Halftoning is a method of printing shades of tone using a single color ink.
By varying the size or density of dots, the eye can see a shade somewhere between the solid color and the color of the background paper.
The resolution of a halftone screen is measured in lines per inch (lpi). This refers to the number of dots per inch in the halftone screen, and should not be confused with ‘dpi – dots per inch’. The higher the number of dots, the finer the detail that can be reproduced.
Printers typically determine the lpi that’s best suited for the paper and printing process.
Digital imagery intended for print should ideally have at least twice the number of pixels as the lpi of the halftone screen being used.
For example, commercial printing processes typically use 150-175 lpi line screens. So, digital imagery needs to have a resolution of 300-350 pixels per inch for the best detail on press.
Conventional Halftone Screens
Also called ‘AM (Amplitude Modulated)’ Screens. The position of the dots are fixed, while the size of the dots vary to produce the illusion of tonality. Most printing processes use AM Screens.
Stochastic Halftone Screens.
Also called ‘FM (Frequency Modulated)’ Screens. The size of the dots are uniform, while the number of dots vary depending on the level of tone. FM screens have the advantage of reproducing subtle tones, but require specific presses and premium paper.