In printing , a technique of breaking up an image into a series of dots to permit reproduction of the full tone range of a photograph or artwork.
It is traditionally done by placing a glass screen printed with a tight grid of lines over the plate being exposed. The grid breaks up the image into hundreds of tiny dots, each of which is read by the camera as either black or white
or, in the case of colour art, as either a single printing colour or white. The resulting image, called a halftone, is then rephotographed for printing. Screens are made with a varying number of lines per inch, depending on the application; for newspapers the range is about 80–120, whereas glossy magazines usually require 133–175 lines per inch.