GREYSCALE HALFTONE

A greyscale halftone image simulates varying intensity levels by modulating the size and spacing of individual dots. Typically, 0% corresponds to fully clear (no dots), and 100% represents fully black (maximum dot coverage). Because our imaging process is binary—capable only of producing either exposed or unexposed pixels—we cannot produce true continuous-tone greyscale. Instead, halftone rendering provides an effective approximation for most applications.

Halftoning works by making the dot size and/or spacing vary in response to grey level: smaller dots for lighter areas, larger dots for darker tones. This technique is distinct from dithering, where dot size remains constant and only the density or distribution changes. In halftoning, the grey effect is achieved through pulse-width modulation (dot size variation) and frequency modulation (dot spacing). The result appears as a smooth tone when viewed with an optical system or by the human eye—provided the individual elements are below the system’s resolution limit.

PIXEL AND RESOLUTION

Halftone resolution is measured in lines per inch (LPI), referring to the number of dot rows within one inch. Higher LPI values allow for finer detail and smoother tone transitions. We offer four standard screen resolutions, but custom values can also be specified to meet unique spatial frequency requirements. For comparison, standard laser printers typically use 65 LPI, while professional book printing may reach 150 LPI.

The table below provides example dot sizes for various greyscale percentages at different screen resolutions. At 1000 LPI, a 20% tone consists of 13 µm dark dots on a clear background, while a 90% tone consists of 6 µm clear dots in a dark area. Dot polarity (dark-on-clear vs. clear-on-dark) is adjusted to maintain fidelity across the greyscale range.