Postscript in a nutshell:

Adobe invented Postscript, a Page Description Language. This language describes all the contents of a page using text. This text is quite similar to programming and formatting languages such as Javascript or C++. It describes type, lines and shapes as vector formulas and the bitmap, or raster, graphics are described pixel by pixel.
Take a look at this example of Postscript code.

Graphic applications speak Postscript. Quark, Illustrator, Pagemaker, etc. create pages with Postscript.
When we select the Print command, the application sends a huge Postscript text file to an output device; in the lab this would be the HP Laserwriter.
Connected to or built into the output device is a computer whose job is to read and interpret the Postscript. This computer makes a raster graphic from the page description in the Postscript file and is called the Raster Image Processor…the “RIP” we hear mentioned frequently.

The HP Laserjet has its RIP built-in. The Epson Stylus 3000 has a software RIP separate from the printer, much like the RIPs used in print shops.

Tiny spots from Whoville

The raster image will be printed by the output device connected to the RIP. The RIP must make the raster page image to the same resolution as that device; for example, the HP Laserwriter makes 600 spots of toner every inch so the raster image will contain 600 pixels or spots per inch.

The imaging device is a machine which makes marks onto paper or film or plates. These marks may be tiny spots of toner powder, microscopic laser beams exposing photographic films or plates, or little squirts of ink in an inkjet printer. Imaging devices lay down row upon row of these ultra tiny marks to build the raster image we see as the graphic page.

They are so small that it takes hundreds of them to make just one halftone dot. It is as if the type and halftones are in our world and the imagesetter dots are from “Whoville”

Printing to a file

You can capture and save the Print command. The Postscript information we normally send to a desktop printer or an imagesetter can be saved into a file on the computer and we can use this file later.

Some people deliver the Postscript file to the print shop and the printers send the file into their imagesetter to create the film or plates. This can save time and eliminate errors if, and this is a big IF, the file has been prepared perfectly. The printer can’t make any changes to the Postscript file.

The most common use of saved Postscript page descriptions is in the creation of PDF documents. The Acrobat Distiller processes the information into Acrobat PDF documents. These PDF files can be read by any computer with the Acrobat Reader installed. Acrobat Reader is a free program made available for all the popular operating systems.