PDF/X-4.0 is an ISO standard (see: www.iso.org). The first version was released in 2008 as ISO 15930-7:2008. An updated version ISO 15930-7:2010 was released in 2010.
The PDF/X-4 standard brought with it transparency, OpenType fonts, optional content (layers), page sizes beyond 5 by 5 meters, JPEG2000 compression and more. To use this new standard optimally in WebCenter, a few changes are required to the default settings. These changes will result in the best support WebCenter and Automation Engine can give for PDF/X-4.0 and pass the Altona and GWG tests for PDF/X-4.0.
PDF/X-4 compatibility depends on the settings for Color Management in the Normalize step that converts the incoming PDF/X-4 file to an Esko Normalized PDF, capable of being viewed in the WebCenter Viewer. Follow these steps to setup the Ticket correctly:
- Use Automation Engine Pilot to connect to your WebCenter OBGE.
- Open the Tickets View.
- Open the Ticket with the Normalize PostScript / PDF/ Illustrator 8.0 File Task Type and
- Change the following settings in the Color Management tab of the Ticket:
In the Destination Color Space section, enable Use PDF Output Intent if available. A PDF/X-4 file always contains a CMYK ICC profile that defines the CMYK color space of the intended output device. This profile must be used to convert all CIE based objects in the PDF (Lab, RGB with attached ICC profile, CMYK and Gray with attached ICC profile) to CMYK. For PDF/X-4 files, the destination profile selected in the drop down list does not matter as there is always an output intent profile for PDF/X-4 files.
In the RGB section, set Objects with RGB Profile Tags to Convert using profile tag. RGB objects having an attached ICC profile should to be converted from RGB to CMYK using the RGB ICC profile and the CMYK output intent profile.
PDF/X-4 forbids the use of RGB objects without attached ICC profile (DeviceRGB).
In the CMYK and Gray section, both CMYK and Gray objects with Profile Tags should be set to Convert, preserve appearances. CMYK objects having an attached ICC profile have to be converted from source CMYK to output intent CMYK using the attached CMYK ICC profile and the CMYK output intent profile. Gray objects having an attached ICC profile have to be converted from source Gray to output intent CMYK using the attached CMYK Gray profile and the CMYK output intent profile.
PDF/X-4 forbids the use of CMYK objects with an attached ICC profile that is identical to the output intent profile to avoid unwanted color conversions that can negatively impact separations. PDF/X-4 allows use of untagged gray objects (DeviceGray). In this case gray is mapped on the black channel of the CMYK output space.
- Save the Ticket under the name
Interpreting the Results
The result of the test suites show how good various Tickets and Programs perform for PDF/X-4 support. They do not talk about color accurateness of the Viewer. When we compare color, we only discuss how the test patch compares to the reference image. Thus, if the result is positive this means the technical rendering is correct. Color is just a means to test the rendering of the technical issues arising when using transparency, layers and non visible content.
Esko does not claim that the WebCenter Viewer is color accurate when comparing print to screen.
GWG Test Suite
The GWG test suite does not bring any surprises as this test suite tests the technical capabilities without color conversion. As the biggest difference in both Tickets lies in the color profile handling we do not see any differences between the old and the new Ticket. On a technical level, we do sometimes see some artifacts but these do not differ from the original Ticket and can be ignored in the GWG Test suite. The WebCenter Viewer thus passes the test suite.
Altona Test Suite
Here you can check the result patch by patch of the Altona Test Suite. The result of the Altona Test Suite shows that the Viewer is PDF/4-x ready on a technical level. We also see improvements in color accurateness because the OnDemand Ticket is respecting the original ICC tag. Although some restrictions apply concerning the RGB shadings.
For more information, see:
Known Limitations and Potential Problems
PDF/X-4 allows usage of objects that require color conversions in a PDF (e.g.: Lab, RGB with ICC profile, CMYK with an ICC profile other than the output intent profile, Gray with ICC profile, etc.). PDF/X-4 also stipulates clear rules on how these objects should be converted from their color space to the output intent color space to obtain predictable results. However there are a number of potential problems.
Color conversion based on ICC profiles can result in output separations that generate bad print quality. Some examples:
- An object defined in a Gray color space with attached ICC profile will be converted to CMYK using the output intent profile. The output separations will most likely contain C, M, Y and K values. For small text on print processes with imprecise register this is a problem.
- Conversions for objects defined in Lab, RGB or CMYK can result in small dots that are difficult to print in flexo.
- Conversion of an object in CMYK other than the output intent can result in CMYK values with different black generation and a TAC (total area coverage) that exceeds the limit for the intended printing process. The user should consider if this is a problem in his specific workflow and if so either avoid the usage of objects requiring color conversions in incoming file or insert steps in the workflow to correct such situations.
- A method called Black Point Compensation was introduced in Adobe® products to improve color conversions. (See http://www.color.org/AdobeBPC.pdf). Applying this method can give very different results especially for RGB to CMYK conversions. Unfortunately this method is not part of the PDF or the PDF/X-4 specification. Some vendors have implemented it, others not. This breaks the intended predictability of PDF/X-4 workflows. Note: In Suite 12, Black Point Compensation was introduced in such a way that it is compatible with Adobe® applications. The user should verify that systems in his workflow use Black Point Compensation in a consistent way.
- In some applications such as Adobe® Indesign®, it is possible to specify that transparency blending has to be done in RGB instead of CMYK even if the file is intended for print. The PDF/X-4 specification allows this, however tests of the VIGC and others have revealed that implementation of this feature is not implemented or implemented in different ways in the most popular applications available. To achieve predictable results, the user should avoid usage of blending color spaces other than DeviceCMYK in incoming files. Note: The Altona V2 testsuite contains patches with transparency blending spaces other than CMYK. Those patches give inconsistent results in the majority of the systems on the market.
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