Printed imagery in which shades of gray are represented by a minute pattern of dots of variable size.Related link: "The Illustrated Book Study" is a collaborative effort undertaken by Cornell University Library's Department of Preservation and Conservation and Picture Elements, Inc, and the Library of Congress. On its Illustrated Book Study Resolution Samples pages, visitors can examine digital images of prints of several types ? collotype, copper engraving, etching, halftone, lithograph, mezzotint, photogravure, steel engraving, and wood engraving ? at each of several resolutions ? dots per inch (DPI). Also see benday, lithography, moir?, screen, and stipple.