Prepress technicians and workersThe printing process has three stages—prepress, press, and binding or postpress. In small print shops, job printers may be responsible for all three stages. They do the composition and page layout of the material received from the customer, check proofs for errors and print clarity and correct mistakes, print the job, and attach each copy�s pages together. In most printing firms, however, each of the stages is the responsibility of a specialized group of workers. Prepress technicians and workers are responsible for the first stage, preparing the material for printing presses. They perform a variety of tasks involved with transforming text and pictures into finished pages and making printing plates of the pages. Typesetting and page layout have been greatly affected by technological changes over the years and, today, advances in computer software and printing technology continue to change prepress work. The old �hot type� method of text composition—in which molten lead was used to create individual letters, which were placed in frames to produce paragraphs and full pages of text— has become rare. Its successor, phototypesetting or �cold type� technology, is still used for some composition work, but it, in turn, is being rapidly replaced by computerized digital imaging technology. Customers today are able to provide printers with pages of material that look like the desired finished product they want printed and bound in volume. Using a process called �desktop publishing,� customers are increasingly using their own computers to do much of the typesetting and page layout work formerly done by prepress technicians. Many regular customers employ workers called desktop publishers to do this work. (A separate statement on desktop publishers appears elsewhere in the Handbook.) Other customers employ in-house graphic designers who do desktop publishing as part of their work, or send the work out to freelance graphic designers. (Graphic designers are discussed in the statement on designers elsewhere in the Handbook.) It is increasingly common for prepress technicians or other printing workers to receive files from the customer on a computer disk or submitted by e-mail, that contains typeset material already laid out in pages. The printing industry is doing more prepress work using complete �digital imaging.� Using this technology, prepress technicians called �preflight technicians� take material received on computer disks from customers, check it for completeness, and format it into pages using electronic page layout systems; even though the pages may already be laid out, they still may have to be formatted to fit the dimensions of the paper stock to be used. When color printing is required, the technicians use digital color page-makeup systems to electronically produce an image of the printed pages, then use off-press color proofing systems to print a copy, or �proof,� of the pages as they will appear when printed. The technician then has the proofs delivered or mailed to the customer for a final check. Once the customer gives the �OK to print,� technicians use laser �imagesetters� to expose digital images of the pages directly onto thin aluminum printing plates. Some customers continue to provide material to printers that is more suitable for cold type prepress technology. Cold type processing, which describes any of a variety of methods to create a printing plate without molten lead, has traditionally used �phototypesetting� to prepare text and pictures for printing. Although this method has many variations, all use photography to create images on paper. The images are assembled into page format and rephotographed to create film negatives from which the actual printing plates are made. In one common form of phototypesetting, printed text received from the customer must first be entered into a computer programmed to hyphenate, space, and create columns of text. Typesetters or data entry clerks may do the keyboarding of text at the printing establishment. (See the Handbook statement on data entry and information processing workers.) The coded text then is transferred to a typesetting machine, which uses photography, a cathode-ray tube, or a laser to create an image on typesetting paper or film. Once it has been developed, the paper or film is sent to a lithographer who makes the actual printing plate. With traditional photolithographic processes, the material to be printed is arranged and typeset, and then passed on to workers who further prepare it for the presses. Camera operators start the process of making a lithographic plate by photographing and developing film negatives or positives of the material to be printed. They adjust light and expose film for a specified length of time, and then develop the film in a series of chemical baths. They may load exposed film in machines that automatically develop and fix the image. The lithographic printing process requires that images be made up of tiny dots coming together to form a picture. Photographs cannot be printed without them. When normal �continuous-tone� photographs need to be reproduced, camera operators use halftone cameras to separate the photograph into an image containing the dots of varying sizes corresponding to the values of the original photograph. Color separation photography is more complex. In this process, camera operators produce four-color separation negatives from a continuous-tone color print or transparency. Because this is a complicated and time-consuming process, most of this separation work is instead being done electronically on scanners. Scanner operators use computerized equipment to capture photographs or art as digital data, or to create film negatives or positives of photographs or art. The computer controls the color separation of the scanning process and, with the help of the operator, corrects for mistakes or compensates for deficiencies in the original color print or transparency. Each scan produces a dotted image, or halftone, of the original in 1 of 4 primary printing colors—yellow, magenta, cyan, and black. The images are used to produce printing plates that print each of these colors, with transparent colored inks, one at a time. Superimposition of the images on the photos produces �secondary� color combinations of red, green, blue, and black that approximate the colors and hues of the original photograph. Where this process is still being used, film strippers cut the film of text and images to the required size and arrange and tape the negatives onto �flats�—or layout sheets used by platemakers to make press plates. When completed, flats resemble large film negatives of the text in its final form. Platemakers use a photographic process to make printing plates. The flat is placed on top of a thin metal plate coated with a light-sensitive resin. Exposure to ultraviolet light activates the chemical in parts of the plate not protected by the film�s dark areas. The plate then is developed in a solution that removes the unexposed nonimage area, exposing bare metal. The chemical on areas of the plate exposed to the light hardens and becomes water repellent. The hardened parts of the plate form the text and images to be printed. During the printing process, the plate is first covered with a thin coat of water. The water adheres only to the bare metal nonimage areas, and is repelled by the hardened areas that were exposed to light. Next, the plate comes in contact with a rubber roller covered with oil-based ink. Because oil and water do not mix, the ink is repelled by the water-coated area and sticks to the hardened areas. The ink covering the hardened text is transferred to paper. 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