CMYK vs RGB Colour – Tony’s Tech Tips

by Tony Gamble

Tony's Tech Tips LogoToday’s tech tip clears up some colour confusion for a reader who wrote in “What’s the difference between RGB and CMYK?”. This comes up when working with images and graphic designs, especially when you’d like to have something printed professionally for your next project.

RGB coloursRGB refers to a colour model in which a single colour is produced by adding variants of red, green and blue together. This makes it an additive colour model, and in the realm of electronics, has been employed since the first colour televisions. Based on a colour theory called trichromatic colour vision developed in the mid-1800’s, RGB is the standard display method for computer monitors, phones and TVs. The colours on this website are built with six-digit codes that tell the browser what level of intensity to display each of those three primary colours. For example, the banner at the top is represented by the hexadecimal code #ad1465, which means Red is set to about 68%, Green at about 8% and Blue at 40% (the letters are the result of the hexadecimal numbering system that goes from 0 thru 9, and then A thru F).

So if everything looks so lovely in RGB, why then do we have this other colour model called CMYK? The reason is the medium. Turn off your screen. Go ahead, I’ll wait.

CMYK coloursPretty dark, wasn’t it? As I mentioned before, the RGB method that your screen uses is additive. It starts with nothing and adds the three primary colours together to achieve the desired result. Typically, when we print a hard copy, it’s printing on white paper. This is where the subtractive colour model of CMYK comes in. This method uses variants of Cyan, Magenta, Yellow and Black. Wait, wouldn’t that be CMYB? Well, since B is more commonly used to refer to the primary colour Blue, the K actually refers to Black in this case, or more specifically to Key black. Ink doesn’t behave in the same way the materials on your screen do, so Black is used as a key to manage the blend of the CMY colours. In fact, when you convert a RGB image to CMYK, you’ll notice that it may not look quite right on your screen, but it is a necessary step for the best results when printing with ink. This is why, when you submit a design to a site like Vistaprint or Cafepress, they’ll usually ask for your design in the CMYK colour mode.

Have any other technobabble terms puzzled or confused you lately? Let me know, and I’ll see if I can clear things up. Find me on Twitter @trinzitter, or leave a comment in our Livefyre box below.

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