Twenty Years of PDF/X – Part III

This is a multi-part article looking into how PDF/X paved the way for future PDF standardization and how the PDF/X family of standards revolutionized the graphics art industry.

Part I: It started with PostScript

Part II: PDF tames PostScript and publishing

Part III: The continued development of PDF/X standards

Part IV: PDF/X in retrospect

Nothing Breeds Success Like Success
– The Continued Development of PDF/X Standards

The rapid acceptance and adoption of PDF/X-1a for reliable, successful publishing workflows in conjunction with rapidly advancing technological advancement in parallel with changes in the nature of print itself fueled the requirement for newer, more advanced PDF/X standards.

• There were significant updates to the Adobe PDF and later the ISO PDF specifications and the underlying imaging model. Some examples:
  • Adobe PDF 1.4 added robust support for live object transparency (including transparency groups and blending modes), a major “ask” from the creative community. Prior to PDF 1.4, transparency needed to be simulated by overprinting and/or “flattening” content into opaque objects (a process that often-yielded nasty image artifacts).
  • JPEG 2000 image compression support was added with Adobe PDF 1.5.
  • Optional Content Groups (supporting layers and other more advanced features) was added with Adobe PDF 1.5.
  • Object Streams and support of compression thereof was added with Adobe PDF 1.5 providing for much more compact PDF files in many cases.
  • Black Point Compensation. Long a proprietary feature of various vendors’ color management systems, official support for Black Point Compensation was added with the ISO PDF 2.0 specification.
  • Output Intents. With ISO PDF 2.0, the concept of Output Intents was expanded to allow for optional Mixing Hints dictionaries, optional Spectral Data dictionaries with CxF/X-4 spot color characterization data per ISO 17972-4:2015. Support for page-level Output Intents (overriding a document level Output Intent) was also added
  • Document Part Metadata. ISO PDF 2.0 officially added support for Document Part Metadata. In conjunction with page-level Output Intents, Document Part Metadata enables the use of a single PDF file with multiple page types with different printing conditions (substrates, colorants, etc.) for printing on one or more (typically digital) presses. Such metadata would be expected to conform with ISO 21812.
• Contrary to industry pundits, print is anything but dead. What is true is that what is printed, the graphical characteristics of what is printed, and how such printing is performed has dramatically changed since the PDF/X-1a was developed over 20 years ago. The “new” printing can be technically challenging. Some examples:
  • Today’s print jobs are increasingly for packaging, signage (including large posters and vehicle wraps), artwork, textiles, wall coverings, personalized marketing campaigns, etc.
  • The content of today’s print jobs is typically much more complex than the content of 20 years ago. Driven by digital photography and more capable tools design tools, color and sophisticated transparency effects are increasingly important for printing. This includes colors outside the typical CMYK gamut (often requiring additional colorants to address the expanded gamut requirements and imaging on non-traditional substrates).
  • The concept of a “print job” increasingly extends well beyond one or more single size pages printed on only one substrate (or paper type) on one press. For example, a book can include a cover, monochrome text pages on matte paper, fold-in pages, and color pages on thicker, glossy stock. A similar example is that of variable data printing with multiple pages, cards, envelopes, etc. being produced as part of a personalized mailer. These different page types may require pages “pulled” from different trays or even printing on multiple devices in parallel for subsequent assembly.
  • Printers no longer have the luxury of customizing a PDF file to properly render content on only one type of device located in one location. And those devices are much less often CtP (computer to plate) devices supporting offset printing; digital printing is an ever-increasing destination for print jobs, especially for short run and/or variable data jobs. If just for operational purposes, ICC color management is no longer optional or a luxury.
• We learn from the past. Some features that printers were afraid of or concerned about supporting in the past and were excluded in earlier PDF/X versions have turned out to really be necessary to support. These features obviously include ICC color management as well as some not so obvious features as annotations in some conditions (such as comments, mark-ups, forms, etc.)

