The blue on your screen is not going on the press

Two different physics

A screen makes colour by emitting red, green and blue light. Add all three and you get white. A press makes colour by putting cyan, magenta, yellow and black ink on paper that absorbs some light and reflects the rest. Add all four and you get a muddy dark brown, which is why black is printed separately.

These produce different ranges of reproducible colour, and the screen’s is larger in the areas people care about most: saturated blues, vivid greens, bright oranges, anything neon.

So some colours you can see on a monitor cannot be printed. Not “printed slightly differently”: cannot be printed. The press substitutes the nearest available colour, and a vivid cyan-blue arrives as a duller, greyer blue.

What actually happens

A generated image is in sRGB. Converting it to CMYK for print maps every out-of-range colour to the nearest reachable one. The typical result:

• Saturated blues lose vibrancy and shift toward purple or grey.
• Bright greens dull noticeably.
• Vivid oranges and reds lose their glow.
• Deep blacks become lighter unless a rich black is specified.
• Subtle gradients can band.

If the image was graded to look good on a screen, this conversion can be a shock.

Soft proofing, free

You can see it before printing. GIMP has soft-proofing built in: View > Color Management > Soft-Proofing Profile, pick a CMYK profile, and enable the gamut warning, which marks unprintable colours in a flat grey.

Two decisions follow from what you see:

If little is flagged, proceed. Convert at export and it will be fine.

If a large area is flagged (a sky, a background, the brand colour) fix it now. Reduce saturation in that range, or re-grade the image toward colours the process can reach. Doing this yourself gives a controlled result; letting the converter do it gives whatever the algorithm decides.

Scribus does the same and is the better tool if the image is going into a layout anyway.

Practical rules

Work in RGB, convert at the end. RGB is a larger space and you keep more information through the editing. One conversion, at export.

Ask which profile. Different presses and papers use different profiles: coated and uncoated stock differ substantially. The printer will tell you, and using theirs beats guessing.

Black is not black. 100% K alone prints as a washed dark grey on large areas. A rich black (around 60C 40M 40Y 100K, though printers vary) is what you want for large solid blacks. Ask.

Colour on uncoated paper is duller. The ink sinks in. Everything is softer and lighter than on coated stock, and this surprises people more than the gamut conversion does.

Screen has its own version of this

Not a gamut problem but a consistency one. Your monitor is not calibrated, the client’s is different, and phones apply their own processing. An image graded on a warm, bright laptop will look cold and dark on somebody else’s cheap external display.

Two mitigations that cost nothing. Check on a second device, ideally a phone, before sending. And avoid grading to the edges: an image that depends on the last 5% of shadow detail will lose it somewhere.

If you have a colorimeter, calibrate; if not, at least set the display to a neutral factory profile rather than a vivid picture mode.

The position

The vector-and-print course in this catalogue covers preparation for press properly: bleed, marks, overprint, profiles, preflight. What matters here is timing: the colour conversion is a decision made while the image can still be changed, not a checkbox at export.

And a limitation worth stating plainly: there is no way to make a printed image match a screen exactly, because the two are physically different media. The goal is a printed result you have seen, approved and are not surprised by. A client who says the printed poster looks duller than the screen is describing physics, and the conversation goes very differently depending on whether you showed them a soft proof beforehand.