The PDF/X-4 file format

PDF is a very versatile file format. Unfortunately this also means that it is very easy to create PDF files that are completely useless in a prepress environment. The solution to this problem is to define a set of rules that forbid the use of certain PDF functions that are irrelevant for printing purposes and to enforce others that do improve its usefulness in prepress. This set of rules is called PDF/X, a series of well defined subsets of the PDF standard that promise predictable and consistent PDF files.

PDF/X-4 is one of the newest PDF/X flavors. This page covers:

  • What are PDF/X-4 files?
  • The various PDF/X-4 versions
  • Which other PDF/X flavors exist?
  • PDF/X is just the starting point
  • How to create PDF/X-4 files

What is a PDF/X-4 file?

PDF/X-4 files are regular PDF 1.6 files.

  • The use of transparency is allowed.
  • All color data can be grayscale, CMYK, named spot colors, RGB, Lab or ICC-profile based.
  • Image data can be 8-bit or 16-bit. 16-bit images are still rarely used and may cause issues with quite a few RIPs and workflows.
  • The use of layers is allowed. In PDF/X-4 these are not the ‘regular’ PDF layers (OCG or Optional Content Groups for the techies among us) but the more sophisticated OCCD layers (which actually combine multiple OCGs in a group). If a regular PDF has for instance a layer with comments and another one with contact information, both layers could be combined in a single ‘info’ OCCD layer. When I updated this page early 2008, there weren’t any workflows on the market yet with proper support for handling OCCDs. Meanwhile callas pdfToolbox is the first PDF tool that has proper support for them.

The following restrictions apply to PDF/X-4 files:

  • All fonts must be embedded in the file. Embedding OpenType fonts is allowed.
  • OPI is not allowed in PDF/X-4 files: all image data must be embedded.
  • Compliant files cannot contain music, movies or non-printable annotations.
  • If there are annotations (sticky notes) in the PDF, they should be located outside the bleed area.
  • The file should not contain forms or Javascript code.
  • Only a limited number of compression algorithms are supported, JPEG 2000 being one of them.
  • Encryption cannot be used.
  • Transfer curves cannot be used.

Next to things that are not allowed, there is also some information that needs to be present in a PDF/X-4 file but that you may not find in regular PDF files:

  • There is an extra line of information which indicates that the PDF file is a PDF/X-4 file.
  • There is a separate flag (meaning a switch that is either ON or OFF) that details whether the PDF/X-4 file has already been trapped or not.
  • PDF/X-4 files contain extra operators that define the bleed and trim area.
    • The MediaBox defines the size of the entire document
    • The ArtBox or TrimBox defines the extent of the printable area.
    • If the file is to be printed with bleed, a BleedBox must be defined. It must be larger than the TrimBox/ArtBox, but smaller than the MediaBox.
  • The file needs to contain an output intent which describes the intended printing condition. The output intent is either:
    • an ICC color profile. Profiles can be embedded or referenced (in such a case when ICC profiles are externally supplied, such a file is called a PDF/X-4p file).
    • an output condition identifier, which is simply a text description of the intended print specifications (e.g. FOGRA27).

PDF/X-4 versions

The PDF/X specifications are evolving standards, which regularly get adapted to deal with newer technologies and applications as well as changes in the graphic arts industry. That is why the full name of PDF/X implementations includes the year they were established.

  • The original PDF/X-4 standard was also referred to as PDF/X-4:2007.
  • Early 2008 PDF/X-4 became an official ISO standard: ISO 15930-7:2008. That version is called PDF/X-4:2008.
  • There have been some complaints about the way fonts and colors are defined in the 2008 specifications. That is why a minor update of the specs is expected to be released in 2010. Those specs will be called PDF/X-4:2010.

Which other PDF/X flavors exist?

Below are other PDF/X flavors that are either actively used in the market or may become popular in the future.

