PDF Emerges From PostScript

In the first of two articles on PDF, we'll trace the path of PDF from its beginnings as a format for the paperless office to where it is today. (See part II here.)

IF PDF documents have not affected your in-plant already, they will soon. Consequently, the future of your shop may depend on how much you learn about the Portable Document Format.

To help you, IPG is presenting a two-part article on PDF, detailing its history and application in both the ink-based and digital/toner environments.

Since PDF is a variation of PostScript, it's helpful to take a look back at the origins of this Adobe page description language.

In the beginning, the only way to get hard copy output from a computer was to print using a dot matrix or impact printer. The printer was basically an automated typewriter. These devices were expensive, slow and very limited in their ability.

PostScript actually has its roots in a language called "Interpress" developed at the Xerox Palo Alto Research Center (PARC). A scientist named John Warnock created Interpress, a computer-based language for describing documents. Xerox had just invented the laser printer, and an output device language was needed. Interpress was nearly identical in functionality to what would become PostScript.

Warnock and his boss, Chuck Geschke, immediately saw the value of a digital page description language. They lobbied the Xerox brass for two years, trying to get Xerox to license or market Interpress. Finally, out of frustration, they both left PARC to start their own company.

As an aside, the Xerox PARC lab is as famous for its creations as it is for lost opportunities. Other innovations PARC did not capitalize on:

• The computer mouse.

• Ethernet networking.

• The graphical user interface.

• The laser printer.

Creek Of Inspiration

After leaving Xerox, Warnock and Geschke started a new company named Adobe Systems, after a creek that ran behind Warnock's house. They considered creating and building large printers, but later decided to focus on developing tools for controlling printers.

The result: PostScript—a language used to control output devices like printers or imagesetters. PostScript was released in 1984. From the beginning it needed a powerful system to run it. In fact, during the first few years of existence, PostScript printers had more processing power than the Macintosh computers hooked up to them.

While PostScript started slow, it offered some huge advantages:

• PostScript was device independent. On a laser printer, you could get 300-dot-per-inch (dpi) output, while the same file could give you crisp 2,400-dpi output when sent to an imagesetter. Users were no longer tied to proprietary systems.

• Any manufacturer could buy a license for the PostScript interpreter and use it to build an output device. Thus, PostScript opened the door for competition and innovation.

PostScript was a pretty big gamble when it came out. Creating a "standard" as a small company is tough, and at the time many big companies had their own proprietary solutions.

In fact, the whole thing may have failed if it hadn't been for the CEO of Apple Computer, Steve Jobs. He invested a large sum of money in Adobe and convinced the firm to create a PostScript controller for the Apple LaserWriter.

A computer linked to a powerful printer would not have made much of an impact by itself, but Apple and Adobe were fortunate enough to stumble upon a third partner: a start-up company that created an application to utilize both the Mac and the LaserWriter to their full extents. The company was called Aldus, and the software product was PageMaker. This combination culminated in the birth of desktop publishing as we know it.

After this explosion, imagesetters soon began accepting PostScript, as it became an industry standard for describing a digital document for output.

New Versions Released

Still, despite being considered a standard, PostScript had considerable limitations. PostScript 2 added support for more features, including color and improved memory management.

Finally, Adobe released PostScript 3. In reality this revision was fairly minor. Even in 1998 many vendors were releasing products that were not fully PostScript 2 compliant, let alone 3. An interesting addition to PostScript 3 was the native support for PDF.

PostScript achieved exactly what it was created to do: provide a universal language for digital output. Over the years, proofing devices, imagesetters, direct imaging presses, digital presses and countless other devices have all been able to share the same input file because of this.

So Where Did PDF Come From?

PDF is actually an "extension" of PostScript that was created in 1993 to serve as a "Digital Paper." In fact, one way of looking at PDF is as a viewable PostScript.

Since it is an extension of PostScript, it inherits all of the benefits of PostScript that we discussed earlier.

One thing that PostScript never became, however, is a universal format for file exchanges. Instead, customers send their native application file from an application like Quark or PageMaker and include the resources, such as fonts and graphics. This all goes to a prepress area where it is reassembled and converted to PostScript and passed on to a digital output device like an imagesetter or printer. This has become known as a PostScript workflow.

Because the "exchange" can result in missing resources, a new workflow element was created: Preflight.

The chaos of making sure you got what the customer wanted you to get resulted in the introduction of the preflight checkpoint to make sure everything was in order before continuing in the production cycle.

While PostScript is perfect for output devices, it fails miserably when it comes to person-to-person transfer—especially with people that are not trained in graphic arts. And let's face it, more and more non-graphic artists are creating today' s production work.

Preflight slows things down dramatically. It's sort of like going through customs on an overseas trip. It doesn't matter if everything is in order; there is still going to be a slowdown while everything is checked.

What is really needed in a production environment is a universal format that is consistent, reliable, predictable and somewhat able to be edited—and easily exchanged.

The PDF file format was created to be the single file that contained everything you needed to view and output the document to any device. It has potential to be the universal standard that meets all of our needs.

So what are the major differences between PostScript and PDF files?

• PDF files are smaller than PostScript files. Smaller files are easier to send, store and manage.

• PDF files are more reliable than PostScript files—but, only if they are created properly.

• PDF files can include all of the resources for a document. This is the greatest strength. Instead of a collection of resources along with an application file, you get one file that can be viewed in a standardized "viewer."

• PDF files can be viewed with software that is free to anyone.

PDF files certainly sound like the perfect solution to many of the challenges we face: They are becoming a universal format; They are easy to share; They include all of the document resources; They co-exist with PostScript.

But does PDF really work?

In the real world, the usage of PDF files can have very different results in the offset and digital printing worlds.

To read part II of this article, click here.

Heath Cajandig is the digital production manager for the University of Missouri-Columbia. Before joining the university, he was a digital printing and document management consultant for Xerox. You can contact him at:

cajandigh@missouri.edu