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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:
- IPDS (invented by IBM)
- PCL (invented by Hewlett-Packard Corporation)
- PDF (invented by Adobe Systems Incorporated)
- PostScript (also invented by Adobe Systems Incorporated)
Usually, AFP, 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 (as opposed to AFP, PCL, or PostScript
output) for printing hard-copy documents.
How Does a Page-Description Language Fit Into a Workflow?
Today's state-of-the-art electronic-publishing
software and hardware allows for many different
workflow configurations.
We won't attempt to describe all of the
possible ways that page-description languages
are used. Instead, we'll describe two of
the most common situations.
SITUATION #1: You use word-processing
software
to write a letter. Then you use a laser printer
to print the letter on paper, and you mail it
via U.S. Mail.
Let's assume that you're using Microsoft Word
to write the letter. After you've finished
writing it,
you click on "File," then you
click on "Print," then you click
on "OK." Microsoft Word then generates
page-description-language code that describes the
contents of your letter; and your
computer sends the page-description-language
code to the RIP
inside your laser 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 or ink to draw text and graphics (if any)
on the paper.
SITUATION #2: You use page-layout
software to create a newsletter. Then you
convert the newsletter to PDF format and
distribute it via e-mail.
Let's assume that you're using QuarkXPress
to create the newsletter. After you've created it,
you instruct QuarkXPress make a PostScript
file containing a description of the text and graphics
in the newsletter. Then you use Adobe Acrobat Distiller
to convert the PostScript file to PDF format.
You e-mail the PDF file to each person on the
distribution list for the newsletter.
Some recipients of the newsletter simply use
the Adobe Acrobat software
or the Adobe Reader software
to open the PDF file read it on the computer
screen. Others
prefer to read the newsletter on paper, so
after opening the PDF file in Adobe Acrobat/Adobe
Reader, they click on
"File," then click on "Print,"
then click on "OK." The Adobe Acrobat/Adobe Reader
software generates page-description-language
code (probably either PostScript code or
PCL code, depending on the printer). The
computer sends the page-description-language
code to the RIP inside the printer. The RIP
rasterizes the code and sends the result of
the rasterization to the printer's print
engine, which prints the text and graphics
by depositing toner on the paper.
How Do You Determine Which Page-Description Language to Use?
In most situations, you don't really have to
worry about which page-description language to
use — provided that your computer system has
already been set up to work with the printer(s)
that you utilize. The software applications
that you use to create and print your
documents will
automatically generate
page-description-language code that is
appropriate for the printer(s) that you are
using. For example, if you are printing to a
Lexmark Optra printer, your application will
most likely create PostScript code when you
instruct it to print a document.
Some
printers can understand more than one
page-description language. For example,
lots of desktop laser printers can
understand both PostScript
and PCL. If
you have a
printer like this, your or your system
administration have probably already
decided what page-description language
you want your printer to use; and you or
the system administrator have probably
already set up your computer to tell your
applications to use that particular
page-description language when printing documents.
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