Let me be clear that I have been a proponent of the PDF file and Acrobat back to the 1990s when Adobe invited me to test a bit of software based upon their whitepaper Camelot. It was the early version of what was to become the PDF file. It was a really interesting time, internet was just on the way in, and the whole idea was that a PDF file could be an office document that would require as little internet bandwidth as possible. While this was simple with ASCI text for example, maintaining a cross-platform document structure and formatting, and fonts, was a real challenge. The initial idea of what was to become the PDF file was basically a means to share a document in an identical format amongst many platforms. That was great, but it was just the basics. The first PDF files were only RGB colour, no spot colours, and well, let us just say it was not made for prepress or printing.

But they asked me (and a lot of other early industry experts) a lot of questions about what we felt needed to be in the PDF file that was missing. The list I provided was long, as the initial PDF files were all about tiny files, and about the culling of that excessive image data for CMYK or high-resolution. I and others insisted that CMYK colours, spot colours, trapping, bleeding, trimming and many other prepress-specific roles were essential. Slowly, Adobe began to implement the features that we all said we needed. The initial goal of a PDF file was to make as small a file as possible, and it was not to be as focused upon high-quality graphic integrity. As they made new PDF versions, Adobe began to add these essential features into PDF and Acrobat. Accordingly, the PDF specification (which is publicly available for developers) is capable of a good many features that we are just now making use of. One of these is the Optional Content Group (OCG).

I am not a PDF nerd like you. What is so important about the OCG?

The OCG is a means to declare elements of a PDF file to be of a specific type or characteristic. In order to understand the value of that, one needs to understand what a normal PDF file is. A PDF file is an amalgam of graphic elements and font references. A normal PDF file has no means to declare that specific graphic elements (let’s say a barcode or a die-line element in a PDF file) are anything other than those, and cannot treat them individually. To a normal PDF file, a barcode is just any other vector or raster element. It cannot be treated in any automated or specific manner than any other element like it in the file. To a normal PDF file, a user can only define page-based bleed, trim or bounding-box parameters. So, in a normal PDF file, if your artwork is not based upon an AE4 or Letter-sized page, you have to manually impose PDF content for plates or digital output.

Packaging is all about the OCG

An OCG can define that a specific vector element from Adobe Illustrator or a CAD file for example, is a die. That die element can be used by an imposition tool to automatically fill a sheet of media with content or die-aligned PDF content. You can use a die element of an OCG to perform that automated imposition, because with an OCG, you can say “This vector element in the PDF file is a die, and therefore is used to align that content to the die in the imposition template. A barcode is another excellent use-case. In the barcode example, a preflight solution could be used to confirm that a barcode element has not been scaled less than 80 per cent for example, or that it has enough boundary in the margin outside the bars. A normal PDF file cannot tell the preflight process what is a barcode and what is a logo. But an OCG can tell a PDF file what types of elements are what types of content, and that is valuable to efficiency and automation in digital printing.

Why am I just now hearing about this?

Well, it has been around for a long time (more than 15 years) in the PDF specification, but it lacked industry guidance such as has been provided by the Ghent PDF Workgroup. If you are not familiar with this workgroup, it is responsible for the specifications of PDF variants for print and prepress. The PDF/X 1,2,3,4 are all PDF guidelines that are developed by the workgroup in order to somewhat standardise the PDF world. There are a million ways to make a PDF file, and only a few work perfectly for professional print processes. The Ghent PDF Workgroup is responsible for these.

The Ghent Workgroup recently announced a new version of its Processing Steps, which builds upon the OCG in a means to better define a non-page based PDF file, and to be able to define automation parameters for imposition. The announcement is available at this link: http://www.gwg.org/ghent-workgroup-releases-new-pdf-processing-steps-specification/

This is particularly key to packaging and other mission-critical prepress tasks that are common in its world. Automated imposition alone is a reason to take a serious look at the OCG, and why it might well be your preferred customer-delivery method. 

There is nothing really wrong with PDF as a result after all. It is really more a matter of best practices which is what the Ghent PDF Workgroup is all about. The work that they have done with the OCG is important because it will allow us true automation of the most complex of digital print evolutions, packaging. There is a lot of manual operation in even modern digital prepress. The OCG is working to put that to an end for good.

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