Technology of Desktop Publishing
Technology of Desktop Publishing
Desktop publishing (DTP) relies on two primary hardware components: 1) a computer, supplemented by various input devices including scanners and cameras, and 2) a printer that can produce high quality typographical and pictorial output. The process of on-screen DTP page composition is made possible by WYSIWYG (what you see is what you get) page layout software for personal computer use, and page description languages, programming that bridges the gap between the page layout software and the printers that produce pages that match what the user sees on the computer screen.
The DTP Computer
The two key technological features of a DTP computer are an inexpensive personal computer with a graphical user interface (GUI) based on windows, icons, menus, and point-and-click actions, and WYSIWYG page layout software.
The personal computer is at the heart of the DTP process. The development of inexpensive, powerful Macintosh computers with easy-to-use graphical user interfaces, based on windows, icons, menus, and pointing (WIMP) provided the driving force behind the development and rapid implementation of DTP applications throughout the 1980s. The key feature of this technology was the graphics (bit-mapped) display that allowed a user to manipulate text and graphics on an electronic page, using a combination of the mouse and the keyboard as input tools, and to see an accurate representation of the page on the computer screen as the layout work progressed.
Composing text on a page has always been a complicated process. Computer software, running on mainframe computers, made this somewhat easier, but early programs did not provide for the use of variable width type, specialized formatting, or artwork, or the ability for the user to see a reasonable image of what the page would look like when printed. As specialized systems for publishing were developed, these concerns were addressed, but the programs were complicated to use, requiring mastery of complex formatting instruction language. In addition, the specialized machines were expensive and beyond the means of any but the largest printing enterprises.
Word processing software running on personal computers in the early 1980s was easier to use, and provided some previewing capabilities, but it did not have the functionality required for typesetting, and, without the availability of bit-mapped screens, it could not represent typefaces, exact placement, or art work.
Before long, however, word processors were able to compose variable typefaces and take advantage of emerging powerful graphical user interfaces for previewing and manipulating page layout. The first commercially significant software application for page layout that exploited the graphical user interface and included powerful layout capabilities for arranging and paginating content, was Aldus PageMaker, which was first available for use on the Macintosh computer. Today, other important DTP page layout systems include QuarkXpress, Ventura, Interleaf, and FrameMaker.
The DTP Printer
The two key technological features of a DTP printer are a high resolution, all-points-addressable, matrix marking engine, and a high-function page description language.
High Resolution Printing.
The products of late nineteenth- and early twentieth-century printing were aesthetically satisfying, but awkward and time-consuming to produce. The process was based on the use of metal type counters for type and engraving techniques for diagrams and art. Phototypesetting, which emerged later in the twentieth century, used optical and chemical techniques for typesetting, which improved functionality and maintained high-quality results, but still required very expensive equipment and highly trained operators.
Early computer printing reverted to solid type counters and mechanical inking techniques; these printers were fast, but they had a limited range of typically fixed-width typefaces that resembled typewriter output. Furthermore, they limited the user's ability to place type on the page and so were far below the functionality and quality needed for publishing. Mechanical matrix printers that used a matrix of striking pins—commonly called dot-matrix printers—could more easily create variable-width type-faces and even crude artwork, but the low resolution of the mechanical matrix and the limitation of the mechanism meant that the results, although adequate for office documents and business communications, were still well below traditional typesetting requirements.
DTP printers, on the other hand, use laser and ink-jet technologies and rely on marking techniques that organize the entire page into a very fine-grained matrix with more definition than is possible with a matrix of mechanical pins. This allows for the high resolution imaging of different typestyles and of both line and gray-scale bit-map graphics.
The first computer printer to use this technique was the Xerox 9700, a 300 dpi ("dots per inch") laser printer released in 1979. The impact of this first commercial laser printer was limited in part by a lack of software that could take advantage of its functionality. In 1979 computer composition was based on batch processing , with little support for graphics or printing preview. The 9700's internal software for operating it in all-points-addressable mode could not be accessed by most existing composition or text processing software. Finally, the 9700, with a 120-page per minute printing engine and a price of around $350,000, was too expensive to have much impact beyond its intended market of high-volume printing firms.
In the early 1980s, another high-resolution matrix technology appeared commercially as part of a Hewlett-Packard ink-jet printer. Its price was about $6,000. However it was the Apple Laserwriter, a 300 dpi laser printer designed for the Macintosh computer, that ultimately inaugurated the DTP era in 1985. The Laserwriter's incorporation of the Postscript page description language gave it extraordinary functionality that fully exploited the capabilities of the high-resolution matrix engine.
In the early days of DTP, 300 dpi resolution was arguably still well below the visual quality available from traditional typographic printing services. As a result, the expression "near typeset quality" became common to describe output produced by these printers. However when the resolution rose to 600 dpi, and font designs and page description languages improved, many purchasers of typesetting services began to feel that the difference in quality between traditionally printed and DTP-produced pages was slight, and not worth the cost of selecting the more expensive traditional option.
Page Description Languages.
Early computer printing typically involved machinery such as physical type counters, each of the same width, which made an ink impression on paper by striking an intervening ribbon. Although the software that composed lines and pages did not need to be as sophisticated as it is now because characters were the same width and relatively few specialized layout features were used, the software that actually operated the printers was even simpler. But while such printing was adequate for data or internal office communications, it did not offer the functionality or quality required by general publishing.
With the development of laser and ink jet printers that could compose high resolution characters and images by placing tiny dots of ink or toner anywhere on the page, both the composition software and the printer software had to become much more sophisticated to utilize the capabilities of such printers more fully. At the same time, a proliferation of printers, each with its own physical requirements, required each word processing or page layout software application to output different kinds of data files for every kind of printer. It was complex and expensive to match user needs with exactly the right combination of computer and printer hardware and software programs that would lead to the desired printed product.
In the 1970s John Warnock, working at Xerox's Palo Alto Research Center (PARC), developed Interpress, a language for the control of high-resolution matrix marking. Warnock became dissatisfied with Xerox's marketing of Interpress and he left the company to form Adobe Systems. In 1984 Adobe released a page description language, Postscript, designed to provide precise programmable and device independent control of page images. This precise programmable control could exploit high-resolution marking engines to produce scaleable high-quality diagrams and artwork as well as aesthetically satisfying typography.
In addition, the possibility of single printer language interface for communication between printers and page layout software simplified the engineering of both. Today almost all publishing systems are Postscript based, with word processing or page layout software producing a Postscript data stream (representing the formatted text), which is then sent to Postscript-based printers, where it undergoes "raster image processing" (RIP), which converts the programming instructions to a bitmap page image.
Beyond the Printed Page
With the advent of electronic publications in CD-ROM (compact disc-read only memory) and World Wide Web formats, DTP page layout systems are now designed to import and export XML -encoded content to be integrated with XML-based publishing. Material can be prepared simultaneously for dissemination in multiple formats. With continuing improvement in this area, DTP will continue to play an effective role in the emerging ecology of networked information.
see also Desktop Publishing; Document Processing; Integrated Software; Markup Languages.
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