Ever set up something on the computer and loved the colours then gone to print it and it looks horrible, dark and muddy?
This is because your screen is made up of many clusters of three little lights called LEDs (which stands for Light Emitting Diodes for those that are curious) in the colours of Red (R), Green (G), and Blue (B). Your eye tricks you in blending those three lights together to make a solid colour and depending on how BRIGHTLY lit those lights are will vary the colour produced. For example if only the Red light is on at 100% light and the Green and Blue were turned off completely at 0% light then you would see the colour Red.
And because of this RGB is known as an additive colour mode. It is called additive because the background of a screen starts off black and then the individual LEDs light up in varying intensity adding light to black.
CMYK (Cyan Magenta Yellow and Black), which is used for printing, on the other hand is known as a subtractive colour mode because the paper starts out white and the ink subtracts from the brightness of the white paper.
If you ever get the opportunity to look VERY closely at a printed picture you will see that it is made up of many tiny little dots of CMYK (unless printed in other formats which I will not go into here like spot or Pantone colouring) and they are printed very close together or far apart to once again trick the eye that you are seeing a colour. Rather than reproducing black by combining the three colours, CMYK uses an additional colour to RGB which is “Black”. Imagine trying to put three little dots on top of each other EXACTLY just to form part of a letter or even a straight line.
So back to the original point about looking at something so BRIGHT on your monitor and then printing it out to see it’s rather dark or BLACK on paper. Here is an example of how this might work.RGB actually has many more colour variations available than CMYK. When a file in RGB tries to print in CMYK it pushes the colours out of the range of the CMYK’s capacity and hence you get that “muddy” or “dirty look. However a CMYK file being converted to RGB is fine as the RGB palette can accommodate the CMYK variations.
A great designer should always work files in CMYK in the beginning and then only convert files to RGB if needed for screen products (like websites, powerpoint presentations etc) that way you always have images ready to go for print!
Have you experienced the outcome of printing a brightly coloured RGB file on the printer only to be disappointed at the dull quality? I would love to hear about it.