Raster-image processing is the conversion of vector (digital) information into a high-resolution, pixelated ('raster') image. A raster-image processor, or RIP, whether a software or firmware component, is able to interpret vector data, such as a PostScript file, as an input language, transforming it into a single bitmapped image, or output language, ready to be printed.

The principal function of a raster-image processor is to produce an image that can be output for visual inspection, either on paper (plain or photographic), on some sort of visual display, or directly to film or printing plate [1].

Adobe's 1984 partnership with Allied Linotype, an established and respected manufacturer of typesetting equipment and typefaces, saw the realisation of the first RIP-enabled PostScript typesetter, the Linotype Linotronic 100, and later the Linotype Linotronic 300: imagesetters, as they would become known, capable of outputting resolutions of 1,270dpi and 2,540dpi [2]. In the first of these machines, a standalone raster-image processor was incorporated to interpret PostScripted page-description data, and produce a high-resolution, continuous-tone bitmap-image film that could be chemically transferred to a lithographic printing plate – a process known as computer-to-film, or CTF, imagesetting. 

Raster-image printing, or laser printing, is another innovation to come from Xerox PARC, with the first laser printer being released as part of the Xerox Star 8010 computer system in 1981 [3]. Utilising a mechanism similar to that of a xerographic or photographic copier, it succeeded the daisy wheel and dot-matrix office computing standards (in which rasterised or bitmapped graphics are mechanically printed on to a substrate through an ink ribbon) as a non-impact process whereby graphics are printed a pixelated line at a time, without the paper or substrate being physically struck. This produced instantly superior results, yet it would be some years before output could be considered professional typeset quality. Capable of printing multiple fonts at hitherto unseen high resolutions, the impact laser printers had upon the office environment assured the technology of their role in the revolution to come [4].

Notes

1. Seybold J., 1984. The world of digital typesetting. Media PA: Seybold Publications Inc. p.374

2. Pfiffner P., 2003. Inside the publishing revolution: the Adobe story. San Jose: Adobe Press, p.43

3. In 1984 Hewlett-Packard introduced its Laserjet printer for the PC, which was capable of printing resolutions of 300dpi, producing near-typeset-quality outputs at a fraction of the cost of the alternative, 'daisy wheel' impact printers of the time. The first laser printers, conceptually introduced in the mid-1970s, were text-orientated and in the $500,000 price range. On launch in 1979, Canon released its LBP-10 for $10,000. The HP Laserjet at that time cost $3,600 (Spring M., 1991. Electronic printing and publishing: the document processing revolution. New York: Marcel Dekker, p.171).

4. In commercial printing, in order to produce higher-quality images for proofing purposes, plotters are used, printing vector images – as opposed to raster graphics – based on the same laser-etching mechanism. 

Tom O’Reilly worked in the Academic Books Production department of Cambridge University Press, 2007–2014.

This blog comprises excerpts from his book What You See Is What You Get: Desktop Publishing And The Production Revolution at Cambridge University Press (1980–1996).