Commercial Printing: What does “Halftone” mean?

estimated reading time: 4 minutes

What is a Halftone?

A Halftone refers to a printing technique that simulates continuous tone images - such as photographs - using a pattern of ink dots. Varying the size and spacing of the dots creates the illusion of gradients and shades within the design, with larger dots representing darker areas and smaller dots representing lighter areas. Almost all commercial printing presses produce images using the halftone technique.

Digital Images vs Printed Images

To better understand why commercial printing presses use halftones to create images, it will help to do a quick review of the difference between digital images and printed images.

Digital images, like those that appear on computer monitors or cell phone screens, are composed of tiny illuminated squares called pixels. Each pixel can emit different wavelengths of light, thus providing an almost infinite spectrum of colors and shades from which digital images can be created. Also, adjusting the color intensity across adjacent pixels allows the colors within an image to gradually transition from one shade to another. The smooth color gradients from one pixel to the next are why digital images are considered to be full-tone images.

Printed images, unlike digital images, do not have an almost infinite range of colors with which to work. Most commercial printing presses use only four ink colors - Cyan, Magenta, Yellow, and Black. These four ink colors are known collectively as CMYK process printing, the industry standard for producing full color printing.

Also, unlike digital images, printed images are made with only one level of color intensity. The printing press can only apply ink dots in various sizes, it cannot alter the brightness of the ink dots being applied. Therefore, shades of light and dark can only be achieved by using different sizes of ink dots - with smaller dots being perceived as a lighter color shade and larger dots being perceived as a darker color shade.

Though full color images created on a printing press appear to have smooth color transitions and shades of light and dark, it is actually an optical illusion. In reality, printing presses cannot produce full-tone images directly. Instead, printing presses use halftones to simulate the appearance of full-tone images.

The CMYK printing process is able to mimic full-tone imagery by applying the cyan, magenta, yellow and black inks in successive layers of halftone dots. Each color prints as a separate pattern of dots, placed at different angles to prevent moiré patterns and ensure a smooth final image.

Try this Quick Experiment…

Find an image that has been commercially printed, like a photo printed on a brochure, magazine, or postcard.

If you look at the photo with the naked eye, your brain will perceive it to be a full-tone image…with different shades of color flowing smoothly throughout the image. Now, use a jeweler's loupe or strong magnifier to view the same photo up close. Under extreme magnification, you will see that the photo is not a full-tone image at all. It is actually made up of distinct ink dots. Some of the dots will overlap each other and some dots will appear in isolation.

It is the sizing and spacing of these ink dots that tricks our eyes. So from a normal viewing distance we see a printed image made of multiple colors and continuous tones, but in reality there are only four colors of ink dots in various sizes.

How are the Halftones Created?

When a digital artwork file is submitted for printing, your printer's prepress department will use specialized software to analyze the colors within the file. The software then uses this information to create grids of halftone dots.

For full color images, the software separates the artwork file into four unique files of colored halftone dots (cyan, magenta, yellow, and black). This allows the printing press to lay down these four colors individually, recreating the full color images on the paper substrate.

Monochrome Printing

Though up to now we have discussed CMYK printing, the halftone technique is not just for printing full color images. Monochrome images are commonly printed using halftones. For example, Grayscale images are created using only the black ink color, varying the spacing and sizing of the halftone dots to give the illusion of gradient color transitions between multiple shades of gray.

A Final Word…

Halftone printing is the foundation of commercial printing. It not only allows a printing press to simulate continuous imagery, it also saves print customers money because it reduces the amount of ink required to print photographs with intricate details and gradients.

Have Questions? Color Vision Printing is here to help!

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