PDF/X-4 is the next big step in prepress, but until VIGC (Vlaams Instituut voor Grafische Communicatie — Flemish Innovation Center for Graphic Communication) actually set up a test for looking into the support of RIP vendors, nobody knew if there were any vendors who fully complied with this standard.
PDF/X-4 needs the following parameters to be complied with:
- The use of transparency is allowed
- All colour data can be greyscale, CMYK, named spot colours, RGB, Lab or ICC-profile based
- Image data can be 8-bit or 16-bit
- The use of layers is allowed.
In PDF/X-4 layers are not the regular PDF layers (so-called OCG or Optional Content Groups) but more sophisticated OCCD layers (these combine multiple OCGs in a group).
PDF/X-4 obviously has restrictions too:
- 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
- Only a limited number of compression algorithms are supported, including JPEG 2000
- Encryption cannot be used
- Transfer curves cannot be used.
Finally, some information needs to be added to a PDF/X-4 file:
- 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
- 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 colour profile or an output condition identifier, which is simply a text description of the intended print specifications (e.g. FOGRA27).
The problems with RIPs supporting PDF/X-4 will be in the area of the parameters and what the RIP does with the information added to the file. VIGC created a test to evaluate to which extend the most common RIPs support PDF/X-4. Their test used the Altona Test Suite, new Ghent Output Suite (GWG) patches, and VIGC colour test files.
VIGC used version 2 of the Altona Test Suite, which has all theoretical combinations possible. The problem areas would be transparency blending spaces and black point compensation. VIGC reports that during tests there seemed to be differences in interpretation of some very specific cases. These could be traced back to different interpretations to that part of the specification itself.
VIGC then decided to assign a label based on the distinction between all elements being rendered as expected (or rather: as supposed to), and render results where some elements were not as they were supposed to be (Perfect and Passed, respectively).
VIGC points out that the difference between the two us mainly attributable to the Altona Test Suite, where there is a disagreement about what makes up for a correct rendition of elements. Also, when minimal colour differences occurred in the colour patches of VIGC's own test files, these weren't considered to be wrong.
Based on these criteria, tests and parameters, there were a whole bunch of products that merit the Passed label.
Among these were: EFI XF v4.5.5, Esko Suite 12, FujiFilm XMF v220.127.116.11,GMG ColorProof v18.104.22.168, Heidelberg Prinect 2011 SR1, Kodak Prinergy 22.214.171.124 and Xeikon X800 Digital Fronted.
There was only one that merits the Perfect label: EFI Fiery FS100 Pro.