The design looked superb on the monitor. It arrived from the printer looking muddy, slightly cropped, with a headline that fell off the edge and a background that ended two millimetres short of the paper. Nothing went wrong at the press. The file simply described a different medium from the one it was printed on.
Screens emit light and paper reflects it. Almost every surprise in print follows from that one sentence.
Resolution: the number that is not a property of the file
An image has a pixel count. That is all it has. The dots per inch figure is a note attached to the file saying how large those pixels should be printed, and changing it without resampling changes nothing about the image at all.
The arithmetic is what matters. Physical size times the target density gives you the pixels you need. A photograph printed at 10 by 15 centimetres, which is roughly 4 by 6 inches, at 300 dots per inch, needs 1200 by 1800 pixels. An A4 page at 300 needs about 2480 by 3508.
Three thresholds worth memorising:
- 300 dpi for anything held in the hand. This is where individual dots stop being resolvable at normal reading distance.
- 150 dpi for posters and anything viewed from a metre or more. Viewing distance is the variable everyone forgets: a billboard is often produced at 20 dpi and looks perfect from the road.
- 72 dpi means nothing. It is a historical figure for old monitors and appears in print conversations only as a source of confusion.
Enlarging a small image to meet a dpi figure does not add detail. It adds interpolated pixels, which print as softness. If the pixels are not there, the honest options are to print smaller, use a different image, or accept the softness deliberately.
Color: why the printed version looks flatter
A screen makes color by adding light: red, green and blue emitters, and all three at full strength gives white. Paper makes color by subtracting: cyan, magenta and yellow inks each absorb part of the spectrum, and all three together gives a muddy brown, which is why black ink is added as a fourth.
These two methods can produce different sets of colors, and the printed set is smaller. Saturated blues, vivid oranges, bright greens and anything neon can be displayed and cannot be printed. The press does not fail: it substitutes the nearest color it can mix, which is duller, and every neighbouring color shifts slightly to keep the relationships.
The practical consequences:
- Do not judge saturated color on a screen. Use a soft proof, which simulates the printed result using a profile for the specific paper and press.
- Convert deliberately, not accidentally. Design in the color space you were given, and convert once, at the end, with the right profile, rather than letting three pieces of software each guess.
- Beware of rich black. Black text should be pure black ink only. Black built from all four inks is for large solid areas, and using it for small text produces registration fringing when the press is a hair out of alignment.
- Paper is not white. Uncoated stock is warm and absorbs ink, so everything prints slightly darker and softer. Coated stock holds detail and looks more like the screen.
Bleed, trim and the safe area
This is the one that causes reprints, and it is pure mechanics.
Pages are printed on oversized sheets and cut down in a stack. The blade is accurate to a fraction of a millimetre, and the stack shifts. So the cut lands somewhere close to the intended line, not exactly on it.
Three zones follow:
Bleed is the area beyond the finished edge, usually 3 millimetres. Any color or image meant to run to the edge must extend into it. If it stops exactly at the trim line, a slight misalignment leaves a white sliver, and a white sliver along one edge is instantly recognisable as a mistake.
Trim is the intended cut line, the actual finished size.
Safe area is an inset from the trim, usually 3 to 5 millimetres, inside which all text and anything else that must not be clipped should sit. Text placed 1 millimetre from the trim edge will occasionally be cut into, and will always look uncomfortable.
Design at the trim size, extend backgrounds into the bleed, keep content inside the safe area. Every printer’s specification says this and every printer receives files that ignore it.
The details that ruin an otherwise correct file
Hairlines. A line defined as zero width or 0.1 point may render on screen and disappear or break up on paper. Keep rules at 0.25 point or thicker.
Transparency and effects. Drop shadows, glows and blend modes have to be flattened for print, and flattening can shift color or produce visible seams. Check the flattened output rather than the live file.
Fonts. Embed them or convert text to outlines. A missing font substituted at the press changes the line breaks, and nobody notices until it is printed.
Small reversed text. White text on a dark background, below about 8 point, tends to fill in as ink spreads slightly into the paper. Reversed text needs to be larger and heavier than the same text in black.
Ink coverage. Large areas built from heavy amounts of all four inks may exceed what the paper can absorb, causing set-off and long drying times. Most presses want total coverage under about 300 per cent.
When paper does something screens cannot
It is worth remembering why anyone still prints. Paper has a physical size that does not change, it works without power, it can be folded, cut, stuck to a wall and handed to somebody. A calendar on the kitchen wall is glanced at fifty times a day, which no notification achieves.
That opens a category of work that only exists on paper: things that get folded, punched, threaded or assembled. Those carry an extra geometry on top of everything above, because a fold line in the wrong place is not a visual error, it is a thing that will not close.
Before you send the file
- Correct physical size, with bleed added on every edge.
- Every image at sufficient resolution for its final printed size and viewing distance.
- Converted once to the right color profile for the paper and press.
- Black text in black ink only.
- Fonts embedded or outlined.
- Nothing important inside the safe margin.
- Soft proofed, and looked at, rather than assumed.
Seven checks, five minutes, and it is the difference between a proof and a reprint.
