Halftone

Halftone is the reprographic technique that simulates continuous-tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient-like effect. 'Halftone' can also be used to refer specifically to the image that is produced by this process. Halftone is the reprographic technique that simulates continuous-tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient-like effect. 'Halftone' can also be used to refer specifically to the image that is produced by this process. Where continuous-tone imagery contains an infinite range of colors or greys, the halftone process reduces visual reproductions to an image that is printed with only one color of ink, in dots of differing size (pulse-width modulation) or spacing (frequency modulation) or both. This reproduction relies on a basic optical illusion: when the halftone dots are small, the human eye interprets the patterned areas as if they were smooth tones. At a microscopic level, developed black-and-white photographic film also consists of only two colors, and not an infinite range of continuous tones. For details, see Film grain. Just as color photography evolved with the addition of filters and film layers, color printing is made possible by repeating the halftone process for each subtractive color – most commonly using what is called the 'CMYK color model'. The semi-opaque property of ink allows halftone dots of different colors to create another optical effect, full-color imagery. While there were earlier mechanical printing processes that could imitate the tone and subtle details of a photograph, most notably the Woodburytype, expense and practicality prohibited their being used in mass commercial printing that used relief printing. Previously most newspaper pictures were woodcuts or wood-engravings made from hand-carved blocks of wood that, while they were often copied from photographs, they more resemble hand drawn sketches. Commercial printers wanted a practical way to realistically reproduce photographs onto the printed page, but most common mechanical printing processes can only print areas of ink or leave blank areas on the paper and not a photographic range of tones; only black (or coloured) ink, or nothing. The half-tone process overcame these limitations and became the staple of the book, newspaper and other periodical industry. William Fox Talbot is credited with the idea of halftone printing. In an 1852 patent he suggested using 'photographic screens or veils' in connection with a photographic intaglio process. Several different kinds of screens were proposed during the following decades. One of the well known attempts was by Stephen H. Horgan while working for the New York Daily Graphic. The first printed photograph was an image of Steinway Hall in Manhattan published on December 2, 1873. The Graphic then published 'the first reproduction of a photograph with a full tonal range in a newspaper' on March 4, 1880 (entitled 'A Scene in Shantytown') with a crude halftone screen. The first truly successful commercial method was patented by Frederic Ives of Philadelphia in 1881. Although he found a way of breaking up the image into dots of varying sizes, he did not make use of a screen. In 1882, the German Georg Meisenbach patented a halftone process in England. His invention was based on the previous ideas of Berchtold and Swan. He used single lined screens which were turned during exposure to produce cross-lined effects. He was the first to achieve any commercial success with relief halftones. Shortly afterwards, Ives, this time in collaboration with Louis and Max Levy, improved the process further with the invention and commercial production of quality cross-lined screens.