  • PDF/X-1a
    • The first standard, created for black&white, CMYK or spot color jobs.
    • This is a standard that originated in the USA but is also popular in Europe.
  • PDF/X-3
    • To print black&white, CMYK or spot color jobs
    • Files may contain RGB/LAB/… colors in which case the user’s color management system needs to convert these to CMYK.
    • This standard was developed in Germany and Switzerland. Its use also seems to be largely restricted to those countries.
  • PDF/X-5
    • Derived from PDF/X-4, allows external images.

PDF/X is just the starting point

If you think all of the above restrictions make sure that you get perfectly printable PDF files, think again. There are no rules in PDF/X that state that images need to have a certain resolution. A file with 50 dpi images can be a valid PDF/X file yet the printed result will be horrible if used for printing glossy magazines. PDF/X is meant to be a standard which is independent from the specific production requirements of a type of printing.

GWG is an industry organization which took the PDF/X standards and then added on top of that a set of rules to cover specific types of printing. There are standard for exchanging files for commercial printing, newspapers, packaging and digital printing.

If you want to get absolutely perfect PDF files for the type of jobs that you print, head over to the GWG site and check out their specifications. In a lot of countries, the national trade organizations recommend the use of the GWG standards to exchange files. Currently GWG is working on specifications based on PDF/X-4, which may still get released in 2009.

How to create or process a PDF/X-4 file

Some Adobe applications such as Acrobat 8 and InDesign CS3 include support for the draft-PDF/X-4 specifications. They are not fully compliant since the PDF/X-4 specifications still changed after the release of this software. Acrobat 9 and Creative Suite 4 are fully compliant.

PitStop Professional 7.52 is a preflight tool that can not only check for PDF/X-4 compliancy but that can also fix existing PDF files to make them PDF/X-4 compliant. callas software also markets PDF/X-4 compatible tools.

It is a safe assumption that many prepress workflows can cope with generic PDF/X-4 files, even though they may stumble when dealing with some of its advanced features.

Other sources of information

The Efficientworkflows blog has an interesting article on implementing a PDF/X-4 workflow.

9 August 2013

18 Responses to “The PDF/X-4 file format”

  1. MisterQ says:

    Laurens,

    Kom toevallig op uw site terecht ;-)

    Wat er voor PDF/X-4 niet bijstaat is dat dit de eerste standaard is die transparency toelaat.

    Q

  2. Laurens says:

    ‘Bedankt’ for the feedback – it made me realize that pages that are not yet linked to from the main structure of this site still get picked up and indexed by Google. You found a page that wasn’t supposed to be found because it wasn’t ready yet.

    I think it is OK now. I still have some time to tweak the content since PDF/X-4 usage is still in its infancy.

  3. Alex says:

    Laurens, In the paragraph wich says:
    –”The use of layers is allowed. In PDF/X-4 these are not the ‘regular’ PDF layers (OCG or Optional Content Groups for the techies among us) but the more sophisticated OCCD layers (which actually combine multiple OCFs in a group.”–

    Does you mean OCGs instead of OCFs?

    Thanks,
    Alex

  4. Alex says:

    Hi Laurens,
    I googled it up for OCCD. If I understood well, OCCD is a group of OCGs, but, What exactly stands for the acronym OCCD?

    TIA,
    Alex

  5. Alex says:

    Hi Laurens,
    I’m sorry Laurens. As now I’m reading in ISO 15930-7: OCCD is Optional Content Configuration Dictionary.

    A variant consists of one or more OCGs, which are associated through an Optional Content Membership Dictionary (OCMD) and an OCCD. Each OCCD determines which OCGs are grouped together to form a single variant.

    bye!

    • Laurens says:

      Wow, I never managed to get past the first chapter of any of the PDF specifications. Congratulations on getting that far! What I haven’t found yet (and most likely never will find) is an actual description of what this means with the current applications on the market. As far as I know only Callas ships a tool that can handle OCCD’s but other apps that support this type of feature are bound to appear sometime. I’ve been told packing apps from vendors like Esko might profit the most from this type of functions.

