halftone

Halftone is a reprographic technique that simulates continuous-tone imagery—such as photographs or shaded artwork—using patterns of discrete dots. In a halftone image, the size, spacing, or density of dots encodes light and dark areas, so varying dot arrangements create the perception of intermediate tones when viewed from a normal distance. The method is widely used for grayscale and color printing.

The halftone process developed in the late 19th century, with early practical methods attributed to Frederic Ives and colleagues. By the 1890s, newspapers and magazines adopted halftone reproduction, enabling affordable mass production of images. The basic idea is to convert a continuous-tone image into a dot pattern that can be printed with standard presses.

In practice, a halftone image is produced by superimposing a regular grid of tiny dots, whose diameters or spacing vary to represent shade. In color work, separate images are created for each color channel (typically cyan, magenta, yellow, and black) and printed with screens at different angles to minimize interference and produce full color.

Two common halftoning methods are amplitude-modulated (AM) and frequency-modulated (FM) screening. AM halftones vary dot size to convey tone on a fixed grid, while FM or stochastic halftones vary dot density more irregularly to reduce visible grid patterns. In the digital era, halftoning is performed by software using dithering, error diffusion, or clustered-dot algorithms, with screen frequency measured in lines per inch and dot gains affecting final appearance.

Halftoning remains essential in printed media, enabling economical reproduction of photographs and complex images, while also influencing artistic styles in print, manga, and graphic design.