PostScript

The concepts of the PostScript language were seeded in 1976 by John Gaffney at Evans & Sutherland,[2][3][4] a computer graphics company. At that time Gaffney and John Warnock were developing an interpreter for a large three-dimensional graphics database of New York Harbor.

Concurrently, researchers at Xerox PARC had developed the first laser printer and had recognized the need for a standard means of defining page images. In 1975-76 Bob Sproull and William Newman developed the Press format, which was eventually used in the Xerox Star system to drive laser printers. But Press, a data format rather than a language, lacked flexibility, and PARC mounted the Interpress effort to create a successor.

In 1978 John Gaffney and Martin Newell then at Xerox PARC wrote J & M or JaM[5][6] (for "John and Martin") which was used for VLSI design and the investigation of type and graphics printing. This work later evolved and expanded into the Interpress language.

Warnock left with Chuck Geschke and founded Adobe Systems in December 1982. They, together with Doug Brotz, Ed Taft and Bill Paxton created a simpler language, similar to Interpress, called PostScript, which went on the market in 1984. At about this time they were visited by Steve Jobs, who urged them to adapt PostScript to be used as the language for driving laser printers.

In March 1985, the Apple LaserWriter was the first printer to ship with PostScript, sparking the desktop publishing (DTP) revolution in the mid-1980s. The combination of technical merits and widespread availability made PostScript a language of choice for graphical output for printing applications. For a time an interpreter (sometimes referred to as a RIP for Raster Image Processor) for the PostScript language was a common component of laser printers, into the 1990s.

However, the cost of implementation was high; computers output raw PS code that would be interpreted by the printer into a raster image at the printer's natural resolution. This required high performance microprocessors and ample memory. The LaserWriter used a 12 MHz Motorola 68000, making it faster than any of the Macintosh computers to which it attached. When the laser printer engines themselves cost over a thousand dollars the added cost of PS was marginal. But as printer mechanisms fell in price, the cost of implementing PS became too great a fraction of overall printer cost; in addition, with desktop computers becoming more powerful, it no longer made sense to offload the rasterization work onto the resource-constrained printer. By 2001, few lower-end printer models came with support for PostScript, largely due to growing competition from much cheaper non-PostScript ink jet printers, and new software-based methods to render PostScript images on the computer, making them suitable for any printer; PDF, a descendant of PostScript, provides one such method, and has largely replaced PostScript as de facto standard for electronic document distribution.

On high-end printers, PostScript processors remain common, and their use can dramatically reduce the CPU work involved in printing documents, transferring the work of rendering PostScript images from the computer to the printer.

PostScript became commercially successful due to the introduction of the graphical user interface (GUI), 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.

As computer power grew, it became possible to host the PS system in the computer rather than the printer. This led to the natural evolution of PS from a printing system to one that could also be used as the host's own graphics language. There were numerous advantages to this approach; not only did it help eliminate the possibility of different output on screen and printer, but it also provided a powerful graphics system for the computer, and allowed the printers to be "dumb" at a time when the cost of the laser engines was falling. In a production setting, using PostScript as a display system meant that the host computer could render low-resolution to the screen, higher resolution to the printer, or simply send the PS code to a smart printer for offboard printing.

However, PostScript was written with printing in mind, and had numerous features that made it unsuitable for direct use in an interactive display system. In particular, PS was based on the idea of collecting up PS commands until the showpage command was seen, at which point all of the commands read up to that point were interpreted and output. In an interactive system this was clearly not appropriate. Nor did PS have any sort of interactivity built in; for example, supporting hit detection for mouse interactivity obviously did not apply when PS was being used on a printer.

When Steve Jobs left Apple and started NeXT, he pitched Adobe on the idea of using PS as the display system for his new workstation computers. The result was Display PostScript, or DPS. DPS added basic functionality to improve performance by changing many string lookups into 32 bit integers, adding support for direct output with every command, and adding functions to allow the GUI to inspect the diagram. Additionally, a set of "bindings" was provided to allow PS code to be called directly from the C programming language. NeXT used these bindings in their NeXTStep system to provide an object oriented graphics system. Although DPS was written in conjunction with NeXT, Adobe sold it commercially and it was a common feature of most Unix workstations in the 1990s.

Sun Microsystems took another approach, creating NeWS. Instead of DPS's concept of allowing PS to interact with C programs, NeWS instead extended PS into a language suitable for running the entire GUI of a computer. Sun added a number of new commands for timers, mouse control, interrupts and other systems needed for interactivity, and added data structures and language elements to allow it to be completely object oriented internally. A complete GUI, three in fact, were written in NeWS and provided for a time on their workstations. However, the ongoing efforts to standardize the X11 system led to its introduction and widespread use on Sun systems, and NeWS never became widely used.

