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What is a Halftone Screen?

A printing press is only able to produce clear, defined images in the color of the ink on the press. In order to reproduce a wide range of continuous and intermediate tones of gray in a black and white photograph, the photograph must first be converted to an image that conforms to the limitations of the printing press. This conversion is done by the use of halftone screens.

In the past, a halftone screen was created by shooting a photograph through a screen of dots with a stat camera which converted the image into rows of tiny black dots. The size and intensity of the dots would be relevant to the darkness of the gray areas. Today, photographs can simply be scanned into a computer system and printed out with the halftone screens. The photo can be printed at whatever screen frequency you desire.

The dots created by the halftone screen create a sort of optical illusion. Because the dots are so small and are of varying proximity to each other, our eyes are fooled into seeing shades of gray when, in fact, all the dots are actually black. Halftone screens are measured by the number of lines of dots in an inch of the screen.

The halftone screen frequency, or linescreen, that one uses is dependent on the capabilities of the press and the paper being used. Presses that are used to print newspapers are only capable of handling a low linescreen such as 85 lines per inch (lpi). High-quality magazines use linescreens of 150lpi and up. The finer the linescreen (the more dots per inch), the better the reproduction quality and detail you'll see in the image.

However, a word of caution: a linescreen that is too high for a paper or press' capabilities, will result in a poor final print. The printed images will appear blotchy and muddy. Ask your printer what linescreen they prefer. It is important that you find out what linescreen will be used as you will need this information before ordering your printing film. The designer will also need to know the linescreen so that they can scan the images at the appropriate resolution.

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