What You Need to Know About Color Separations in Printing

Color separation is the process by which original full-color digital files are separated into individual color components for four-color process printing. Every element in the file is printed in a combination of four colors: cyan, magenta, yellow, and black, known as CMYK in the world of commercial printing.

Combining these four ink colors produces a wide spectrum of colors on the printed page. In the four-color printing process, each of the four color separations is applied to a separate printing plate and placed on one cylinder of a printing press. As sheets of paper run through the printing press, each plate transfers an image in one of the four colors to the paper. The colors—which are applied as minuscule dots—combine to produce a full-color image.

CMYK Color Model: For Print Projects

CMYK separation
Jon Sullivan/CC BY-SA 4.0-3.0-2.5-2.0-1.0

A commercial printing company handles the actual work of making the color separations on most projects. The company uses proprietary software to separate your digital files into the four CMYK colors and to transfer the color-separated information to plates or directly to digital presses.

Most print designers work in the CMYK model to more accurately predict the appearance of the colors in the final printed product. 

RGB: For Digital Projects

Hexadecimal Triplets for RGB Colors
 RGB colors use specific amounts of Red, Green, & Blue which may be expressed as Hexadecimal Triplets. Jacci Howard Bear

CMYK is not the best color model for documents destined to be viewed on a screen, however. These are best built using the RGB (red, green, blue) color model. The RGB model contains more color possibilities than the CMYK model because the human eye can see more colors than ink on paper can duplicate.

If you use RGB in your design files and send the files to a commercial printer, they are still color-separated into the four CMYK colors for print. However, in the process of converting the colors from RGB to CMYK, color can shift from what you see on screen to what is reproducible on paper.

Setting Up Digital Files for Color Separation

RBG CMYK conversion in Photoshop

Graphic designers should set up their digital files destined for four-color separation in the CMYK mode to avoid unpleasant color surprises. All the high-end software—Adobe Photoshop, Illustrator and InDesign, Corel Draw, QuarkXPress, and many others—offer this capability. It’s just a matter of changing a preference. 

An Exception to the Rule

Select the Color box in the New Spot Channel dialog.

If your printed project contains a spot color, that color should not be marked as a CMYK color. It should be preserved as a spot color so that, when the color separations are made, it will appear on its own separation and be printed in its own special-color ink. Programs such as Adobe Photoshop make this process quite easy.

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