The PDF and PostScript share the same imaging model and both documents are mutually convertible to each other. Both documents produce the same result when printed. The difference between the PDF and PostScript is that the PDF lacks the general-purpose programming language framework of the PostScript language. A PDF document is a static data structure made for efficient access and embeds navigational information suitable for interactive viewing.[10]^: 9

PostScript is a Turing-complete programming language, belonging to the concatenative group. Typically, PostScript programs are not produced by humans, but by other programs. However, it is possible to write computer programs in PostScript just like any other programming language.[11]

PostScript is an interpreted, stack-based language similar to Forth but with strong dynamic typing, data structures inspired by those found in Lisp, scoped memory and, since language level 2, garbage collection. The language syntax uses reverse Polish notation, which makes the order of operations unambiguous, but reading a program requires some practice, because one has to keep the layout of the stack in mind. Most operators (what other languages term functions) take their arguments from the stack, and place their results onto the stack. Literals (for example, numbers) have the effect of placing a copy of themselves on the stack. Sophisticated data structures can be built on the array and dictionary types, but cannot be declared to the type system, which sees them all only as arrays and dictionaries, so any further typing discipline to be applied to such user-defined "types" is left to the code that implements them.

The character "%" is used to introduce comments in PostScript programs. As a general convention, every PostScript program should start with the characters "%!PS" as an interpreter directive so that all devices will properly interpret it as PostScript.

 %!PS
 /Courier             % name the desired font
 20 selectfont        % choose the size in points and establish 
                      % the font as the current one
 72 500 moveto        % position the current point at 
                      % coordinates 72, 500 (the origin is at the 
                      % lower-left corner of the page)
 (Hello world!) show  % stroke the text in parentheses
 showpage             % print all on the page

 %!PS
 (Hello world!) =

0 0 moveto 
0 113.385827 lineto stroke

/cm {72 mul 2.54 div} def               % 1 inch = 2.54 cm exactly
 0 0 moveto
 0 4 cm lineto stroke

List of software which can be used to render the PostScript documents:

• Ghostscript
• pstoedit
• Zathura

• Adobe StandardEncoding (PostScript character set)
• Document Structuring Conventions
• Typeface
• Computer font
• Encapsulated PostScript
• PostScript Printer Description (PPD)
• Printer Command Language (PCL)
• LaTeX

• Adobe Systems Incorporated (February 1999) [1985]. PostScript Language Reference Manual (PDF) (1st printing, 3rd ed.). Addison-Wesley Publishing Company. ISBN 0-201-37922-8. Retrieved 2021-12-24.{{cite book}}: CS1 maint: url-status (link) (NB. This book (PLR3) together with the Supplement (PDF), archived from the original (PDF) on 2016-03-05, retrieved 2006-04-29 is the de facto defining work on PostScript 3 and is informally called "red book" due to its red cover.)
• Adobe Systems Incorporated (1990) [1985]. PostScript Language Reference Manual (2nd ed.). Addison-Wesley Publishing Company. (NB. This edition (PLR2) covers PostScript Level 2 and also contains a description of Display PostScript, which is no longer discussed in the third edition.)
• Adobe Systems Incorporated (1985). PostScript Language Reference Manual (1st ed.). Addison-Wesley Publishing Company. (NB. This edition (PLR1) covers PostScript Level 1.)
• Geschke, Charles (1986) [1985]. Preface. PostScript Language Tutorial and Cookbook. By Adobe Systems Incorporated (27th printing, August 1998, 1st ed.). Addison Wesley Publishing Company. ISBN 0-201-10179-3. 9-780201-101799. Retrieved 2017-02-27. (NB. This introductory text is informally called "blue book" due to its blue cover.)
• PostScript language program design. Adobe Systems. Archived from the original (Zip) on 2011-06-13. (NB. This book is informally called "green book" due to its green cover.)
• The Type 1 Font Format (PDF), Adobe, archived from the original (PDF) on 2015-03-21 (NB. This book is informally called "black book" due to its black cover.)
• PostScript vs. PDF, Adobe, archived from the original on 2016-04-13 (NB. Official introductory comparison of PS, EPS vs. PDF.)
• A First Guide to PostScript, Tail recursive
• Casselman, William ‘Bill’. Mathematical Illustrations: A Manual of Geometry and PostScript (PDF).
• Reid, Glenn (1990). Thinking in PostScript (PDF). Colorado, USA: Addison-Wesley. (NB. A thorough tutorial available online courtesy of the author.)