Clearly, the PDF/X-1a from 2001 could not readily meet the needs of the ever-changing print publishing marketplace.

ISO TC 130, WG 2, TF 2 continued to develop new “levels” (versions) of PDF/X between 2002 and 2020. It is not the purpose of this series of articles to exhaustively cover the features of all these new PDF/X versions, but rather, to provide an overview of same. A simple table contrasting the most important of these versions follow these overviews.

PDF/X-3:2002

Based on Adobe PDF 1.3, PDF/X-3:2002 (ISO 15930-3:2002) added support for ICC color management for objects within the PDF file, not just the Output Intent. Supporting complete blind exchange, this PDF/X version is supported by major graphic arts applications and RIPs, experiencing some limited uptake in Europe. However, it had very little acceptance elsewhere (especially in North America).

PDF/X-1a:2003

Based on Adobe PDF 1.4, PDF/X-1a:2003 (ISO 15930-4:2003) was a technical revision of but substantially the same as PDF/X-1a:2001. There was no PDF/X-1 type of support. No new features were inherited from use of PDF 1.4. Although supported by major graphic arts applications and RIPs, this PDF/X version was effectively ignored by the graphics arts and print communities.

PDF/X-3:2003

Based on Adobe PDF 1.4, PDF/X-3:2003 (ISO 15930-6:2003) was a technical revision of but substantially the same as PDF/X-3:2002. No new features were inherited from the use of PDF 1.4. Although supported by major graphic arts applications and RIPs, this PDF/X version was effectively ignored by the graphics arts and print communities.

PDF/X-4

Based on Adobe PDF 1.6, PDF/X-4:2008 (ISO 15930-7:2008) and its update PDF/X-4:2010 (ISO 15930-7:2010) includes the color support provided by PDF/X-3 and added additional features of PDF 1.6 including limited support for layers (Optional Content Groups) as well as compressed object streams and some JPEG 2000 image compression support. It is currently the most appropriate PDF/X for content with any transparency effects.

The PDF/X-4 conformance level provides for complete blind exchange and is supported by major graphic arts applications and RIPs. Carefully created and with some limitations, PDF/X-4 files can concurrently comply and be tagged as compliant PDF/A-2 files for archiving. Although use of PDF/X-4 is disappointingly low, its use has been slowly increasing over the last several years.

The PDF/X-4p conformance level differs from PDF/X-4 in that it provides for externally-referenced Output Intents, thus not providing for complete blind exchange. Although supported by many RIPs, there is absolutely no support for PDF/X-4p in any major graphic arts applications. Its use appears to be limited to some custom applications and systems concerned with the relative size of embedded Output Intents within large collections of small PDF files.

PDF/X-5

Based on Adobe PDF 1.6, PDF/X-5:2008 (ISO 15930-8:2008) and its update PDF/X-5:2010 (ISO 15930-8:2010) are essentially special-purpose versions of PDF/X-4 supporting the same general features as PDF/X-4. None of the three conformance levels provide for complete blind exchange.

The PDF/X-5g conformance level provides external reference of content via the Reference XObject feature of PDF.

The PDF/X-5pg conformance level extends the functionality of PDF/X-5g by also allowing for externally-referenced Output Intents.

The PDF/X-5n conformance level is similar to PDF/X-4p with the exception that the externally-referenced Output Intent profile is an n-colorant ICC profiles conforming to ISO 15076-1.

At this point, there are no known major graphic arts applications supporting any of the PDF/X-5 conformance levels. There is some RIP/DFE support for PDF/X-5g and PDF/X-5pg (as part of such RIP/DFEs’ support of the PDF/VT-2 standard).

PDF/X-6

Based on ISO 32000-2:2020 PDF 2.0, PDF/X-6:2020 (ISO 15930-9:2020) extends the graphics support of PDF/X-4 to include a wide range of PDF 2.0 features including but not limited to support for Black Point Compensation, per page Output Intents (with optional CxF/X-4 spectral data), and Document Part metadata. Use of annotations within the visible area of a page as well as non-XFA forms, digital signatures, and some Actions are now allowed with some notable restrictions.

