Defining the CMYK 4-Color Process Printing

CMYK inks combine to make thousands of colors

Magenta, cyan, yellow and black ink wells
pbombaert / Getty Images

When you view a full-color photo on your computer screen or digital camera, you are seeing it in a color space called RGB. The monitor is using combinations of red, green and blue—the additive primary colors—to produce all the colors you see.

To reproduce those full-color photographic images on paper, printing presses use four colors of ink that are designated as process colors. The four process inks are applied on paper or other substrates in layers of dots that combine to create the illusion of many more colors. CMYK refers to the names of the four ink colors used on the printing press—the subtractive primaries plus black. They are:

  • C is cyan (a blue color) ink
  • M is magenta (a reddish-pink color) ink
  • Y is yellow ink
  • K is pure black ink

A separate printing plate is made for each of the four process colors. 

Advantages of CMYK Printing

The costs of printing are directly related to the number of inks used in a printing project. Using CMYK process inks to produce full-color images limits the number of ​inks in a project to only four. Almost every full-color printed piece—whether it is a book, menu, flyer or business card—is printed in only the CMYK inks. 

Limitations of CMYK Printing

Although the CMYK ink combinations can produce more than 16,000 colors, they can't produce as many colors as the human eye can see. As a result, you may view colors on your computer monitor that can't be accurately reproduced using the process inks when printing on paper. One example is fluorescent colors. They can be accurately printed using fluorescent ink, but not using CMYK inks.

In some cases, such as with a company logo where the color must match exactly all other instances of that logo, CYMK inks might give only a similar representation of the color. In this case, a separate solid color ink (usually a Pantone-specified ink) must be used.

Preparing Digital Files for Printing

When preparing digital files for commercial printing, it is smart to convert the color space of your RGB images and graphics to the CMYK color space. Although printing companies do this automatically for you, making the conversion yourself allows you to be aware of any dramatic color shifts in the colors you see on-screen, thus avoiding unpleasant surprises in your printed products.

If you use full-color images in your project and must also use one or two Pantone spot colors to match a logo, convert the images to CMYK, but leave the spot colors specified as solid color inks. Your project then becomes a five- or six-color job respectively, which increases the cost of consumables and printing time. The price of the printed product reflects this increase.

When CMYK colors are displayed on-screen, such as on the web or in your graphics software, they are just approximations of what the color will look like when printed. There will be differences. When color is critically important, request a color proof of your project before it is printed.

CMYK is not the only full-color printing process, but it is by far the most common method used in the U.S. Other full-color methods include ​Hexachrome and 8C Dark/Light, which use six and eight ink colors respectively. These methods are used in other countries and in special applications.