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Halftones
Halftone photography uses a special halftone screen or software designed for converting images for printing. The original halftone screen consisted of ink lines on
two sheets of flat glass glued together at a special angle. The glass screen is now obsolete as most halftones are produced with contact sheets or are electronically created.
Screens with a ruling of 60 to 100 lines per inch (lpi) are used to make the halftones you see in newspapers. The dots that make the image are very coarse and make for a rough picture. Screens with 120 to 150 lpi
are what you see in most magazines and commercial printing. 150 to 500 lpi screens are used for photo quality process color printing like you might see in posters or cd covers.
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