CMYK vs RGB: the beginner's guide to print ready colour for large format

RGB vs CMYK at a glance

RGB: colour made of light

Your phone, laptop, TV and camera all work in RGB. Every pixel is a tiny group of red, green and blue lights. Turn them all up to full and you get white. Turn them all off and you get black. Mix them at different strengths and you get millions of colours.

Because a screen shines light straight into your eyes, RGB can show colours that glow: neon greens, electric blues, hot pinks. That is why designs often look amazing on screen.

• RGB is called an additive colour system: more light means a lighter colour.
• It is the default for photos from your phone, images from the web, and most design apps, including Canva and PowerPoint.
• RGB values run from 0 to 255, so pure red is written R255 G0 B0, or #FF0000 in hex.

Pro tip Designing for social media and print at the same time? Keep two versions: RGB for screens, CMYK for anything going to print.

CMYK: colour made of ink

Printers do the opposite. They start with a white material, like vinyl, canvas or foamex, and lay down tiny dots of cyan, magenta, yellow and black ink. Each ink soaks up some of the light bouncing off the material. The more ink you add, the darker the colour gets.

• CMYK is a subtractive colour system: more ink means a darker colour.
• Values are percentages of each ink, from 0 to 100. A strong red is about C0 M100 Y100 K0.
• The K stands for key, which is black. In theory cyan, magenta and yellow together make black. In practice they make a dark, muddy brown, so printers add a real black ink for crisp text and deep shadows.

Our large format printers, the 3.2m Liyu roll to roll and the Fuji UV flatbed, print with CMYK based inks, the same as almost every commercial printer. So whatever you design, it ends up as CMYK on the material in the end. The only question is whether you see that change before it prints, or after.

Why some colours can't print: the colour gamut

The range of colours a device can show is called its gamut. Think of it like a box of crayons. Your eyes have the biggest box. A screen has a smaller box. Printing inks have a smaller box again, and it is a different shape, so some screen colours simply aren't in it.

When a colour sits outside the print gamut, it gets swapped for the nearest colour the inks can make. Bright greens, electric blues, vivid purples and neon brights are the usual suspects. Reds, oranges and yellows usually survive much better.

Pro tip If your design relies on a neon green or an electric blue, flag it when you send the file. We'll tell you how close we can get on your material before anything prints.

Real examples: screen colour vs printed colour

Here are pure screen colours next to the closest colour CMYK inks can print. The left half of each swatch is the screen colour, the right half is a typical printed result.

And here is how much of the brightness and punch each colour loses on the way to print. The bigger the bar, the bigger the change you will notice.

What that looks like on a design

Here is a bright event poster designed in RGB, next to a simulation of how the same file would print. Look at the neon green headline, the electric blue background and the mint circle.

On screen (RGB)Printed (CMYK)

Nothing went wrong with the print. The screen version was showing colours that ink simply can't make. Design in CMYK from the start and you would have seen the right hand version on your screen, and picked colours that still pop in print.

The full spectrum

The same thing happens across every colour. Top: a full spectrum on screen. Bottom: the same spectrum printed. Notice how the greens and blues flatten while the reds and yellows hold up.

On screen (RGB)

Printed (CMYK)

Getting black right

Black catches people out more than any other colour. A black that looks perfect on screen can print as a flat charcoal grey, especially across a big backdrop or hoarding.

• Use rich black (for example C40 M30 Y30 K100) for big black areas.
• Keep small text and thin lines in K100 only, so they print sharp with no colour fringes.
• Never use 100% of all four inks.

Brand colours and Pantone

If your logo has to be a particular shade, CMYK numbers alone won't guarantee it, because the same numbers look slightly different on vinyl, canvas or acrylic. Give us the Pantone reference or your brand guidelines and we will match it as closely as the material allows. We colour match all the time, from event branding to acrylic matched to Tiffany Blue.

How to switch to CMYK in your design software

Pro tip Your screen brightness changes how colours look. Turn it down to about half before judging colours, it gives a much more honest preview of print.

One golden rule: convert to CMYK before you fine tune your colours, not after. If you perfect a design in RGB and convert at the end, you will be disappointed by the change. Start in CMYK and every colour you pick is one that can print.

Large format extra: resolution

Colour is only half of a sharp print. The other half is resolution, measured in dots per inch (dpi). A small image stretched across a big banner turns soft and blocky.

Enough pixels

Stretched web image

For large format, aim for about 150 dpi at the finished size. Close up pieces like seating plans and canvas prints look best at 300 dpi. Here is how many pixels that means:

Don't panic about the big numbers at the bottom. Backdrops and hoardings are seen from metres away, so they usually print well at much lower resolution, and you can build them at 1:10 scale. Vector logos and text stay sharp at any size. If you are unsure, send the file and we'll tell you if it's sharp enough on your free file check.

Your print ready checklist

1. Set the document to CMYK before you start choosing colours.
2. Preview bright greens, blues and purples, and adjust anything that dulls.
3. Use rich black (C40 M30 Y30 K100) for big black areas, K100 for small text.
4. Note any Pantone or brand colours so we can match them.
5. Check images are about 150 dpi at the finished size (300 dpi for close up pieces).
6. Add 3 mm bleed and keep text 10 mm inside the edge.
7. Export a PDF, ideally PDF/X-4, and send it to us.

Want the full setup guide with bleed, safe areas, fonts and cut lines? Read our free artwork guide, or download it as a PDF.