Page Description Languages - PDL

Earlier on in history, printers viewed text as text, and graphics as graphics. A page was created from a combination of separate entities. The page images can be created by having raw text like, the word “Hello World”, combined with Escape codes and possibly embedded graphic pictures. Different programs have different file formats.

To overcome this problem, Page Description Language (PDL) is developed. PDL is a language to describe the graphical representation of ink and toner on sheets of paper (or other output devices, like monitors, photo typesetters, etc) in a higher level than an actual output bitmap.

Instead of sending raw text to the printer, a PDL output file is created and sent to the printer. Basically PDL instructs the printing device exactly how to handle text, graphics, and pictures in reproducing the page layout created by a computer user. The ‘page’ could be of any size, color, or resolution the printing device can handle.

By having PDL, an application programmer could concentrate on making his program to output result in a standard PDL - with description of his printable page. The printing device developers could focus on making their devices with related PDL literate.

Various PDL exist. Example of PDL are Adobe Postscript (one of the most popular PDL), PCL (“Print Control Language”, from Hewlett-Packard), “ESC/P” (from Epson) and GDI (“Graphical Device Interface” from Microsoft).

PDL files can be textual or binary data streams. If a printer supported the related PDL, it means that there is a specialized processor within the printer is functions as an interpreter for that particular PDL. This PDL interpreter will processes the supplied file and creates the requested page image. The printer’s drawing engine then takes the image and draws it on the page.

The appearance of these PDL eased life, and facilitated further development for everybody.