specification, that takes precedence over any general rule.

Colour

Artwork for offset and digital printing is prepared in the print space, that is in four inks. The screen space describes light, not ink, so leaving it in the file means the machine will decide about the conversion, not the designer.

Three things are worth setting deliberately:

• Total ink coverage, that is how much ink lands in one place. On coated paper the usual limit is up to 300 per cent, on uncoated and newsprint less, because the substrate dries longer and absorbs more.
• Black for text: black alone, without any admixture of the other inks. Text separated into four inks goes out of register at the slightest misalignment of the machine and loses its sharpness.
• Black for large areas: black reinforced with the other inks, otherwise the background comes out grey. Typical proportions stay within the ink coverage limit given above.

Before you send the file it is worth seeing how the critical colours will behave. The CMYK simulation will show which colours from the screen fall outside what the inks can do and what they will be replaced with.

Bleed

Bleed is artwork extended beyond the trim line. It protects against a white strip at the edge when the knife lands slightly off the intended place.

Contrary to a widespread belief, no standard prescribes a particular value. The PDF/X standard defines the document boxes, including the bleed area, but not their size. The number follows from the technology and from how precisely a given printer trims. Typically:

The values in the table are a starting point, not a rule. Some online printers lower the requirement to as little as one and a half millimetres, because they control trimming more precisely. The specification of the printer that will do the job always wins.

Bleed, tolerance and why business cards forgive the least

Here lies a misunderstanding that costs more than a badly set bleed. Bleed and trimming tolerance are two different things. Bleed is a reserve of artwork, tolerance is the actual spread with which the knife hits the line. Bleed must not be smaller than the tolerance, but it is often larger, because the printer keeps a safety margin.

For the look of the finished job the decisive factor is the tolerance, not the bleed. It determines how far the finished copy will be shifted against the design. Take a business card of 90 by 50 millimetres with a frame running 5 mm from the edge:

The same frame can be four times wider on one side than on the other. The eye catches broken symmetry at once, although it rarely manages to name the cause. On a business card a shift of three millimetres is over three per cent of the width, and with a centrally placed mark that is enough to make the whole thing look careless.

Hence three design rules that save small formats:

• Avoid frames and borders running parallel to the edge. Nothing exposes the spread of trimming as clearly.
• Build symmetry inside, not from the edge. An element centred against other elements will absorb a shift, one centred against the edge of the paper will reveal it.
• When centring is critical, ask about the tolerance, not the bleed. These are two different numbers and only the first tells you how the finished copy will come out.

Safe area

The opposite of bleed is the safe area, that is the zone inward from the trim line where nothing important is placed. About 5 mm is assumed, and with a typical tolerance that is a minimum rather than an excess.

You can work out the bleed, the trim lines and the safe area for a particular format in the bleed and margin calculator, together with ready trimmed and untrimmed dimensions to enter in your design software.

Image resolution

The rule of three hundred points per inch applies to material viewed close up: leaflets, catalogues, business cards. On larger formats it is unnecessary, because legibility is decided by viewing distance, not by the number of points alone.

• Print viewed close up, up to A3 format: about 300 points per inch at final scale.
• Posters and boards seen from a few metres: 100 to 150 points is comfortably enough.
• Large format read from a dozen or more metres: even a few dozen points give a correct result.

You can calculate the number of pixels needed for a particular size in the DPI calculator. Remember at the same time that enlarging a small file repairs nothing, because missing information cannot be written in.

Type and fine elements

• Convert type to curves or embed it in the file. Without that, a printer that does not have the same typeface will substitute another and the layout will shift.
• Do not go below six points in positive text, and with light type on a dark background leave more, because the ink spreads into the reverse and closes the counters.
• Thin lines below a quarter of a point can disappear or come out uneven, especially when they are built from several inks.
• Build small text and hairline elements from a single ink. Every additional one increases the risk of misregister at the edge.

Overprint and transparency

Overprint decides whether an element sits on the background or knocks it out underneath. Black text is usually overprinted on the background, so that a slight misalignment of the machine leaves no white outlines around the letters. With white it is the other way round: set to overprint it simply disappears, because there is no white ink in printing, only unprinted paper.

Transparency, shadows and blending modes look different on screen from how they look once flattened for print. If you save the file in a variant that requires flattening, do it deliberately and look at the result instead of leaving the decision to an automated step.

Spot colours

Brand colours chosen from a swatch book do not always have an equivalent in four inks. If the colour is critical, consider printing with a spot colour, and if it is to be separated, check beforehand how far it will move from the reference. Leaving unused spot colours in the file is in turn a frequent reason for surcharges, because for the printer it means an extra plate.

The check before sending

The last step is often skipped, yet it catches most errors. The minimum list:

• trimmed and untrimmed dimensions matching the order,
• bleed on every edge, important elements inside the safe area,
• colour mode and total ink coverage,
• fonts embedded or converted to curves,
• image resolution at final scale,
• the number and order of pages, and in publications also the blank ones,
• no superfluous spot colours and no unused layers.

You can check all of it automatically in our PDF file check, which runs through several dozen rules and points out what needs correcting before the file goes into production.

Summary

Preparing a file comes down to one question: will everything that matters survive the unavoidable imprecision of production. Bleed protects against a white strip, the safe area against content being trimmed off, the right black against a grey background, and the check against a surprise on the pallet with the finished run.

The values given above are a starting point. The specification of the printer that will do the job is always more important, because it is the one that knows its machines and their tolerances.

Preparing artwork and would rather be sure? Take a look at our offer of printing. We will check the files before production and suggest what to correct before the machine starts.