What is Halftone?
A pattern of dots used to reproduce continuous-tone gradients in a printing process that can only deposit ink in binary (on/off) fashion. Essential for screen printing.
In detail
Halftoning is the printing-industry technique for simulating gradients with dots. Screen printing applies ink in binary fashion — a pixel either gets ink or it doesn't, no middle ground — so smooth gradients are impossible without halftoning. The halftone screen breaks the gradient into a pattern of dots whose size varies with the original tone: large dots in dark areas, small dots in light areas. The eye blends them at viewing distance into a continuous tone. Halftones are characterized by three parameters: LPI (lines per inch — dot density), screen angle (rotation of the dot grid, used to avoid moiré when multiple colors are overlaid), and dot shape (round, square, or elliptical, each producing slightly different visual character). Modern textile screen printing typically uses 30-65 LPI, with 22.5° as the dominant color screen angle and 45° offsets for additional colors.
Example
A photograph being prepared for a 4-color screen print: each color channel becomes a halftone screen at a different angle (22.5°, 67.5°, 90°, 45°) so when overlaid the dots interlock without forming visible moiré patterns. Up close the print looks like dots; from 3 feet away it looks like the original photograph.