It has become the printing and imaging technology of choice for corporations, publishers and government agencies throughout the world. 75 % of all commercial publications are printed on Adobe PostScript devices. These include
• black/white printers,
• colour printers,
• image setters,
• latesetters and
• direct digital printing systems.
By the way, Postscript is not limited to be used in printers or other devices used in the professional printing process. Also computer screens have been driven by Postscript.
The Postscripts language has had two major upgrades. The first version, known as PostScript Level 1, was introduced in 1984. Post script 1 was implemented by the Apple on the Apple LaserWriter printer. Postscript supported many new features at that time like outline fonts and vector graphics so it became popular among graphic printers. The structure of the Postscripts language, which is similar to a conventional computer programming language, meant that these advanced features could be used in a very versatile and creative manner to create complex images and designs. Apple continued to upgrade this language and introduced the Apple LaserWriter Plus. The new printer had more memory and many more outline fonts.
Nowadays, Postscript has become an industry standard for the typesetting of books, magazines and other complex publications.
PostScript Level 2
PostScript Level 2 was introduced in 1991, and included several improvements: improved speed and reliability, support for in-RIP separations, image decompression (for example, JPEG images could be rendered by a Postscripts program), support for composite fonts, and the form mechanism for caching reusable content.
The disadvantage of Postscripts was its speed. Postscript Level 1 required an enormous amount of processing power, and was often very slow. The capabilities of the various releases were also confusing, as the language was enhanced as each new printer was equipped with PostScript, extensions to PostScript were created to cope with colour, patterns, printers with multiple paper trays, duplex etc. PostScript Level 2 incorporates all the enhancements made to the original PostScript, setting a new baseline for the language. PostScript Level 2 is entirely backwards compatible with the original PostScript, and will produce the same image for a job as a PostScript Level 1 printer.
PostScript Level 3
Postscript level 3 was introduced in 1997, supports more fonts, better graphics handling, and includes several features to speed up PostScript printing.
PostScript 3 (Adobe dropped the "level" terminology in favor of simple versioning) came at the end of 1997, and along with many new dictionary-based versions of older operators, introduced better color handling, and new filters (which allow in-program compression/decompression, program chunking, and advanced error-handling).
The new graphics capabilities include
• smooth shading,
• idiom recognition,
• masked images,
• finer colour controls,
• superscreens, and
• fast image.
Other improvements of PostScript Level 3 include
• In–RIP Trapping,
• direct PDF printing, and
In–RIP Trapping is a new capability of the PostScript 3 interpreter that executes trapping commands at the raster image processor (RIP), automating complex and time consuming prepress tasks. Trapping is specified, then rendered at print time rather than as a separate production step prior to RIPping. Direct PDF printing is an optional capability of the Adobe PostScript 3 interpreter that improves workflow productivity by allowing the RIP to accept and print files in the Portable Document format (PDF) without
printing through an application – the PDF files don’t have to be opened with an application and then be printed from that application but can be sent directly to the RIP.
DeviceN is a new Level 3 operator that handles any number of colours, from duotones and tritones, to Haxachrome™ and beyond, in a composite workflow. This feature is supported by Adobe Photoshop 5.0. It makes prepress applications easier to use and
more efficient, representing all colour on one single page, instead of using one page per colour.
Quality. Adobe Postscript was designed from the outset to work seamlessly with every major operating system and color management system and prints anything, from everyday business correspondence to complex colorful brochures. The printed version always looks exactly as it does on-screen without reformatted pages or misplaced artwork.
Network. With support on every major computer platform Adobe Postscript devices are ideal for networks large and small.
- PostScript became commercially successful due to the introduction of the graphical user interface, allowing designers to directly lay out pages for eventual output on laser printers. However, the GUI's own graphics systems were generally much less sophisticated than PostScript; Apple's QuickDraw, for instance, supported only basic lines and arcs, not the complex B-splines and advanced region filling options of PostScript. In order to take full advantage of PostScript printing, applications on the computers had to re-implement those features using the host platform's own graphics system. This led to numerous issues where the on-screen layout would not exactly match the printed output, due to differences in the implementation of these features.
Print documents regardless of printing device computer platform or operating system. This is device independence. Adobe Postscript language file is independent of the device that created it and the device that prints it.
Print documents not created by the user including documents sent by email imported from new media such as CD-ROM or downloaded from the Internet.
Select the best device for users' needs from a wide variety of Adobe Postscript devices currently available.
Print easily across networks large or small which incorporate a variety of computers operating systems, applications and printing systems anywhere in the world.
Adobe Postscript printers and systems work independently of any network configurations ensuring seamless operation in any environment.
Print in color with the assurance that regardless of device the colors in the output will be what the user intended.
Performance. Adobe continuously optimizes the Adobe Postscript system to enhance performance. The flexibility of Adobe Postscript offers manufacturers the freedom to optimize the printing environment with technologies such as memory reduction compression and coprocessors.
Compatibility. Whether using Microsoft Windows Apple Macintosh, UNIX, OS/2, DOS, or a networked combination, Adobe Postscript delivers consistent high-quality results.
- Typically, PostScript programs are not produced by humans, but by other programs.
1. Faster printing and improved quality
2. New features to support the increasingly complex documents available via the Internet, such as three-dimensional images.
