Halvton

Halvton, or halftone, is a printing and imaging technique used to reproduce continuous-tone imagery through patterns of tiny dots. In monochrome work, the tonal value of each area is conveyed by the size and/or density of the dots: lighter areas use small or sparsely placed dots, darker areas use larger or more closely spaced dots. When viewed from a normal distance, the dots visually combine to create intermediate tones.

The technique relies on a halftone screen, a grid or plate that imposes a regular pattern of dots onto the image. The original continuous-tone image is converted into a dot pattern that, when printed with ink, yields apparent greyscale through optical blending. In color printing, separate halftone screens are used for each color channel (typically cyan, magenta, yellow, and black). The screens are angled relative to each other to avoid undesirable moiré and to produce full-color images.

Halftone methods evolved from simple screen-based systems in the late 19th century and became standard in newspapers and magazines by the end of that era. Over time, various screening techniques were developed, including amplitude-modulated (AM) halftones, frequency-modulated (FM) or stochastic screening, and modern digital halftoning used in raster image processors.

In the digital age, halftoning is performed by software and printers to simulate greyscales on digital displays and printed media. Common digital methods include ordered dithering, error-diffusion dithering, and clustered-dot patterns. While the underlying idea remains the same—to imitate continuous tone with discrete elements—advances have improved fidelity, color control, and print stability.