QUESTION: What is a page-description language?
ANSWER: A page-description language (PDL) is a computer language that describes the text and graphics in a document. Printers and RIPs understand page-description languages.
There are only a few page-description languages that are in widespread use today. Perhaps the best-known page-description languages are:
- AFP (invented by IBM)
- IPDS (also invented by IBM)
- PCL (invented by Hewlett-Packard Corporation)
- PDF (invented by Adobe Systems Incorporated)
- PostScript (also invented by Adobe Systems Incorporated)
Usually, AFP, IPDS, PostScript, or PCL is used when you are printing a document on paper; and PDF is used when you want a file that can be viewed on the screen by using 1) the Adobe Acrobat software, 2) a Web browser that is capable of displaying PDF files, or 3) some other software application that lets you view PDF files. However, you can also print PDF files on paper; and these days, more and more people are generating PDF output for printing hard-copy documents.
Here is an example of how a page-description langue fits into a workflow most of us are familiar with.
Let's assume you're using Microsoft Word to type a letter. After you've finished typing it, you tell Microsoft Word to print the letter on your laser printer. What happens when you do this is the following:
- Software on your computer known as a "printer driver" obtains a description of the letter's text and graphics from Microsoft Word.
- The printer driver translates this information into page-description language and sends the page-description-language code to the RIP inside your printer. (Depending on your printer, the page-description-language code will probably be either PostScript code or PCL code.)
- The RIP rasterizes the page-description-language code and sends the result of the rasterization process to the print engine in your printer.
- The print engine prints the letter by using toner to draw text and graphics on the paper.