T he next big step in prepress will be PDF/X-4, which allows transparency and layers. But what about the support of PDF/X-4 by RIP vendors? The Flemish Innovation Center for Graphic Communication (VIGC) has carried out its first PDF/X-4 audit and is pleased to report that seven systems were awarded its 'PDF/X-4 Audit: Passed' label. The audit involved the first large PDF/X-4 RIP test in the world, and following the results a number of vendors have improved their products.
"PDF/X-4 has many advantages, as it allows transparency and layers, presenting a variety of opportunities for different markets," says Eddy Hagen, general manager at VIGC. "But with that transparency, you open the door to a much more complex world than flattened PDFs.
“At VIGC, we wanted to thoroughly assess PDF/X-4-capable RIPs to see whether they can render those PDFs correctly. Rendering a file incorrectly can result in a reprint, which means extra costs."
Didier Haazen, senior innovation consultant at VIGC and PDF expert continues: "Transparency is particularly challenging and can be a real Pandora’s Box. For example, not everyone is familiar with how to correctly use a 'transparency blending space' in Adobe InDesign. And if you’re going to mix different modes, things become very complex – you can end up with different results when rendered on different systems."
Test set: Altona, new GWG patches, VIGC color test files
The test set used by VIGC wasn’t made up of average documents. On the one hand, they used Version 2 of the Altona Test Suite, which has all theoretical combinations possible. However, a part of those are hand-coded, meaning they can't be produced with known design and layout tools.
On the other hand, a number of new patches from the Ghent Output Suite (GWG) were used – a large number of those were developed by VIGC, which is heavily involved with GWG.
And to test the possibilities of color conversions, VIGC also created additional test files.
An important learning exercise
Haazen explains the success of the tests: "The tests proved very useful to the developers involved. On many occasions we found some minor errors, bugs that were fixed either on the spot or in a few days’ time. During the tests, we often had a direct line with the software developers, who were very happy with the thoroughness of the tests."
Lieven Plettinck, Director Software Development at Esko, confirms: "It was absolutely a useful exercise, particularly regarding the test patches created with real applications. Even the synthetic patches taught us something – notably, where there could be ‘pain points’ in the software, which could be triggered by new software tools."
The problem areas – transparency blending spaces and black point compensation
The main conclusion of the VIGC PDF/X-4 Audit highlights the complexity of transparency. During the tests, there seemed to be differences in interpretation of some very specific cases, which can be traced back to different interpretations of that small part of the PDF specification itself.
"When we saw this, we immediately contacted ECI, the makers of the Altona Test Suite, to get some more information about a number of their patches," Haazen explains. "They confirmed our observation and explained that the different parties involved are working very hard to clarify the PDF specifications. This, of course, takes some time: the PDF file format has become an ISO standard, and changing it means passing several formal stages. So, while the official version of a solution may take some time, we expect a practical solution soon."
In addition to differences in interpretation between vendors, there can also be a difference within the products of one vendor. The most notable is the rendering in Adobe Acrobat: this changes when the 'output preview' is activated.
Although not part of the PDF/X-4 specifications, there were also elements included to test black point compensation (BPC). BPC is a popular functionality in the Adobe Creative Suite, but the question is whether RIPs also support this function. During the test, it quickly became clear that this is not the case – which means it can lead to differences, particularly if the color conversion is done in the RIP itself.
Therefore, it’s important to establish whether BPC is important in a workflow. If so, it’s necessary to check if a vendor or workflow software supports it.
GWG specifications – the safe way
"Despite these issues, PDF/X-4 certainly is a good and safe solution, as long as the PDF is created the right way and some rules are followed,” continues Haazen. “And this is where the GWG plays an important role, and it has for some time been working on new PDF/X-4 based specifications."
“Within the GWG, we’ve already carried out many tests to get to a 'safe' workflow. The VIGC PDF/X-4 Audit confirms that creating a PDF in any other way can lead to strange behavior. When the VIGC test results were shown during a GWG meeting, there was much interest from developers and users."
The new GWG specifications will likely be launched by the end of the year.
PDF/X-4 Audit – Passed and Perfect
The VIGC awards a label to the systems that have passed its tests. The organization makes a distinction between a ‘perfect’ accreditation – where everything was rendered as expected – and 'passed'. The difference between the two is mainly a part of the Altona Test Suite, i.e. that part where there’s disagreement about the correct rendering.
Also, some patches of the VIGC test files weren’t considered 'wrong' – for example, when minimal color differences occurred.
Taking this very realistic approach into account, the following systems received the VIGC PDF/X-4 Audit: Passed label:
- EFI - XF v4.5.5
- Esko - Esko Suite 12
- FujiFilm - XMF v22.214.171.124
- GMG - ColorProof v126.96.36.199
- Heidelberg - Prinect 2011 SR1
- Kodak - Prinergy 188.8.131.52
- Xeikon - X800 Digital Frontend
The VIGC has drafted an extensive test report featuring the results of those systems that passed the audit, as well as the issues encountered with other systems (note: these systems haven’t been named.). The full report can be purchased from the VIGC.