Halftone screening / screen ruling (LPI)
Turning photos into grids of larger and smaller dots so on-or-off ink can fake grey. LPI says how fine that dot grid is.
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What it is
A press can only put ink down or leave it off. There is no 40% grey ink, so continuous tone gets broken into a grid of dots that grow and shrink: big dots read dark, small dots read light, and your eye blends them at reading distance. Screen ruling, measured in lines per inch (LPI), is how fine that grid is.
Typical rulings: newsprint 85, coated sheetfed 150 to 175, high-end art books 200 to 300, screen printed apparel 45 to 65. Rule of thumb for image resolution: about twice the LPI, which is where the famous 300ppi for 150lpi comes from. Each process ink gets its own screen angle (roughly 15, 75, 0, and 45 degrees) so the four grids interlock into rosettes instead of clashing. Stochastic (FM) screening swaps the grid for randomly placed same-size dots and dodges angles entirely.
The other half of the story is aesthetic: cranking LPI way down to 20 or 30 turns dots into the Lichtenstein and Ben Day comic look, the risograph zine texture, the deliberately cheap newsprint feel. Gotchas: ink spreads on press (dot gain), so an LPI too fine for absorbent stock plugs the shadows into mud, and scanning already-printed halftone art screens it a second time and produces moire.
Ask AI for it
Convert this image to a classic amplitude-modulated halftone: round dots on a single grid rotated 45 degrees, coarse enough to be obvious at about 20 lines per inch (comic-book scale), dot size varying with tone from nearly touching in the shadows to pinpricks in the highlights. One ink color on off-white paper, hard black-and-white edges with no anti-aliasing or grey pixels, and keep the dot grid perfectly regular across the whole frame.