PDF - What is a PDF/X-1a file?



The most basic question is not what is best, but who shall decide what is best.
Thomas Sowell

3rd PDF


What is a PDF/X-1a file?
PDF/X-1a files are regular PDF 1.3 or PDF 1.4 files to which a number of restrictions apply:
• All fonts must be embedded in the file.
• All color data must be grayscale, CMYK or named spot colors. The file should not contain any RGB, LAB,… data.
• OPI is not allowed in PDF/X-1a 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.
• 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-1a file but that you may not find in regular PDF files:
• There is a separate flag (meaning a switch that is either ON or OFF) that details whether the PDF/X-1a file has already been trapped.
• PDF/X-1a files contain extra operators that define the bleed and trim area.
• The MediaBox defines the size of the entire document
• Either the ArtBox or the 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).
• There is a flag which indicates that the PDF file is a PDF/X file and which also details what type of PDF/X file it is.
In May 2000, PDF/X was first put to use when Time Inc. processed a Bayer ad that was delivered as a PDF/X-1 file. PDF/X-1a is now an official ISO standard: ISO 15930-1.

There are 2 different PDF/X-1a flavors
• PDF/X-1a:2001 – such a file has to be a PDF 1.3 file.
• PDF/X-1a:2003 – such a file has to be a PDF 1.4 file but it should not contain any transparency and JBIG2 compression should not be used to compress images.
Both flavors share all of the restrictions that apply to PDF/X-1a. The 2003 version simply came along because some newer software applications no longer supported the older PDF 1.3 file format.

The PDF/X standard is a subset of PDF that focuses on "blind exchange" of prepress data. Each "flavor" of PDF/X is designed to address the needs of different workflows or users.
• PDF/X-1a supports CMYK and Spot color. This is the common choice in the US, where most printers aren't color management aware.
• PDF/X-3 supports full color management based on ICC profiles and device independent color. It is the common choice in Europe, where the printers are more concerned about color fidelity.
Both of these are based on PDF 1.4, but without live transparency. In order to address modern PDF workflows where the need to keep transparency live is important for high fidelity output as well as other newer features of PDF (like Layers), PDF/X-4 was created. It is based on PDF/X-3 and full color management.

Which other PDF/X flavors exist?
Below are all the PDF/X flavors that are either actively used in the market or may become popular in the future.
• 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.
• An updated version of PDF/X-3 which adds among others support for transparency and spot colors.
• Derived from PDF/X-4, allows external images.

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