3. For complex documents, PostScript Level 3 processes each component as a separate object to optimize imaging throughput.
4. The resident font set will be expanded to provide compatibility with the resident fonts of all leading operating systems, enhancing performance by reducing font downloading.
5. PDF has been integrated into Adobe PostScript Level 3.
6. Ease of use, ease of connection and ease of printer management all in one environment, including Web based printer management, support for all industry standard remote management technologies, and a single step CD-ROM installer for all drivers, fonts and value-added software.
7. PlanetReady Printing: Allows printing technology to meet local language needs world-wide.
PostScript is an object-oriented language, meaning that it treats images, including fonts, as collections of geometrical objects rather than as bit maps. PostScript fonts are called outline fonts because the outline of each character is defined. They are also called scalable fonts because their size can be changed with PostScript commands. Given a single typeface definition, a PostScript printer can produce a multitude of fonts. In contrast, many non-PostScript printers represent fonts with bit maps. To print a bit-mapped typeface with different sizes, these printers require a complete set of bit maps for each size.
The principal advantage of object-oriented (vector) graphics over bit-mapped graphics is that object-oriented images take advantage of high-resolution output devices whereas bit-mapped images do not. A PostScript drawing looks much better when printed on a 600-dpi printer than on a 300-dpi printer. A bit-mapped image looks the same on both printers.
Every PostScript printer contains a built-in interpreter that executes PostScript instructions. If your laser printer does not come with PostScript support, you may be able to purchase a DIMM that contains PostScript.
It can contain any combination of text, graphics, and images. An EPS file is the same as any other PostScript language page description, with some restrictions.
An EPS file must be a conforming file, that is, it must conform to the Adobe Document Structuring Conventions (DSC). At a minimum, it must include a header comment,%!PS-Adobe-3.0 EPSF-3.0, and a bounding box comment,%%BoundingBox: llx lly urx ury, that describes the bounds of the illustration. (The specification does not require the EPSF version, but many programs will reject a file that does not have it.)
The EPS file should make no environment-sensitive decisions (the importing application may be trying to attain some special effect, and the EPS program shouldn't mess this up), although it can use some device-dependent tricks to improve appearance such as a snap-to-pixel algorithm.
The EPS file must not use operators that initialize or permanently change the state of the machine in a manner that cannot be undone by the enclosing application's use of save and restore (eg. the operators starting with "init" like initgraphics). As a special case, the EPS program may use the showpage operator. The importing application is responsible for disabling the normal effects of showpage.
The EPS file can contain any combination of text, graphics, and images. An EPS file is the same as any other PostScript language page description, with some restrictions.
EPS files also frequently include a preview picture of the content, for on-screen display. The idea is to allow a simple preview of the final output in any application that can draw a bitmap. Without this preview the applications would have to directly render the PostScript (PS) data inside the EPS, which was beyond the capabilities of most machines until recently. Another advantage of the image preview is that if the graphic contained by the EPS is not to be modified itself but e. g. only to be placed inside a page layout using a layout software, the computer has less work to display only the small size preview instead of the high resolution image.
There are three preview formats providing the preview option for different platforms:
• PICT (Apple Macintosh),
• TIFF (IBM compatible, especially Microsoft Windows),
• EPSI (platform independent).
PICT is a graphics file format introduced on the original Apple Macintosh computer as its standard metafile format. It allows the interchange of graphics (both bitmapped and vector), and some limited text support, between Mac applications, and was the native graphics format of QuickDraw. With the change to Mac OS X, PICT was dropped in favour of Portable Document Format (PDF) as the native metafile format, though PICT support is retained by many applications as it is so widely supported on the Mac.
A widely used bitmapped graphics file format developed by Aldus and Microsoft that handles monochrome, gray scale, 8-and 24-bit color. TIFF allows for customization, and several versions have been created, which does not guarantee compatibility between all programs.TIFF files are compressed using several compression methods. LZW provides ratios of about 1.5:1 to 2:1. Ratios of 10:1 to 20:1 are possible for documents with lots of white space using ITU Group III and IV compression methods (fax).
Portable Document Format (PDF)
Portable document format, a universal computer file format that preserves all the fonts, formatting, colors, and graphics of any source document, regardless of the application and platform used to create it; the open de facto standard for electronic document distribution worldwide.
A PDF file delivers the single “digital master” for use in electronic, printed, and mixed workflow environments, ensuring a consistency across all media types. The Adobe PDF file format is ideally suited for technical publications, as it can include photographic images, diagrams, graphs etc. The PDF document can be widely distributed across many computer platforms. To read the PDF format, you require a copy of the Adobe acrobat reader, which can be obtained free of charge from the Internet or from many magazine publications on distributed CD–ROM.
The PDF combines three technologies:
1. A sub-set of the PostScript page description programming language, for generating the layout and graphics.
2. A font-embedding/replacement system to allow fonts to travel with the documents.
3. A structured storage system to bundle these elements and any associated content into a single file, with data compression where appropriate.
PostScript Printer Descriptions (PPDs)
PostScript Printer Description (PPD) files are created by vendors to describe the entire set of features and capabilities available for their PostScript printers. It is a small file that contains information about the characteristics of a certain PostScript printer. These informations are used by the PostScript printer driver to provide full access to the printer’s features