CMYK vs. RGB: A Beginner's Guide

What are RGB and CMYK?

CMYK and RGB are two systems for mixing colours.

Computer monitors emit colour as red, green and blue light. We call this RGB.
Printers print in cyan, magenta, yellow and black inks. We call this CMYK.

When you print anything, the software you use takes the colour information stored in your file in RGB format and sends it to the printer, which works out how to remake those colours by mixing CMYK inks together. This allows the printer to recreate the colours you see emitted as light from your monitor. It can't mix as many colours from CMYK as your computer can from RGB light, so the colours look quite a bit different in print to how they do on your screen.

If that's hard to wrap your head around, here's an analogy: your computer speaks one language, and your printer speaks another. They don't have all the same words in their languages so sometimes they have to use something that sounds similar, but isn't quite the same, when they translate from one language into the other.

The printer is able to automatically convert the colours itself, but because it doesn't have access to the original information, it doesn't always make a very good job of it! This means that if you want to have more control over your colours, you need to get your computer to convert the colours to CMYK either before or when you export your file as a PDF.

How does the printer make all those colours from just four inks?

A traditional newspaper press has four metal plates, one for each of these colours. During the printing process the paper rolls over these plates and the ink is transferred to the page in varying amounts. These amounts are defined in percentages in your software. For example, a dark blue might be made up of 100% cyan and 100% magenta, also written as C100 M100 Y0 K0. Digital printing does not use plates, although it still uses CMYK.

When you upload a file to our website, our system will scan it and let you know if there are RGB colours there. If you don’t know how to convert these to CMYK – don’t worry. When you place your order we will print it if we can, and if we can't we will get in touch to try and help you work out how to convert the colours if you haven't managed to.

If you have any questions about working with colour please get in touch at support@newspaperclub.com