If you want your colours to print in a specific way, then it helps to have a basic understanding of how colours & printers come together. In this article, we’ll explain how colours print, and what you need to consider when preparing your files for print.
- Card Sizes: things to consider
- Image Resolution
- Understanding Colour modes (CMYK vs RGB vs Pantone) – you are here
- Bleed and Trim
- Finishing Layers (Foil, flitter, emboss)
- Getting Files Press Ready Checklist
- Working with your Printer
The Colour Gamut
Think of all the colours that are available to the human eye. Your computer screen, tv, phone, tablet etc can only show you a subset of all those colours. Printers too can only print a subset of all those colours. The range of colours is called the colour gamut.
Screens use a system called RGB. Printing uses a system called CMYK. These are explained in more detail below, but the the important point to note is that the colour gamut for screens and the colour gamut for print are slightly different. They don’t overlap exactly, as illustrated in the image below:
What this means is that the colours you look at on screen will not always convert exactly to the same colour in print. Let’s look at the colour systems individually.
RGB stands for Red, Green Blue. It’s the system used by screens to display colours. All colours you see are made up of a combination of these 3 primary colours. RGB is an additive colour system – if you add all the primary colours together you get white. Take them all away, and you’re plunged into the darkness called black.
CMYK is the most common colour system used for printing. You’ll sometimes hear it being called the “four colour process”, or “process colour”. CMYK stands for Cyan, Magenta, Yellow and Key (black). They refer to the four plates that are used in the four colour printing process. If you have an inkjet printer at home or in the office, you’ll be familiar with these colours when you replace the ink cartridges. Commercial printers use the same colour process, just on a much bigger scale. Each colour is applied by way of a “plate”.
Just as all the colours in the RGB colour gamut are created by combining the 3 primary colours, the colours in the CMYK gamut are created by combining four colours on the printing press. However CMYK is a subtractive system – you get white by removing all four colours (areas of white board that your don’t print on remain white). Black comes from combining all the colours together.
Why do we need the black in CMYK?
You may be asking why there’s a need for a separate Black plate if C+M+Y gives you black anyway? Good question! The Black plate is there to bring together the theory and practice. In theory, adding C+M+Y should give you black. In practice, due to the nature of inks, absorptions of boards and other factors, it ends up being a murky dark brown. So a fourth black colour is introduced to get to a proper black print.
Pantone – Spot Colours
It is possible to print specific colours instead of making them up with a combination of CMYK colours. This is called using Spot Colours. (You can even combine the four colour process with an extra spot colour if needed – that would be an extra plate and or an extra pass along the printer so would probably add to the cost).
When using Spot Colours, you’ll probably use the Pantone Matching System (PMS) of colours. Pantone is a proprietary system of colours that was first designed in 1963. There are over 1800 standardised colours on the Pantone system, and each one has a unique code. Some can be reproduced with CMYK, but many are completely unique. Pantone also includes speciality colours like metallic and fluorescent colours.
Choosing between CMYK and Pantone
There are many factors to take into account when deciding whether to use CMYK, Pantone or a mixture of the two. You shouldn’t make the decision in isolation – speak to your printers too, to see what advice they can offer and what their capabilities are. Here are some of the factors to consider:
How important is colour accuracy?
With CMYK, colours can vary slightly between print runs – there’s a tolerance of what’s acceptable. With Pantone colours, the colour reproduction will be more accurate, since they are set by specific standards. However, keep in mind that even with spot colours, there can still be variations across print runs.
How many colours?
With CMYK, you can print a wide variety of colours covering the majority of the spectrum. With spot colours you are limited to the number of plates your printer can offer (typically 5 or 6). Spot colours tend to add extra cost and complexity to designs, but can also achieve a striking finish. Some card designers have used spot colours in the recent neon trend to make a particular element of a design stand out.
Do you need speciality colours?
If you need speciality colours like fluorescent or metallic colours, they you will need to use a spot colour solution.
The type of printing you choose can have a significant impact on the cost of your print run. Discuss with your printers early in the design stages, to avoid surprises later on!
What to consider when supplying files to your printer
The first rule is simple – ask your Print Supplier. Each Printer works in their own way and so it’s best to be sure what of what their requirements are before preparing a full range.
If you’re using a Litho printer then you will probably be asked to supply your files in CMYK. Otherwise your Printer will need to convert your file to CMYK and this can (and probably will) result in a colour shift – probably not what you want. It’s best to create the files in CMYK and have full control over what colours you are submitting for print.
Having said that, some Printers (like some of our Digital Print suppliers) will do the conversion from RGB to CMYK for you and they may have tools and software to get a higher colour fidelity than you can on your own (because they can match the profile of their own print machines). This is why the first rule is so important! Engage with your printer early, and save time in the long run.
If you’re using a combination of CMYK and spot colours then your printer will probably want the spot colour in it’s own layer – again, speak to your printer about how they want files supplied.
You can see how the colours will separate into plates using the Adobe Acrobat Print Preview Tool (You’ll need Adobe Acrobat Pro for this).