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Oct 1, 2012 12:00 AM
TO HECK WITH THE VDP BOTTLENECK
HOW PDF/VT CAN STREAMLINE PRODUCTION WORKFLOWS FOR DIRECT MAIL, TRANSACTIONAL AND TRANSPROMO JOBS
BY MARTIN BAILEY
PDF/VT is a hot topic these days. In a nutshell, it’s a standard for describing a file format based on PDF, specifically for delivery of jobs for variable data printing. The “VT” part of the name stands for “Variable and Transactional.” It was designed to address all VDP needs, from personalized specialty items, through direct mail, to phone bills and credit card statements.
PDF/VT was published as ISO 16612-2 in 2010, and the first implementations were shown at Ipex in that year, but it took until early 2012 for most of the commonly used document composition vendors to release products that support it. Like many of the other PDFbased standards, PDF/VT uses a file-centric approach. A PDF/VT file encapsulates all of the graphical content for a VDP print job and does so in such a way that an external job ticket can be associated with it to control how it’s processed in the print service provider’s systems. So what benefits does PDF/VT provide? It boils down to four things:
1. Robust content delivery.
PDF/VT builds on nearly two decades of work in CGATS and then in ISO to define the PDF/X standards for the delivery of print jobs. PDF/X-1a, PDF/X-3 and PDF/X-4 are now in common use, but primarily for the delivery of static print jobs. Those standards increase the reliability of printing workflows across multiple companies or sites by requiring that all fonts used are embedded and that all color is specified completely enough to preflight, proof and print correctly. All PDF/VT files must also be valid PDF/X files, so all of the experience encapsulated into those standards is automatically inherited.
2. Integrated data about page ranges.
A PDF/VT file can contain something called a “DPart” structure, which comprises a hierarchy of information about the various pages in a job (this is often called “metadata” because it’s data about data). A specific range of pages may be identified as a personalized catalog for a specific recipient of a direct mail campaign, for example. The next page can be marked as a cover letter to accompany the catalog for the same recipient. At the next level up in the hierarchy, the recipient’s title, address, etc. can be included, pulling all of the printed pieces that must be delivered together. In the level above that, metadata about all recipients within a ZIP code area can be pulled together, and the next level up might show which ZIP codes fall into the area covered by a specific distribute and print service provider site. The hierarchy is designed to be flexible and accommodate whatever data you need in your workflow. It can then be connected with a template-based jobticketing solution to control imposition, rendering, printing, finishing and fulfillment. This can be useful if you’re printing a very large number of relatively short jobs and need a way to ensure that your workflow is correctly configured for each one. But it is most important if you’re printing and fulfilling jobs where each recipient receives different numbers of pages, especially if the output needs to be bound and finishing equipment needs to respond to those differences.
3. Performance optimization hints.
Most rendering workflows designed for VDP include some form of optimization to reduce the amount of processing required for graphical page elements that are used multiple times in a job, so that the rendering process doesn’t slow the press down. Examples might be the background image on a direct mail postcard, the logo or an ad in a TransPromo piece, etc. Each workflow includes its own approach, and these vary in sophistication and effectiveness. Most of them try to render such elements only once, to cache the results of that rendering and then to reuse the cached results multiple times. PDF/VT tries to help in this process by defining some hints that can be written into jobs by the document composition tool as the file is created. These were designed to enable a rendering workflow to identify those reused elements more easily and to therefore make better decisions about caching strategies more quickly. Unfortunately, VDP is a market in which technology is developing so rapidly that the PDF/VT hints are already a little too simple and don’t offer much value to the best current rendering solutions.
4. Support for pseudostreaming.
Historically, data formats defined for transactional printing, such as AFP, have allowed for streaming print workflows, i.e., the first pages of the job can be printed while the composition system is still creating the definitions for later pages. A single PDF file is not well constructed to support streaming (the “optimized PDF” structures to support byte-serving from web sites should not be confused with streaming for print; the requirements are very different). PDF can, however, be used in a “chunking” workflow, where multiple PDF files are created, each containing one chunk of a single job. The first chunk might contain the pages for the first ten thousand recipients of a direct mail piece, for instance, with the next ten thousand recipients in the next chunk. This allows something very close to streaming to be achieved, by printing from one chunk while later chunks are still being written. The efficiency of this mechanism can be improved further by extracting any large shared graphics into a separate PDF file and referring to them from the chunks themselves, so that they only need to be delivered once instead of in every chunk. The PDF/VT standard includes a conformance level called PDF/VT-2, which is specifically designed to support this kind of chunking workflow. It’s even possible to bundle all of the chunks back together into one continuous stream, although that’s more likely to be a good choice for the light production end of the digital production print spectrum than for high-volume printing.
A SOLID FOUNDATION TO BUILD ON
The PDF/VT standard offers some real benefits for the construction of robust, flexible and efficient workflows, encapsulating rendering, printing, finishing and fulfillment. But files must still be constructed well to take advantage of those benefits. It’s important to understand what PDF/ VT offers and what it doesn’t.
Much of what I’ve described above is optional. You can make a perfectly valid PDF/VT file that doesn’t include the DPart structure or optimization hints. It can still be valid even if it’s not constructed in a well-optimized way, even if an image that appears on every page is included separately on every one of those pages, bloating the file and reducing the speed at which it can be processed at the print site. PDF/VT is not the silver bullet that will magically make all your frustrations around VDP print jobs go away, but it is a good foundation that best practice solutions and workflows can be built on.
IT’S BEST TO TEST…
When you’re evaluating a solution for variable data printing, whether it’s on the composition side or on the print site, support for PDF/VT is likely to be a good thing, but there’s no substitute for testing that solution to ensure that it meets your specific needs. At both ends there can also be configuration issues that can have a significant bearing on how efficient the results can be; it’s often worth asking if your vendors have guidelines on best practice and on integration with the other components in your whole workflow.
Martin Bailey is the Chief Technology Officer of Global Graphics Software. He’s also the UK’s principle expert to the PDF and PDF/VT committee in ISO and chaired the CGATS and ISO committees working on PDF/X for many years. Talk to Martin at B2MeMag.com/MB3.