The PDF/X-6 conformance level provides for complete blind exchange. Carefully created and with some limitations, PDF/X-6 files can concurrently comply and be tagged as compliant PDF/A-4 files for archiving. The PDF/X-6 and PDF/A-4 standards were developed concurrently and care was taken in the standards development to ensure this commonality.

The PDF/X-6p conformance level differs from PDF/X-6 in that it provides for externally-referenced Output Intents, thus not providing for complete blind exchange.

The PDF/X-6n conformance level is similar to PDF/X-6p with the exception that the externally-referenced Output Intent profile is an n-colorant ICC profiles conforming to ISO 15076-1. Likewise, it does not provide for complete blind exchange.

Given that we are currently only one year out from publication of the PDF/X-6 standard, there are not yet any known major graphics applications supporting any of the PDF/X-6 conformance levels. The expectation / hope is that such support will be forthcoming within the coming year. Stay tuned!

There was one PDF/X standard that is not referenced above or in the comparison table below. That standard is or maybe better expressed as was PDF/X-2:2003 (ISO 15930-5:2003). Withdrawn not long after its publication, PDF/X-2 supported a form of OPI using Reference XObjects to access external content but also supported color in a manner similar to PDF/X-3. There are no known applications that supported PDF/X-2.

Recommendation for Today’s Use of PDF/X

The PDF/X-6 standard was developed to best support the future, complex PDF print publishing workflows from content design to rendering and finishing as well as continue to support current simpler workflows. However, due to the fact is that it will probably be a year or more before we see any support for PDF/X-6 creation in any major graphics applications, the recommendation is to use the PDF/X-4 standard which has quite robust support in all major graphics applications as well as RIPs / DFEs.

Standards for Variable Data & Transactional Publishing Based on PDF/X – PDF/VT

The “newer” PDF/X standards, beginning with PDF/X-4, provided the base for additional ISO standards supporting variable and transactional publishing and printing (VDP).

The PDF/VT standards ISO 16612-2:2010 Graphic technology — Variable data exchange — Part 2: Using PDF/X-4 and PDF/X-5 (PDF/VT-1 and PDF/VT-2) and ISO 16612-3:2020 Graphic technology — Variable data exchange — Part 3: Using PDF/X-6 (PDF/VT-3) define standards by which PDF files may be optimized in terms of size, performance, and operations for variable and transactional publishing and printing.

In the case of PDF/VT-1 conformance level, supporting complete blind exchange, the PDF files comply with the specification for and are tagged as PDF/X-4 files in addition to complying with and being tagged simultaneously as PDF/VT-1 files.

For the PDF/VT-2 conformance level supporting external content (i.e., not complete blind exchange), the PDF files comply with the specification for, and are tagged as, PDF/X-4, PDF/X-4p, PDF/X-5g, and PDF/X-5pg in addition to complying with and being tagged simultaneously as PDF/VT-2 files.

The PDF/VT-2 conformance level supports a MIME package of one or more PDF/VT-1 and/or PDF/VT-2 “chunks” each of which conforms to their respective PDF/VT conformance level.

For the PDF/VT-3 conformance level, supporting complete blind exchange, the PDF files comply with the specification for and are tagged as PDF/X-6 files in addition to complying with and being tagged simultaneously as PDF/VT-3 files.

Prior to the publication of the initial PDF/VT standards, VDP was supported by any number of non-PDF-based protocols, some of which were standardized (such as PPML) and others of which were proprietary to a particular printer vendor. These protocols were most often based to some degree on an underlying PostScript renderer and were not appropriate for the current era of pure PDF RIPs and DFEs.

Twenty Years of PDF/X continues with PDF/X in Retrospect.