You work alone, with no DTP backup, and the entire responsibility for the file rests on you from the first click in Illustrator all the way to sending it off. If something goes wrong, nobody will catch it before it hits the press. In an agency or production department someone might still review it. A freelancer does not have that luxury - which is exactly why this article exists.
There will be no theory here about what CMYK actually is. Instead, you get a list of things to physically check, in the order worth checking them, with an explanation of why this particular thing, rather than something else, most often derails projects at the prepress stage.
Why you have to do this yourself in the first place
Because nobody at the printer will guess what you meant. The machine operator sees the file as it is - they do not see your intention, they do not know that the white stripe at the edge was supposed to be background, not an accidental layer mistake. Prepress at the printing house checks the technical correctness of the file, but it does not fix design errors for you, because that is not its role, and it simply does not have the authority to do so without consulting you. If something looks suspicious, you will get a call or an email asking about it - and that is the best-case scenario, because it means a delay, not a ruined print run.
I once sent a poster without bleed myself, because I designed it in a rush and simply forgot. The difference between what was supposed to come out and what actually did was white stripes on two sides, which I only saw after picking up the finished batch. I learned this the hard way, and ever since then I have had a fixed ritual of checking before the file even reaches the export folder.
File format - what the printer actually wants to receive
The safest choice is a flattened PDF, ideally in the PDF/X-1a standard, or a correctly prepared composite PDF. This is a format that locks in all fonts, colors and graphics within a single file, so there is no chance anything shifts along the way because someone did not have the same font installed as you.
Sending a native file straight from InDesign or CorelDRAW is asking for trouble - the software on another computer may reflow the text differently, swap the font for a substitute, or lose the link to an image that was sitting on your desktop. PDF eliminates this problem, because everything is already sealed inside.
For select applications, mainly simpler jobs or single graphics, TIFF and JPG formats are also acceptable, but that is the exception, not the rule. If you are not sure which format fits your job, ask the printing house before you start exporting - that is five minutes of conversation that will save you re-preparing the file.
One tip before you go further: When exporting a PDF from Illustrator or InDesign, always use the ready-made PDF/X-1a or PDF/X-4 preset, not the default screen settings. These are two different worlds, and mixing them up is one of the most common causes of complaints.
Bleed and safety margin - two different things people mix up
Bleed is an extra piece of background extending beyond the cut line, standard 3 mm on each side for catalogs, brochures, books, labels and packaging. It exists because no guillotine cuts with micron precision - sheets in a stack shift microscopically, the blade has its own tolerance, and without this extra margin a thin white line will appear at the edge where the background should reach all the way to the border.
Net format is the final dimension of the finished piece after trimming. Gross format is the net format plus bleed on all sides. For an A5 flyer, meaning 148 by 210 mm, with a 3 mm bleed on each side the gross format comes out to 154 by 216 mm. Background, photos and colored areas must reach exactly to this larger, outer edge - not to the cut line, but beyond it.
Safety margin is a completely different matter, and this is where confusion begins. It is the space measured from the cut line inward, where there should be no text or important graphic elements such as a logo or phone number. The minimum is 3 mm, and for catalogs, brochures, folders, packaging and multi-page jobs it is better to leave 5 mm or more, since there is an added risk of shifting during folding or binding, not just cutting.
Without bleed you get a white line at the edge, because the machine did not hit the contour of your background perfectly. Without a safety margin you get text that is cut off or sits dangerously close to the edge, because even a millimeter of cutting shift can eat into a letter. These are two different problems, two different dimensions, and two different reasons why they exist in the first place.
Net format for A5 is 148×210 mm. With a 3 mm bleed on each side, the gross format is 154×216 mm - background and graphics must reach this outer edge. You measure the safety margin from the cut line (meaning from the border of the net format) inward, minimum 3 mm, and for multi-page jobs 5 mm is better.
A typical mistake: a white frame instead of real bleed
We have already seen files where, instead of extending the background into the bleed, someone left a white frame around it, thinking that was the bleed. The effect is the opposite of what was intended - instead of protection against a white line, you get a guaranteed white frame visible on the finished product, because that frame simply gets printed. Bleed is a continuation of your design beyond the cut line, not empty space.
Image resolution - when 72 dpi is too little, and when it is enough
For offset and digital printing at 1:1 scale you need 300 dpi. That is the standard that ensures fine details, gradients and contours do not blur in print on paper, where pixels are much more visible than on a monitor.
An image taken from a website is usually 72 dpi, because that is enough for screen display - a screen needs a much lower dot density for good image perception than print viewed up close. Enlarging such an image to A3 poster size without recalculating the resolution ends up in pixelation visible to the naked eye, even for someone who has never worked in printing.
The exception is large format viewed from a distance, for example a banner or citylight display - there, 150 ppi is enough, because the viewer looks at it from several meters away, not from reading distance. The rule is simple: the closer the viewer looks, the higher the resolution that must be maintained.
