PostScript

PostScript
Adobe Systems · Public domain · source
Name	PostScript
Developer	Adobe Systems
Released	1982
Operating system	Unix, MS-DOS, Windows, macOS
Platform	x86, ARM, PowerPC
Genre	Page description language
License	Proprietary

PostScript PostScript is a page description language and programming language developed for electronic and desktop publishing. It served as a foundational technology for laser printers, typesetting systems, and digital imaging workflows used by organizations such as Apple Inc., Adobe Systems, and Hewlett-Packard. The language integrated concepts from programming languages and graphics systems pioneered in environments including Unix, Xerox PARC, and academic research at institutions such as Stanford University and MIT.

Overview

PostScript combines a stack-based programming model derived from languages like Forth with vector graphics primitives similar to drawing models used in Sketchpad research and Display PostScript approaches from Xerox PARC. It became central to workflows involving devices from manufacturers such as Canon Inc., Epson, Ricoh, and IBM. Standards and file formats influenced by the language include specifications adopted by ISO and print workflow technologies used by companies like Agfa-Gevaert and Kodak. PostScript competed with, complemented, or influenced systems such as TeX, PDF, SGML, and OpenType.

History and Development

Development began at Adobe Systems in the early 1980s by engineers including John Warnock and Charles Geschke, who had prior experience at Xerox PARC and worked with technologies related to Interpress. The language's release coincided with products from Apple Inc. (notably the Apple LaserWriter) and partnerships with Hewlett-Packard that expanded adoption in offices and print shops. PostScript's evolution included multiple levels and extensions, with contributions from vendors such as Linotype, Monotype Imaging, and academic groups at Carnegie Mellon University and University of Cambridge. Legal, standards, and market events involved entities such as United States Court of Appeals for the Ninth Circuit, Federal Trade Commission, and industry consortia like International Color Consortium.

Language Features and Syntax

PostScript is a concatenative, stack-based language with control structures influenced by languages such as Algol 68 and BCPL. Its syntax supports operations comparable to those in C for arithmetic and logical expressions, though execution is postfix with tokens pushed to an operand stack. Data types include arrays, dictionaries, strings, numbers, booleans, and procedures; these are manipulated using operators similar to paradigms from Smalltalk and Lisp. The language supports font handling compatible with formats developed by Adobe Type Manager, Linotype, and Monotype Imaging, and integrates with outline font technologies such as Type 1 fonts and CID-keyed fonts used by publishers like The New York Times Company and The Guardian. PostScript also exposes device-specific operators for printers developed by manufacturers including Xerox, Canon Inc., and Fuji Xerox.

Graphics Model and Imaging Model

The graphics model employs a device-independent imaging model with paths, stroking, filling, clipping, and transformations, echoing work by researchers at Xerox PARC and the graphics primitives used in PHIGS implementations. The imaging model separates coordinate systems, user space, and device space similar to approaches in Display PostScript and later adopted in Portable Document Format. Color models include DeviceGray, DeviceRGB, DeviceCMYK, and support for color management aligned with standards from International Color Consortium and systems used by Pantone and Agfa-Gevaert. The language supports Bézier curves, affine transforms, and compositing operations conceptually related to blending techniques in OpenGL and PostGIS-style spatial transformations. Printers from Hewlett-Packard, Epson, and Xerox implement rasterization pipelines influenced by the imaging model.

Implementations and Tools

Commercial and open implementations include interpreters and RIPs from Adobe Systems, third-party products from Gutenprint maintainers, and RIP engines by Global Graphics and Harlequin. Open-source projects such as Ghostscript provide interpreters and conversion utilities used in toolchains alongside editors like Adobe Illustrator, CorelDRAW, and layout systems such as QuarkXPress and Scribus. Development tools and SDKs have been provided by companies like Agfa-Gevaert, Kodak, and Monotype Imaging, and system integrations exist for Microsoft Windows Server, Linux, and macOS Server. Print production environments from houses such as Condé Nast, Hearst Communications, and academic presses at Oxford University Press used RIPs and workflow systems interoperating with prepress tools like Prepress suites and color workflows managed using X-Rite hardware.

Uses and Influence

PostScript shaped desktop publishing, digital typesetting, and prepress processes employed by publishers such as Penguin Books, HarperCollins, and Oxford University Press. It influenced rival and successor formats including Portable Document Format developed by Adobe Systems and page description concepts in XPS from Microsoft. The language's model informed graphics subsystems in operating systems including macOS, NeXTSTEP, and windowing systems from Sun Microsystems used in desktop publishing suites like Aldus PageMaker and graphics applications such as Photoshop and InDesign. PostScript-based workflows were central to industries served by companies like FedEx Office, Staples, and commercial printers such as RR Donnelley.

Criticisms and Limitations

Critics cited performance, security, and predictability issues; complex programs could trigger long render times on low-memory devices such as early models from Canon Inc. and Epson. Portability challenges arose across device implementations from vendors like Hewlett-Packard and Ricoh, leading to rasterization inconsistencies affecting clients including The New York Times Company and The Washington Post. The language's Turing-completeness raised concerns similar to debates in communities around JavaScript and Perl regarding embedding full programming languages in document formats, which influenced moves toward declarative formats like PDF and standards set by ISO.

Category:Page description languages