All color images like pictures and photographs are printed on an offset press with the four process color inks Cyan, Magenta, Yellow, and Black (CMYK -- K represents Black so not to be confused with B for Blue in RGB). These colors are also referred to as process colors, four color process, and even four color printing. These four process colors are combined on press with a technique called halftone screening to produce a visual simulation of all the colors of an image. In the examples below, we show you what the color separations look like individually, and then combined.

Cyan, Magenta, Yellow, and Black separations.

Composite process color image.

Most layout application use the CMYK color space for their default color usage. Some applications, however, use the RGB color space by default, like Microsoft® Office Publisher® 2007. It is important to convert the application Color Schemes to Process color (CMYK) before submitting to a commercial offset printer. Below we demonstrate how to convert the document colors to Process color (CMYK). For more information on how to convert Accent colors to Spot colors, follow this link.

While four color printing can simulate a wide variety of colors and is quite pleasing for images, it can also be limiting for some colors. The printed visual range of the CMYK color space is not as large as the visual color space of RGB. Or, in other words, you can see more colors on your monitor and in real life than you can on a printed page. The very tips of the RGB color spectrum are out of range in the CMYK color spectrum, and cannot be accurately represented in print. This is an important point to remember when printing color images. The most notable distinction is with saturated (the purest) reds, greens, and blues, they cannot be represented well with process colors. To learn more about this, you can review some of the basics in Color Theory and how it applies to offset printing.

Often More Economical

In many print shops, the process colors inks are the most commonly used and therefore can at times be even more cost effective than spot color printing. Often commercial printers have at least one press with the process color inks on it all day. Which translates to potential savings for you if the shop does not have to clean up and re-ink the press before printing your job. Having said that, I would like to stress the point of obtaining price quotes before creating your project. Process color printing can often be the most economical for your projects. If your project actually can be produced cheaper with process colors, then why not use the extra color capabilities provided with CMYK.

When to Use

Any time you want to print full color pictures or images you need to use CMYK colors. Additionally, if you want to use a wide variety of colors, you can theoretically use thousands of unique CMYK color builds and/or any spot colors that are converted to their CMYK equivalent values. By using CMYK color builds and converted spot colors you will only have used the four process colors, limiting your ink colors on press to four.

More Versatile

Given that with only four ink colors on press, you can print full color images, and thousands of unique colors, it is no wonder that the process colors are the most commonly used in the print industry. In days past, color separations and many of the processes required in the pressroom made process color printing cost prohibitive. However, today with desktop publishing, digital prepress, and more efficient presses, the cost barrier has been removed. More creative professionals are expanding the use of process color in their designs and opening up the potential that was once too expensive to explore.

Microsoft product screen shot(s) reprinted with permission from Microsoft Corporation.