Check this before you export the file: In Photoshop or InDesign, check the actual resolution of the image at the size it will be printed - not the size you received it from the client. An image placed at 100% of the printed format and showing 300 dpi is one thing. The same image enlarged by 300% loses resolution proportionally, landing around 100 dpi, which is already noticeable.
CMYK or RGB - why this is even an issue
The production standard in printing is CMYK, not RGB. If you are working in RGB mode, because that is how the file opened or how you imported the image, you need to convert it before sending, otherwise the printing house software will do it for you automatically, usually with a worse result than if you had done it deliberately in your own software and could correct the colors by hand.
RGB has a wider color gamut than CMYK, especially in neon shades of green, blue and orange. After conversion these colors become more muted, because printing ink physically cannot reproduce what a backlit screen can display. That is not a printing error - it is a limitation of ink physics on paper.
Special colors and Pantone are possible for selected jobs, but they require prior arrangement with the printing house, because that is a separate production process from standard four-color printing. If a design has a logo in a specific, precisely defined brand color, it is worth flagging this before sending the file, rather than counting on CMYK landing perfectly on its own.
Fonts - the quietest thing that breaks a file
Unembedded fonts are a silent project killer, because the preview on your computer looks perfect, and only after the file is opened on another workstation does the software substitute a replacement font and the whole text layout falls apart. PDF solves this problem, because it locks fonts inside the file, but only if you select the right embedding option at export.
A safer option for text that will no longer be edited is converting fonts to outlines before export. Then the text stops being text in the technical sense and becomes vector graphics - it no longer matters whether someone has that particular font installed, because its shape is already saved as an outline.
Layers, finishes and special elements
If a project has spot varnish, embossing, a die-cut or other finishing, these elements must sit on separate, clearly labeled layers, kept apart from the main graphics. The most common mistake in packaging files is exactly this - a missing, correctly prepared die-cut line, overlooked creases and gluing zones, and mixed-up layers for varnish or embossing - and all of this has to be fixed before the file goes into production, otherwise the machine simply will not know where to apply what.
It is similar with labels - the most common problem is an incorrect cut outline, missing safety zones and too little contrast in small typography, which becomes illegible faster on a small label than on a large format. If you are designing something smaller than a standard flyer, double-check that text near the edges has margin to spare, rather than reaching literally to the cut line.
Multi-page work - catalogs, brochures, books
For catalogs, the most common mistake is too small a safety margin near the spine, missing bleed and incorrectly prepared spreads - a graphic element stretched across the center of the book must account for the fact that part of the image will fall into the binding and may be partly hidden, especially with thicker print runs and glued binding.
In books there is one more level of difficulty - a miscalculated spine, meaning the thickness of the page block, incorrectly set cover pages, and too small an inner margin, which in a thicker publication with PUR glued binding can make text near the spine hard to read, because the page does not lie flat. With brochures, on the other hand, the biggest problems come from overlooking pagination and page order, and placing text too close to the cut line.
If you are designing something multi-page and are not sure how to calculate the spine or how to arrange pages in the correct order for folding, ask the printing house for a template or guidelines before starting work - that saves having to redo the entire document later.
Checklist - what to tick off right before sending
- File exported as PDF/X-1a or a correctly prepared composite PDF
- Gross format accounts for a 3 mm bleed on each side for catalogs, brochures, books, labels and packaging
- Safety margin of at least 3 mm from the cut line, and 5 mm or more for multi-page jobs
- All images at 300 dpi resolution at 1:1 scale (150 ppi acceptable only for large format viewed from a distance)
- CMYK color mode, not RGB, verified before export
- Fonts embedded in the file or converted to outlines
- Layers for die-cut, varnish or embossing kept separate from the main graphics and labeled
- For multi-page jobs, page order, pagination and spine margin checked
- File name clear and unambiguous, with no draft versions like final_final2
When it is still worth calling the printing house despite the checklist
Call when the project has an unusual shape, a non-standard die-cut, or combines several finishes at once, because in that case the checklist alone will not be enough - you need specific guidelines tailored to the particular technology and machine that will handle the job. A good printing house will respond to such an inquiry within 24 hours at most, so it is not wasted time, just a brief investment that can save the whole print run.
It is also worth asking in advance if you are not sure about the technology - offset or digital print, because that depends on a whole set of factors: format, volume, paper type, number of color versions, and whether you need personalization. There is no single magic quantity above which offset suddenly becomes more cost-effective - the advantage of offset grows with the print run and a stable production specification, and the printing house will help match the technology to your specific project instead of guessing.
The checklist we have gone through here will not replace experience gained from your own mistakes, but it eliminates most of the costliest ones - the wrong file format, missing bleed, too-low resolution, or mixed-up finishing layers. Five minutes of review before sending is really not much compared to a phone call from a client asking why their business cards have a name cut off.
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