The PDF/X-5 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-5 is one of the newest PDF/X flavors. This page covers:

  • What are PDF/x-5 files?
  • Which other PDF/X flavors exist?
  • PDF/X is just the starting point
  • How to create PDF/X-5 files

What is a PDF/X-5 file?

PDF/X-5 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.

The following restrictions apply to PDF/X-5 files:

  • 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-5 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-5 file.
  • There is a separate flag (meaning a switch that is either ON or OFF) that details whether the PDF/X-5 file has already been trapped or not.
  • PDF/X-5 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.
    • an output condition identifier, which is simply a text description of the intended print specifications (e.g. FOGRA27).

All of the above requirements are identical to the PDF/X-4. The main difference between PDF/X-4 and PDF/X-5 is that the latter allows external references for XObjects (read: images), ICC-profiles and fonts. This means that a PDF/X-5 file can be smaller than a PDF/X-4 file because all the images that are used in a file need to be included in a PDF/X-4 file while they can be stored externally in case of a PDF/X-5 file.

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-4
    • An updated version of PDF/X-3 which adds among others support for transparency and spot colors.

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 difital 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 investigating PDF/X-5 but it is too early to tell if it will be used for any future specifications.

How to create a PDF/X-5 file

As far as I know there currently (late 2008) isn’t any software on the market yet to either create or process PDF/X-5 files.

9 August 2013

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