PostScript
Introduction
PostScript is a page description language (PDL) used primarily in the electronic and desktop publishing areas. Developed by Adobe Systems in 1982, it is a dynamically typed, concatenative programming language with a rich set of graphic primitives. PostScript is notable for its ability to describe the appearance of text, graphics, and images on printed or displayed pages with high precision. It is a cornerstone technology in the field of desktop publishing and has played a significant role in the development of the modern printing industry.
History and Development
PostScript was created by John Warnock and Charles Geschke, co-founders of Adobe Systems, as a means to improve the quality and efficiency of printing processes. The language emerged from earlier work on a project called Interpress at Xerox PARC. Warnock and Geschke left Xerox to start Adobe and developed PostScript as a more flexible and powerful alternative.
PostScript gained rapid adoption due to its ability to produce high-quality printed output on laser printers, which were becoming increasingly popular in the 1980s. The introduction of the Apple LaserWriter in 1985, which included a PostScript interpreter, was a pivotal moment that helped establish PostScript as a standard in the industry.
Technical Overview
Language Characteristics
PostScript is a stack-based language, meaning that it uses a stack data structure to hold operands and results of operations. It is a dynamically typed language, allowing for flexibility in the types of data that can be manipulated. PostScript supports a variety of data types, including numbers, arrays, strings, and dictionaries.
The language is also concatenative, which means that functions and operations are composed by placing them in sequence, with each operation taking its arguments from the stack and leaving its result on the stack. This characteristic is shared with other stack-based languages like Forth.
Graphics Model
PostScript's graphics model is one of its most powerful features. It uses a device-independent coordinate system, allowing for precise control over the placement and appearance of graphical elements. The graphics model supports a wide range of operations, including path construction, painting, and clipping.
Paths in PostScript are constructed using a series of operators that define lines, curves, and shapes. These paths can then be painted using various fill and stroke operations. The language also supports transformations, such as scaling, rotation, and translation, which can be applied to graphical elements.
Text Handling
Text handling in PostScript is highly sophisticated, allowing for precise control over font selection, size, and positioning. The language supports a wide range of fonts, including both bitmap and outline fonts. PostScript's ability to handle text with such precision made it a popular choice for typesetting and publishing applications.
Applications and Uses
Printing and Publishing
PostScript has been widely used in the printing and publishing industries due to its ability to produce high-quality output on a variety of devices. It serves as an intermediary format that can be interpreted by printers to produce the final printed page. This capability has made it a standard in professional printing environments.
Desktop Publishing
The rise of desktop publishing in the 1980s and 1990s was closely tied to the adoption of PostScript. Software applications like PageMaker and QuarkXPress used PostScript to create complex page layouts that could be printed with high fidelity. The language's ability to handle both text and graphics with precision made it an ideal choice for these applications.
Graphic Design
In addition to its use in publishing, PostScript has been employed in graphic design applications. Designers use PostScript to create illustrations, logos, and other graphical elements that require precise control over appearance. The language's support for transformations and complex path operations makes it well-suited for these tasks.
PostScript Variants and Extensions
Encapsulated PostScript (EPS)
Encapsulated PostScript (EPS) is a variant of PostScript that is used to describe a single page of graphics. EPS files are often used to transfer graphic images between applications and systems. They include a preview image and a bounding box that defines the area of the graphic, making them suitable for embedding in other documents.
PostScript Level 2 and Level 3
PostScript has undergone several revisions, with Level 2 and Level 3 being the most notable. PostScript Level 2 introduced improvements such as better memory management, support for color printing, and enhanced font handling. Level 3 further expanded the language's capabilities with features like improved image compression and support for transparency.
Adobe PDF
While not a direct extension of PostScript, the Portable Document Format (PDF) was developed by Adobe as a successor to PostScript for document distribution. PDF retains many of the features of PostScript but is designed to be more efficient for viewing and sharing documents electronically. PDF files are often generated from PostScript files as part of the publishing workflow.
Technical Challenges and Limitations
Complexity and Learning Curve
One of the challenges associated with PostScript is its complexity. The language's flexibility and power come at the cost of a steep learning curve, particularly for those unfamiliar with stack-based programming. Writing PostScript code manually can be challenging, and errors can be difficult to diagnose.
Performance Considerations
PostScript's performance can vary depending on the complexity of the document and the capabilities of the interpreter. Large or complex documents may require significant processing time, particularly on older or less powerful devices. This has led to the development of optimized interpreters and hardware acceleration solutions.
Compatibility Issues
While PostScript is a standard in the printing industry, compatibility issues can arise due to differences in interpreter implementations. Variations in how different devices and software handle PostScript can lead to inconsistencies in printed output. This has been mitigated to some extent by the development of standards like PDF.
Future of PostScript
Despite the rise of newer technologies like PDF, PostScript remains a vital part of the printing and publishing industries. Its role as an intermediary format for high-quality printing continues to be important, particularly in professional environments. However, the focus has shifted towards PDF for document distribution and viewing.
Adobe continues to support PostScript, and the language is likely to remain relevant as long as there is a need for precise control over printed output. The ongoing development of printing technologies and the demand for high-quality output ensure that PostScript will continue to play a role in the industry.