  6. Alex says:

    ;-D
    I have read the whole ISO 15930 family for writing a paper about PDF/X requirements and so. Sincerely, it was quite hard to understand the ISO languaje and a bunch of acronyms like OCCD, OCG, etc… But, OCCD today remains very abstract for me. Do you mean Callas PDFToolbox4?

    Laurens, Something to say about NChannel and DeviceN? What’s the difference? Here is a very little description: http://www.enfocus.com/actionlist.php?id=921

    I’m doing some test with PhotoShop multitone EPS + Indesing producing PDF in both ways: High Quality and PDF/X-1a. Then, looking at Pitstop inspector window, these objects will be NChannel or DeviceN depending the way you chose to produce the PDF.

    (sorry for burden you)

    Thank you!

  7. Jonny says:

    would PDF 4 da print out on an Igen 3 fine?or should expect problems?

    • Laurens says:

      Since PDF/X-4 is a file format that is specifically created for guaranteeing good output results, your question is rather odd. You could interpret it as ‘Is the workflow that drives my iGen 3 capable of processing PDF/X-4 files?’
      I have no answer to that question. In fact, I don’t even know what RIP of workflow you have in front of the iGen. Maybe others can chime in, otherwise that question is better asked in a prepress forum, such as on http://www.b4print.com/forum/

  8. Ian says:

    Its all very good to say that acrobat 9 and creative suite 4 are compatable with x4 files, but they all cost money that a lot of us do not have. Can you suggest an alternative?
    My problem is when trying to open an x4 file I get a grey screen and a blog stating that this file does not have a program associated with it, please install a program. If one is already installed, create an association in Default program control panel.
    If you have a suggestion please state it in plain english as all of these CMYKs, RGB/LAB/, and GWGs dont mean much to a computer hack like me.
    Any help would be appreciated???

    • Laurens says:

      I am not aware of any inexpensive or free creative software that can generate PDF/X-4 compliant files.
      It is a bit surprising that you claim to get an error about a missing program association when you try to open a PDF/X-4 file. Since such files simply end with the .pdf extension (they are PDF files after all), they should open with Adobe Reader or any other PDF viewer you may have installed on your system.

  9. judi says:

    If you have an rgb image in an InDesign file, and you ouput using these PDF/X-4 settings, is it okay for the printer? does it convert the image to cmyk since it says it is for printing?

    Thanks, Judi

  10. David C. says:

    I attended a seminar about PDF/X-4 organized by the GWG. Quite interesting, there is a lot of new info to be added here ;)
    The GWG are working on 2 versions of the PDF/X-4 specs:
    - a deviceCMYK version that only allows deviceCMYK without icc profiles and spot colors, but with support for transparencies.
    - a color managed version with full support for iccCMYK/iccRGB/Lab/Gray… and transparencies, note, deviceRGB is not allowed! An output intent must be specified.

    If I remember correctly, NChannel will be the preferred color space over DeviceN.
    With Adobe CS 5.5 you can create PDF/X-4 files, with proper layer support. CS 4 & 5 seem to be missing the layer support.

    Cross-media options are also being explored.

  11. CDL says:

    Very informative. Thanks!

    I do have a question that is not directly related to the subject. I am seeking a list of image formats that DO NOT support transparencies. (ie. .jpg, .bmp, etc..) I know there must be more and my google search parameters appear to be inadequate. =/

    Can anyone help?
    Thanks!

  12. Kirti Ahuja says:

    Thanx for the information guys

  13. Steve says:

    Cant seem to use PDFX-4 2010 in Distiller ?

    • Laurens says:

      Distiller 3 obviously can’t cope with PDF/X-4 :-)
      That is an interesting question. I assume you tried it with a recent version. I can image that Adobe’s thinking is that a modern PDF file format like PDF/X-4 cannot correctly be created starting from good old PostScript. PostScript lacks some color management data, cannot contain transparency, lacks support for some of the newer compression algorithms… so you could only create dummed-down PDF/X-4 files from it. The export option in InDesign however does have all of those capabilities so it can generate PDF files that use the PDF/X-4 functions to its fullest. Maybe that is the reason why Distiller has no direct support for PDF/X-4 while InDesign does.


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