What is the difference between RGB and CMYK?

No doubt you’ve heard of RGB and CMYK, but if you don’t understand what they are and what they’re used for, then read on! I will explain it for you as succinctly as possible.

Firstly, what do the acronyms stand for?

RGB = Red/Green/Blue
CMYK = Cyan/Magenta/Yellow/Black (Yes, K means Black!)

So what’s the difference between RGB and CMYK?

RGB and CMYK colours render differently, depending on which medium they are used for—web or print. Let me explain both:

colour space RBG

RGB

RGB colour mode is associated with electronic displays: LCD monitors, scanners, digital cameras etc.

It is an additive process.

It combines the three primary colours: red, green and blue, in varying degrees to create a whole range of colours.

When all three of the primary colours are combined and displayed to their highest value, the result is a pure white. When all three colours are combined at their lowest value, the result is black.

colour space CMYK

CMYK

Printers using a digital printing method print colour on paper using CMYK.

It is a subtractive process.

It utilises four colours: cyan, magenta, yellow and black in various amounts to create a range of colours for printing images and graphics.

It is a subtractive process. This means that as each additional colour is added, more light is removed and absorbed, resulting in new colour creations.

When the first three colours (cyan, magenta and yellow) are added together, it makes a dark brown. So, the K colour, or black, is used to completely remove light from the print, and allows the eye to perceive ‘pure black’.

CMYK does not include a ‘white’ colour, because when printed on white paper, the white from the paper will be used to fill the space left after the percentages of each colour that is used, and making each shade appear lighter.

How do I know when to use each one?

If you’re printing something, such as a business card or flyer, use CMYK.

If it’s something that will only be seen digitally, use RGB.
A digital monitor is made up of units called pixels. Then, each pixel is made up of three light units: one red, one green, and one blue. The RGB values are applied to the pixels, and so set the luminosity for each of the light units in each pixel.

Why? How do they render differently?

RGB has a greater spectrum of colours than CMYK, so it can produce colours that are more vivid and vibrant, such as fluorescent colours. The CMYK range is more limited.

The colours render differently based on (1.) the amount of white space that is already provided, and (2.) how much mixing of colours needs to happen.

To get the same colour ‘matching’ on all mediums, across web and print, the colours need to be converted. (An absolutely perfect match between the two types of colour modes is impossible, but when converted, a very close match is achievable.)

Going from RGB (web) to CMYK (print)

Because RGB colours are beyond the range of CMYK, they will appear darker and more dull in print than what is seen on the monitor or display.

Going from CMYK (print) to RGB (web)

Conversely, artwork shown in CMYK mode will always show up precisely on a computer screen, because its limited colour range easily fits into the full spectrum of the RGB range.

Example

Below is an example of a photo originally produced in RGB colors converted to CMYK colors as displayed on a computer monitor. Notice how the colors are much more vibrant on the RGB picture.

Conclusion

The artwork displayed on a computer monitor may not resemble its printed version unless you convert the colour mode properly first.

To accurately print a document or image, it must be converted from its original RGB format to CMYK. You can do this using Adobe Creative Cloud programs such as Photoshop or Illustrator.

The job of a graphic designer or pre-press professional is to check the effectiveness of colour conversions and offer advice on instances where more vibrant colours need to be converted from RGB to CMYK.

*Photo by Lucas Pezeta from Pexels

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