Design Basics Part 1: Understanding CMYK and RGB

Part one of a new series: Explaining some of the “basic” concepts of design production. Having been asked to explain it recently, PikeMurdy will now attempt to shed a little light on CMYK and RGB color modes.

You’re a smart person. And you have to do a bit of an odd job, like say getting a home-made wedding invitation printed. Everything seems okay…but you don’t understand the difference between RGB and CMYK. First lets start with a bit of Color Theory:

All color visible to the human eye is formed from three basic “primary” colors: Red, Blue and Yellow. This means that, theoretically, any color you can see can be created by mixing Red, Blue and Yellow in certain values and in certain proportions to one another. This is really just a complicated way of saying: mix yellow and blue and you get green. Take all the colors away, you get white. Mix all the colors together in Exactly the same amount and at exactly the same saturation level, you get a shade of gray.

Of course, this is all theory and science. It is in fact, near impossible to get a perfect black by mixing red, blue and yellow.

Now a little bit of Colored light theory:

The primary colors of light are: Red, Green and Blue. Colored light behaves very differently than colored pigments, as a matter of fact, it behaves in many ways exactly the opposite of colored pigments. If you saturate the entire spectrum of light and intensify it, you get blinding white light. (if you saturate all colored pigments and intensify it, you get black). If you take all the light away, you get pitch black (if you take all the color away, you get white.)

Fortunately, unless you’re doing some freaky lighting on a photography shoot, or something crazy with optics for a science museum or something, you’ll probably never really need to understand how colored light behaves. Frankly, I don’t understand it.

All you need to know is, that there is a difference between colored light, and colored pigments and that they behave differently. Enough of theory, onto the real world:

When I referred to “Red” as being a primary color, I didn’t simply mean red. Primary red is extremely intense and extremely saturated. It hardly ever occurs in nature and it, being a basic building block of all colors, cannot be created by mixing any colors. Same goes for primary blue and primary yellow. And if you’re not working with the true primary colors, all bets are off. You cannot create every single color in the universe without the true primaries, and even then it’s difficult.

Enter CMYK. Sometime in the past century some enterprising printer came up with a system of four inks: Cyan, Magenta, Yellow and Black (Black is referred to as “K” so not to confuse it with blue). The inks are transparent. If you print a coat of cyan on top of a coat of yellow, you can see through the cyan into the yellow and it creates a “green” color. Wallah: Green, without having to print a green ink. If you complicate and multiply this concept, it becomes possible to print something, (such as a photograph that looks like it has thousands of different shades of color) but you’re actually using only four colors of ink: cyan, magenta, yellow and black. And printing four colors of ink is a lot cheaper than printing thousands of colors of ink.

That’s what CMYK (also called “process”, and sometimes called “four color”) printing is.

So what’s the RGB.

Computer monitors do not display colored pigments, they display colored light. Colored light behaves very differently than colored pigments. The primary colors of light are: Red, Green and Blue (RGB).

One thing that must be understood: you can’t print colored light. If you have an image that’s in RGB mode, you can send it to print on your printer, but the software in the printer automatically translates it to CMYK (and often not very well).

The monitor on the computer does the opposite. When you change an image to CMYK, the monitor must translate it to RGB to display it (which is why the colors on your print never quite match the colors on your monitor).

There’s no Red In CMYK.

Since CMYK is not based on the true primary colors, every color visible to the human eye is not possible. In fact, CMYK has a very limited range. A good, deep red is impossible. Blue is pretty hard too. Greens and Oranges are always dull. There are technologies out there that allow for six color process (adding an orange and a green color) but it’s yet to really have taken off.

RGB mode on your monitor is based on the true primary colors (of light), and therefore has a much wider range. You can choose hundreds of colors of varying values and degrees of saturation in RGB that will never be printable. (this is why when you switch from RGB to CMYK, you sometimes get a “dulling down” of colors).

So, CMYK is not perfect. In fact, printing really rich and vibrant colors with it is near impossible, but it is the most reasonably simple (and most popular) way of printing what seems to be a “full color” photo.