Colour – CMYK & Spot, the differences explained

June 20, 2018

Introduction

Within the print industry there are a number of ways that colour is produced. If, however, you are designing a web site or email marketing campaign you do not have to worry about colour too much as every computer screen will be set to slightly different levels of brightness, contrast and colour so you have very little control. Within the world of print it is a different story and important that you know the differences and how they affect the final printed document.

RGB

The first way that colour is produced is the result of mixing 3 different colours of light and is referred to as RGB. These 3 colours are RED, GREEN and BLUE which are the 3 primary colours that when mixed together in different proportions produce different colours; this is how colour is created on your television screen and computer monitor. It is important to note that RGB has a high colour gamut which means that you can produce a large number of colours using this system and therefore images often appear bright and vivid. This is further enhanced by the fact that the colours are backlit via the computer screen making shadow areas appear lighter and detail higher. The majority of graphics packages will default to RGB in their colour settings.

CMYK

In print we use a mix of 4 inks – Cyan, Magenta, Yellow and Black to produce colour which is referred to as CMYK. Every image is split into small dots of these 4 colours and the varying size and density of the dots produces the different colours. When you view a printed image under a powerful magnifying glass or linen tester, you will see a pattern of these dots arranged  at different angles to form a rosette so that they do not print on top of each other – this is known as the screen angle. These dots are very small so when viewed by the human eye merge together to produce an image. The drawback of CMYK is that it has a smaller colour gamut than RGB and hence you can not produce as many colours which means images can look darker or flatter than RGB images on a computer screen. Shadow areas can also look darker and less detailed as the paper they are printed on is opaque and has no light shining through the back of it.

Both litho and digital printing use the CMYK system with the only difference being that digital print has a larger colour gamut than litho print so colours can look more vibrant and punchy. Where digital print falls down however is in the shadow areas that can often look dark when compared to the computer screen or litho printing. This is an issue that we often encounter as all modern digital equipment such a cameras and scanners are designed for images to be viewed via a computer screen. We would recommend lightening your images by 5% – 10 % if they are going to be used in digital printing.

Due to the colour gamut of CMYK, some colours are difficult or impossible to print. Perhaps the best example of this is with metallics and oranges, you simply can’t reproduce these colours using CMYK; you have to use spot colours.

Spot Colours

A Spot colour is a single colour ink that has been mixed beforehand using different ink pigments to achieve the required colour, similar to the tin of paint you buy from a DIY store. These clean, vibrant spot colours have been standardised across the print industry into a system designed by Pantone known as the Pantone Match System (PMS).

Whilst it is not possible to reproduce all of these spot colours out of the CMYK, pantone have produced a book called the Colour Bridge that shows you how accurately they can be matched and the exact CMYK breakdown required to achieve them. Before the advent of cheap, mass produced 4 colour print – spot colours were widely used.

Spot colours are often used by designers for company logos due to their cleanness and intensity. Care should be taken when choosing spot colours and consideration given to how they will be used. Spot colours can greatly enhance the look and impact of a printed job but they also add to cost and are only available for litho print.

Duo Tones

By mixing two spot colours either harmonising or contrasting can give striking vivid results which have more impact than standard CMYK. If producing black and white images you can add depth and warmth by using a grey to add detail and tone in the shadow areas. Back in the 80’s a lot of work was done using three splits – or Tri tone.

Tints

The last method used in colour reproduction is the use of tints. A tint or shade of a colour can add subtlety, depth and warmth to an image and is produced by breaking down the solid colour into a series of dots of varying size and density. You can do this for both CMYK and Spot Colours.