Have you ever wondered why the colour of your printed photos is never quite the same as they were on your phone or computer screen? Have you been disappointed with a brochure or flyer you’ve printed because the colours weren’t as vibrant as they appeared onscreen? The main reason for this is the difference between the RGB and CMYK colour models. In this post I’ll expand on the two colour models and what they’re used for.
CMYK and RGB colours appear differently in digital and print applications
If you’re working on a design it’s important to know the difference between the RGB and CMYK models, as there is a lot of confusion about them.
There are two basic categories for colour types: print and onscreen. It’s important to understand that digital and print mediums render colour very differently from one another and choosing the correct one is crucial to the appearance of your final artwork.
What is RGB colour?
RGB is the most common colour model as it used in electronic devices like computers, TV screens, and smartphones.
RGB is an additive model that combines the primary colours of red, green and blue light to create a wide spectrum of colours – 16,777,216 to be exact. TechTerms explains more on how this calculated.
Pure white light is produced when all three primary RGB colours are combined at their fullest intensity.
At their lowest intensity, there is no light and the human eye interprets it as black.
Photo editing software programs like Adobe Photoshop use the RGB model by default as it offers the widest range of colours.
What is CMYK colour?
CMYK is used in commercial offset and desktop colour printers. It is created through a combination of the colours, cyan (C), magenta (M), yellow (Y) and black (K).
You may be wondering why K is used for the black plate and not a B. The reason for this is because in CMYK printing, K stands for “key” as black is usually used as the key plate and printed first. The other colours are aligned to the key for printing.
This what a CMYK image looks like when viewed through a magnifying glass.
Image by Zewan / CC BY-SA
CMYK is a subtractive process meaning that all colours start as blank – the white of an unprinted page. CMYK inks are printed in consecutive layers to create the the colour range.
Which colour model do I use?
Use the RGB colour model if your artwork is to be displayed on any kind of screen. This includes anything that involves computer screens, smartphones, tablets etc.
If you are printing, use the CMYK model as RGB colours will appear differently when printed to what was displayed onscreen.
When to use RGB
Work intended for display on digital screens will benefit if the RGB colour model is used.
Computer and other screens use the RGB model exclusively because digital monitors are made up of tiny units called pixels. Pixels are made up of tiny light units, one for each of the three colours red, green and blue. The colour range is created when the RGB values are applied to the individual pixels by setting the luminosity of the light units for each pixel.
Due to the wider gamut or range of colour available in RGB, colours will always be brighter and more vibrant than those produced with CMYK.
RGB is best for
Web and app design
- Online logos
- Online advertisements
- Images for posts
- Profile pictures
When to use CMYK Colour
The four colour CMYK process is the best method to use for anything that will be printed. Rather use RGB for anything that will be viewed onscreen.
Because of the wide range of colours available with the RGB model, there are colours that are outside of the range possible with CMYK printing. These colours may include special corporate or branding colours, metallic and fluorescent colours. It will only be possible to print these colours using spot colours. See my post on CMYK and Spot Colour Printing for more information.
CMYK is best for
- Vehicle Wraps
- Header cards
- Backing boards
- Boxes and cartons
Converting RGB to CMYK
As they are created differently, it is impossible to accurately convert RGB to CMYK without losing some colour. Due to the subtractive process used in CMYK, colours will never have the same brightness and vibrancy of RGB.
Commercial printers are able to covert RGB to CMYK, but many still prefer that you covert colours yourself before sending them artwork for printing.
Converting colours before for printing will allow you to make adjustments where necessary rather than leaving it to chance with an automatic conversion. Read more in my post on Preparing Artwork for Print.
Wrapping up the differences between RGB and CMYK
If the final output is for a screen, use RGB. If the output is printing, CMYK is the best option. It is important to remember that different devices and printers render colours differently from what you may see on your screen.