CMYK vs. RGB

CMYK vs. RGB for printing

Here’s a recap on the technicalities of Additive and subtractive colour reproduction…
or RGB and CMYK as you’ll probably know it.

 

RGB

RGB light from a prism

 

RGB stands for Red, Green and Blue.  It’s the colours which lie roughly at either extreme and the middle of the spectrum of light after it passes through a prism.  It’s sometimes called ‘additive’ colour, because the three added together actually form pure white light – imagine them passing back through the prism in reverse.

The important thing to realise is that RGB is how your monitor (or your TV or mobile phone) displays colour, though activation of red, green or blue pixels.  If the monitor is to display white, it will activate all three colours at that point.

Obviously one cannot print in RGB.  Inks added together or printed over each other, as every schoolchild knows, doesn’t result in white, so the whole concept of the display and the print would be incompatible.

 

CMYK

CMYK paint pots

 

That’s where Cyan, Magenta, Yellow and Key (black) come in.  Sometimes called ‘subtractive’ colour, cyan, magenta and yellow have been found to allow the closest approximation to RGB in print.  Supposedly, these colours added together should produce black, but it usually comes out as a muddy grey; a black is therefore added, called Key (to distinguish it from blue).

 

In Print

As printers use subtractive colours, your photos and graphics will have to be converted to CMYK at some point.  If nothing else, they will be converted during the printing stage as the file is processed by the printer itself.  For digital printing this is often fine and you can submit RGB files without worrying about the sky being green.  However, if you want to be sure of the changes you should convert the colours yourself.  This can and should be done using appropriate software, such as Photoshop, which uses various conversion algorithms suitable for different types of image.

For litho printing, your files MUST be in CMYK.  If you have no other options, at least save your file as a PDF using the PDF/X-1a profile, which converts the colours for you.  You can then check your file for undesirable changes.

Checklist:

  • Digital printing: RGB not a problem but colours will change
  • Litho printing: CMYK essential
  • Best to convert to CMYK yourself, to check colour changes

 

Lost in Translation

The ‘colour space’ refers to the gamut of colour which is reproducible by a given medium.  RGB, being closer to our visible light spectrum, provides the widest colour range (and even within RGB there are many versions); CMYK can reproduce far fewer colours, so some will be lost upon conversion.

CMYK vs RGB

 

This usually results in the colours looking ‘flatter’, less vibrant.  As technologies improve, these differences are becoming less of a problem, but until we have cheap, paper-thin, flexible page-screens, it’s just something we have to accept.  At FirstpointPrint, we have a printer which uses ‘vivid colour’ inks, which can help mitigate the problem.

Checklist:

  • CMYK colours are usually ‘flatter’
  • Many colours on your screen CANNOT be printed
  • Use CoatedFOGRA39 colour space

 

What about Pantone?

Pantone colours are a universal set of individual colours used for printing on litho presses.  The concept of RGB, CMYK and colour spaces isn’t really relevant to Pantone colours, as they’re basically a pot of paint used for consistent colour across a brand.  On a digital press, Pantone colours are converted to CMYK; in litho, the system will produce a separate plate for each Pantone colour on top of the CMYK plates, resulting in increased costs.  If that’s not your intention, convert all spots to process before submitting your artwork.  If you’re designing, say, a business card with two Pantone colours then that’s fine, just be aware of the colours being used in the design.

Again, it’s best to convert the colours yourself so you can see how they change.

Checklist:

  • Digital printing converts everything to CMYK
  • Litho creates a plate for each colour, including Pantones