Print-ready files: PDF/X, colour and a checklist

Checklist before you upload

1. Size: document size is the trim size plus bleed on every side (usually 3 mm). An A4 flyer is therefore 216 × 303 mm.
2. Bleed: backgrounds and images that run off the edge reach right to the edge of the document.
3. Safe area: text and logos at least 3 to 5 mm inside the trim line.
4. Resolution: images at 300 dpi at their final size, line art at 1200 dpi.
5. Colour space: CMYK. Convert RGB images first, or check whether the printer does it for you.
6. Colour profile: the profile named in the printer’s spec sheet, for example PSO Coated v3 for coated paper.
7. Black: text in pure black (0/0/0/100), large black areas in rich black.
8. Fonts: embedded or converted to outlines, with a minimum size of about 6 pt.
9. Lines: no thinner than 0.25 pt (about 0.1 mm), or they disappear.
10. File format: PDF/X-4 or PDF/X-1a, one file per product, pages in the right order.

PDF/X-4 or PDF/X-1a?

Both are standards for exchanging files in prepress. PDF/X-1a is older and requires all transparency to be flattened and all colours to be converted to CMYK or spot colours. PDF/X-4 allows live transparency and RGB elements with an embedded profile, and leaves the conversion to the printer’s workflow. Most printers now prefer PDF/X-4. If the spec sheet says nothing, PDF/X-4 is a safe choice.

Which colour profile?

The European profiles come from the European Color Initiative (ECI) and can be downloaded free of charge. The question is not which profile is “best”, but that your file and your printer use the same one. The profile also sets how much ink may be laid down in total (total area coverage). For the common profiles, the limit is usually between 300 and 330 %.

Not all black is the same

Text should be set in pure black, using only the K channel (0/0/0/100). If it were mixed from all four inks, the slightest misregistration would leave coloured fringes around the letters.

Large black areas, on the other hand, look a little grey in pure K. For a deep black, other inks are mixed in, for example 40 % cyan, 30 % magenta, 30 % yellow and 100 % black. Many printers specify their own recipe for this rich black.

Spot colours: Pantone and HKS

For brand colours that must be matched exactly, there are spot colours from systems such as Pantone (used worldwide) and HKS (common in Germany). They are mixed as a separate ink and printed on their own. That only works in offset printing and adds a printing plate for each spot colour. Digital presses simulate spot colours from CMYK, and some shades come out visibly different. More on digital and offset printing.

When the printer sends your files back

The usual reasons are missing bleed, images with too little resolution, fonts that are not embedded and files in the wrong format. Many online printers check files automatically and show a preview with warnings. Take that preview seriously: whatever is white there will be printed white.

Frequently asked questions