Most printers simulate gray by using halftone dots printed on a grid; the grid cells are called halftone cells, and the grid rows are called lines or line screens. Each halftone dot is made up of printer dots. As the halftone cell fills up with printer dots, the halftone dot gets larger, resulting in a darker shade of gray.

Printer resolution determines the number of dots available to create the halftone dot. A printer with smaller dots can produce a wider variety of halftone dot sizes, allowing more shades of gray. Screen frequency also plays a role: As screen frequency increases, the halftone cell gets smaller, and so can hold fewer printer dots, resulting in fewer possible shades of gray. As a result, there is a trade-off between the number of possible gray levels and image coarseness.

Simulating continuous tone with printer dots

A.

Continuous tone simulated by line screen

B.

Line screen consisting of halftone dots in rows

C.

Halftone dots consisting of printer dots