In this blog we are going to cover the various colour models, why they exist, their limitations, and how we move from 1 model to another.
What is colour?
Before we can understand the different colour models, It’s a good idea to understand what colour actually is.
Colour can be defined as a psychological and physiological phenomenon created by an object, an observer (you or me), context, and light.
The illustration below helps to show what this means.
What this really means is there are many different factors that can affect the colour you or I see. These include:
- The colour or temperature of the light (the colour of light sources are often measured in kelvin with daylight being roughly 5000-6500k and the orangey light from spot lights being roughly 2700k.)
- The colours of other objects in the surrounding area. This includes the different colours of the object itself.
- Our physiology, this is especially noticeable when considering people suffering from colorblindness. This is usually caused by an inherited problem or variation in the functionality of one or more of the three classes of cone cells in the retina.
Did you know that children of people who suffer from colour blindness can sometimes have a 4th cone in their retina. This makes it able to see colours that others would not be, typically in the yellow-greens. - Our upbring. Thats right, even where we grow up and affect how we perceive colour, but when you think about it, it makes total evolutionary sense. People growing up in very green (forest) environments need to be much better at picking out different shades of green and brown. Compare this to people who grow in arctic environments. They need to be able to see many more different shades of white.
What this all means is that an object can appear different colours to different people.
RGB vs CMYK
RGB is based on the visible light spectrum, but even so it does not fully encompass the entire spectrum of colour that we can see with the human eye.
In the back of our eyes, we have a retina, which contains around 6 million cones. These cones come in 3 different varieties designed to see different wavelengths of light.
These are the wavelengths of the 3 different primary colours, Red, Blue and Green.
With this colour model, the more of all 3 colours the closer to white you get. This is called an additive colour model, as the colour you see is a combination of the 3 primary colours.
CMYK or Cyan, Magenta, Yellow, and Key (or Black) is a subtractive colour model. In this colour model, each colour acts as a filter, subtracting varying degrees of red, green, and blue from the white light.
As you can imagine from these descriptions, printing in RGB would be impossible. There is no way we could mix red, green and blue inks to create a white. We have to start with a white surface by using white vinyl or paper. Alternatively, we can create a white surface by printing onto the clear or coloured surface with white inks.
Therefore, printers use the CMYK colour model. This refers to the 4 colours of ink used in the printing press.
CMYK has a much more restrictive colour gamut or range compared to RGB. Consequently, many colours that you can see and create on a design program, cannot be printed accurately. To give you an idea of the difference in colour range, there are roughly 16,000 different colours available through CMYK, but over 16,000,000 are available using RGB.
Some newer digital printing presses that have the additional colours Orange, Violet, and Green that do extend the gamut, but still cannot match that of RGB.
If you print an RGB design, any colour that sits outside the CMYK colour gamut will have to be changed by the printing system to the closest colour inside the gamut. This can result in your final print not looking as you expected it to. Oranges, Greens and blues are particularly limited as CMYK colours vs their RGB counterparts.
How to convert RGB to CMYK
So how do you convert your artwork from RGB to CMYK?
The easiest is to use CMYK from the start, but it is possible to switch existing artwork to CMYK.
Photoshop
In Photoshop you can start a new document and switch the colour mode to CMYK, by going File > New > Color Mode > CMYK Colour
Alternatively, you can change your existing artwork by going Image> Mode > CMYK Color. Simple.
Illustrator
In Illustrator you can start a new document and switch the colour mode to CMYK, by going File > Document > Color Mode > CMYK Colour
Alternatively, you can change your existing artwork by going File > Document Color Mode > CMYK Colour. Simple.
Other colour systems
There are many other colour systems and models that exist, such as LAB or HSL, but the ones that we get asked about frequently are HEX, RAL, and PANTONE.
HEX
HEX or hexadecimal colour or codes are RGB colours, but they are expressed in a way that is understood by a 8-bit system. These are mainly used in CSS for web design and other computer or mobile applications.
Each channel is RGB is described as an integer that is made up using a combination of the digits 0 to 9 and the letters a to f.
Colour matching systems
RAL and PANTONE are both colour-matching systems. They both create various ranges of spot colours. These colours are often created using a range of 11+ base colours. These colour matching systems are great for brands trying to ensure all their products and materials match. The problem is, trying to recreate lots of these colours using CMYK inks, is very difficult/impossible.
RAL
RAL was created in 1927 in Germany and is used mainly for varnish, power coating and plastic colourings, and is made up of 2530 different colours.
Pantone
Pantone was created in the 1950s in the US and is widely used by graphic and fashion designers.
Pantone uses 11 base pigments to create their colours. As such it is very hard to reproduce most of these colours when printing using digital CMYK printers. Printers that contain OVG (Orange, Violet, and Green) inks in addition to the standard CMYK are capable of reaching many more of the Pantone colour range, but can still only hit around 90%.
Colour matching systems often create colour bridge books such as this one from Pantone. These show designers both the original Pantone colour as well as the CMYK colour they consider the closest possible. As you can see, some colours are very close, but others can be very different.