In printing, a halftone is the reproduction of a continuous-tone image (such as a photograph) using dots of varying sizes. Halftone dots are typically round, but can be any shape. In addition to varying in size, halftone dots can also vary in spacing (known as screen ruling), which creates different levels of tonality. The screen ruling is measured in lines per inch (lpi).
To create a halftone image, the original continuous-tone image is first converted into a series of dots of varying sizes. This is done by scanning the image with a halftone screen, which is a transparent sheet of film with a regular pattern of dots. The screen is placed over the image, and the image is exposed to a strong light source. This causes the dots on the screen to act as a series of tiny lenses, projecting the image onto a photosensitive material (such as photographic film or paper).
Half-tone is a printing technique that combines dots of varying sizes to create a deliberate screen that is used to reproduce continuous-tone imagery in print. This technique is important because it allows for the reproduction of photos and other continuous-tone images, which otherwise would not be possible to print. Half-tone screens are created by first dividing an image into a grid of small squares or dots. The dots are then printed in a pattern that is determined by the screen ruling. The screen ruling is the number of lines per inch that are used to create the half-tone screen. The higher the screen ruling, the more dots there are per inch, and the finer the screen. A half-tone screen with a high screen ruling will produce a print with a higher dot gain, which means that the dots will appear to be larger and darker. A half-tone screen with a low screen ruling will produce a print with a low dot gain, which means that the dots will appear to be smaller and lighter. The half-tone technique is important because it allows for the reproduction of continuous-tone imagery, which otherwise would not be possible to print.