halftones

Halftones are a reproduction technique that uses dots to simulate continuous-tone imagery in print and display. The basic idea is that the eye blends a pattern of small dots of varying size, spacing, or density into perceived intermediate tones, allowing a grayscale or color image to be reproduced with a limited number of ink colors or display elements.

In traditional printing, a halftone screen converts a continuous-tone photograph into a grid of dots. The dot size or density encodes brightness: larger or more numerous dots create darker tones. For color work, the image is separated into multiple channels (commonly cyan, magenta, yellow, and black) and each channel is halftoned with a separate screen angle to minimize moiré and improve color reproduction.

Historically, halftone methods were developed in the late 19th century and became standard for newspapers and magazines, enabling inexpensive mass reproduction of photographs.

Digital halftoning covers methods used in image processing and display. Ordered dithering (such as Bayer matrices) and error-diffusion techniques (for example Floyd–Steinberg) simulate gray levels on devices with limited depth. Stochastic or frequency-modulated screening uses random or near-random dot placement to reduce visible patterns and improve tonal range.

Key concepts include screen frequency (lines per inch), dot shape, and dot gain (how ink spread affects tone). Higher screen frequencies yield finer detail but require higher-resolution output and paper handling; dot gain can shift intended tones. Halftoning remains essential in traditional printing, color separation workflows, and digital displays that must convey grayscale or color information with limited levels.