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Knowledge Base - RGB vs CMYK vs PMS

Do you ever wonder why you can't just pick a colour on your monitor and have it come out the same in print? The reason behind this is quite complex - and it is a source of many issues that arise from interactions between customers, graphic designers and printers.

The key reason why there is so much difference in colour output between an image viewed on a computer monitor and a final printed product, is the fact that monitors and print have little in common as to how they produce colour.


RGB Colour Model
RGB Colour Model

RGB is referred to as the "additive colour model". It is used by devices that emit light.

RGB stands for the Red/Green/Blue. It is a colour model is used to produce images that you would typically see on a computer monitor, be it a classic CRT (cathode ray tube) or a modern LCD display. The RGB model allows for each of the 3 colours to carry a value between 0 and 255 (0 for completely off and 255 for completely on).

A typical carrier for the RGB signal is the traditional VGA cable that hooks up to most display equipment. Another common carrier is the component cable that is used on some television sets.

The RGB model uses a combination of 3 primary colours (red, green and blue) to produce the final required colour. In the RGB colour model the mixing of Green and Red produces Yellow - it will be quite obvious to anyone that dabbed in an art class that this would not quite work in print.

This subject can get complex, however the key point is that mixing light is quite a bit different to mixing paint.



CMYK Colour Model
CMYK Colour Model

CMYK is referred to as the "subtractive colour model". It is used by devices that do not emit light.

CMYK is the most common colour model that is used to produce what you would see in print. This colour model is used by most printing equipment - everything in range from large commercial digital presses to typical home laser printers.

There are 4 primary colours - Cyan, Magenta, Yellow and Black. The 4 colours are mixed to produce secondary mixtures.

The mixing process produces these outputs:

  • Cyan + Magenta = Blue
  • Cyan + Yellow = Green
  • Yellow + Magenta = Red

As you can see, CMYK is quite different to RGB:

  • There are 4 colours instead of 3
  • There is no light source - print jobs rely on an external light source
  • "White" colour isn't produced

How do you get a consistent CMYK colour?

The good news is that you can take steps to ensure your corporate brand looks consistent.

All professional graphic design software produces documents for print coded for the CMYK colour model.

Steps to colour reproduction in print:

  • Print out of a colour chart
  • Pick the colour that looks appropriate and note CMYK value
  • Have your graphic designer adjust the files with the selected colour

It is also very important for your printer to regularly calibrate digital printing equipment.

Can I convert RGB to CMYK?

The correct answer is No.

While there are tools that simulate RGB covers in CMYK, they are not accurate. The best course of action is to use a proper printed colour chart as noted above.

Does paper affect colour reproduction?

The same colour will vary across different paper stocks.

Pay specific attention as to what paper stocks match your company brand best.

Glossy, Matt and Uncoated stocks will all produce an image that varies slightly. Glossy stocks add shine and tend to be best at producing vibrant images and photographs.


Pantone Colour Matching System

PMS stands for "Pantone Colour Matching System". It is a proprietary system that has been developed to accurately match colours across different systems.

It is common to encounter PMS values when specifying corporate brand colours.

PMS extends beyond what a device operating under the CMYK model can produce - there are 1,114 spot colours in the PMS colour space that can't simulated by a typical digital press that operates under the CMYK colour model. Offset printing equipment can utilise PMS spot colours properly.

If your corporate brand specifies PMS colours, let your printer know in advance as the final result will likely end up quite different as to what you expect to receive.


written by Daniel Moisyeyev
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