Within the print industry a distinction is made between different colour systems, between RGB, CMYK and spot colours. Below we explain the differences and applications.
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 is the system we use for emitted light. Every RGB colour is made up of varying proportions of the 3 primary colours: Red, Green and Blue. This is how colour is created on your television, computer screen or phone. It is important to note that modern RGB screens have a much higher colour gamut (range of possible colours) than is available for CMYK printing. Many of the colours available on a computer screen, particularly those that are vivid or flourescent, are just not reproducable with CMYK printing methods. The majority of graphics packages will default to RGB in their colour settings.
For CMYK colour printing we use Cyan, Magenta, Yellow and Black inks to produce a colour image. Every image is separated into these 4 colours, and broken down into small dots of varying size and density which when combined on the printed surface produce the different colours. If you view a printed image under a powerful magnifying glass you will see the pattern of these dots arranged at different angles to form a rosette, so that they do not overlap and so 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 cannot 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.
A Spot colour is a single colour ink that has been mixed before hand using different ink pigments to achieve the required colour, similar to the way a tin of paint you buy from a DIY store is mixed. 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).
It is not possible to reproduce all of these spot colours from CMYK however Pantone have produced a book called the Colour Bridge that shows you how closely 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.
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 Tritone.