PostScript

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.

The first version of the PostScript language was released to the market in 1984. The qualifier Level 1 was added when Level 2 was introduced.

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).

Laser printers combine the best features of both printers and plotters. Like plotters, laser printers offer high quality line art, and like dot-matrix printers, they are able to generate pages of text and raster graphics. Unlike either printers or plotters, a laser printer makes it possible to position high-quality graphics and text on the same page. PostScript made it possible to exploit fully these characteristics by offering a single control language that could be used on any brand of printer.

One issue is that fonts do not scale linearly at small sizes and features of the glyphs will become proportionally too large or small and start to look displeasing. PostScript avoided this problem with the inclusion of font hinting, in which additional information is provided in horizontal or vertical bands to help identify the features in each letter that are important for the rasterizer to maintain. The result was significantly better-looking fonts even at low resolution. It had formerly been believed that hand-tuned bitmap fonts were required for this task.

In the late 1990s, Adobe joined Microsoft in developing OpenType, essentially a functional superset of the Type 1 and TrueType formats. When printed to a PostScript output device, the unneeded parts of the OpenType font are omitted, and what is sent to the device by the driver is the same as it would be for a TrueType or Type 1 font, depending on which kind of outlines were present in the OpenType font.

Some basic, inexpensive laser printers do not support PostScript, instead coming with drivers that simply rasterize the platform's native graphics formats rather than converting them to PostScript first. When PostScript support is needed for such a printer, Ghostscript can be used. There are also a number of commercial PostScript interpreters, such as TeleType Co.'s T-Script.

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.

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.

A Hello World program, the customary way to show a small example of a complete program in a given language, might look like this in PostScript (level 2):

PostScript uses the point as its unit of length. However, unlike some of the other versions of the point, PostScript uses exactly 72 points to the inch. Thus:

For example, in order to draw a vertical line of 4 cm length, it is sufficient to type:

Most implementations of PostScript use single-precision reals (24-bit mantissa), so it is not meaningful to use more than 9 decimal digits to specify a real number, and performing calculations may produce unacceptable round-off errors.

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