Working with printed colour requires not only creative flair, but also some technical knowledge about how colour is produced in print. In this article GSM takes a look at getting the most from CMYK colour.
In the world of offset print, CMYK stands for Cyan, Magenta, Yellow and Key (black). It is also known as process colour. What is important to understand with offset print is the difference between onscreen colour and printed colour.
There is nothing worse than seeing that the colours of a freshly printed piece don’t look anything like they did on-screen. This is not the fault of the printer but the result of not having a sound understanding of how colour works in print…
RGB versus CMYK
Firstly, let’s look at the basic differences between RGB and CMYK.
Digital devices use the RGB colour model. Red, green and blue light is combined to create colour. Combining all three light colours at their strongest intensity creates white, black is achieved when all the light is dimmed to zero output (i.e. the lights are off).
In comparison, printing using the CMYK colour model involves four transparent inks: cyan, magenta, yellow and black. These inks are laid down over each other in a dot screen pattern onto paper. A combination of the differences in the overlaying screens and the amount of light reflecting off the printed surface creates the colours we see. When you don’t print any ink, you get white—the white of the paper.
These differences between the RGB and CMYK colour models mean that they do not share the same range of achievable colours.
RGB uses generated light to make colour, rather than relying on reflected light like CMYK. This means that RGB is able to depict significantly brighter and more vibrant colours than what CMYK printing is able to replicate. This is particularly evident if you look at oranges, violets and turquoise colours printed in CMYK. These colours tend to lack intensity when compared to their RGB counterparts.
Put simply, RGB and CMYK colour cannot appear the same because they employ completely different fundamental principles.
Going from Screen to Print
So, how can you know for certain what the colour on your computer screen will look like in print?
Recently, the team at BJ Ball produced a range of six CMYK wall colour charts—called CMYK MIX. Charts like these were common until around a decade ago, often produced and supplied by your local commercial printer. In recent years they have become scarce— so BJ Ball have produced their own version.
These colour charts are a powerful tool for the professional graphic designer. Each chart takes one of the base CMY colours and shows how the colour changes with the addition of another one, two or three process colours. There is no K (black) wall colour chart, as combinations using black are shown on the other three C, M and Y charts.
Experienced print designers will tell you to always work in CMYK mode for print. Do not create artwork in RGB mode and convert it to CMYK at the last minute. Or worse, send RGB mode artwork to print. If you are working in CMYK mode, you will have colours in your Swatches list in Illustrator or InDesign that use the CMYK colour formula (figure 1).
To know how a particular colour is going to print, look at the CMYK formula in Illustrator or InDesign, then find the closest match on one of the wall colour charts (figure 2).
For practical purposes, the wall colour charts use increments of 10%. This may not exactly match the colour you have in your
digital swatch but it will be perceptually close. Sometimes you will see surprising results. For example, a vibrant on-screen orange when compared to the printed equivalent on the wall colour chart appears dull and flat. The key here is to not trust what you see on-screen. Rely on the wall colour chart as it is closer to how a colour will actually print.
Colour on Paper
Another factor that may affect how the colour looks when printed is the paper stock itself. Due to the difference in light absorbency of the paper’s surface colours print differently. Colours printed on a coated stock will usually appear brighter than they do on an uncoated stock. For this reason, BJ Ball has produced these wall colour charts on both coated and uncoated paper stocks. In this way you will get a more accurate idea of how the colour will look when printed.
Obviously, a coloured or off-white paper stock will yield a different result again. In this situation, we recommend you
contact your BJ Ball paper consultant. They will provide you with a printed sample so you can gauge the resulting colour.
To Sum Up
- Always work in CMYK colour mode in Illustrator, InDesign and Photoshop to get the most from printed colour..
- Refer to a CMYK colour chart to see how critical colours are likely to reproduce— don’t trust what you see on-screen!
This article was originally published in GSM11. To read this and other great articles purchase this issue here.