Prepress Workflow Advancements Utilizing PDF/X-4 and the Adobe PDF Print Engine

摘要

Current prepress workflow processes have evolved significantly due to improvements to PostScript technologies; however, inherent limitations with PostScript still remain. Modern releases of Adobe's Portable Document Format (PDF) include features that are not supported in a PostScript environment, and consequently, native PDF prepress workflows and new PDF standards have been developed to take further advantage of advancements in PDF architecture.It wasn't until the release of ISO standard PDF/X-1a:2001 (ISO 15930-1) that the PDF/X standard gained uptake amongst application developers. Based on PDF 1.3, PDF/X-1a:2001 provided accuracy and predictability, while maintaining some degree of flexibility within the prepress workflow. However, as authoring software continues to grow in complexity, features have been added that are not easily supported in a PDF/X-la:2001 file or traditional PostScript RIPs, such as native vector transparency and ICC color managed workflows. The need to flatten transparency and convert to CMYK so early in the workflow limits flexibility and repurposing of the PDF file and can result in unpredictable errors in output. PDF/X-4:2008, which became an ISO standard (15930-7) in 2008, offers many features that can overcome the limitations inherent in PDF/X-1a:2001, specifically when integrated with a native PDF workflow, such as the Adobe PDF Print Engine launched by Adobe in 2006.Both the Adobe PDF Print Engine and the PDF/X-4:2008 standard are still in the early stages of their respective product life cycles, and mainstream adoption has not yet occurred; consequently, this research project was conducted to test the feasibility of using these combined technologies for existing large-scale production workflows, specifically magazine publishing.In this two-stage research project, the end usability of both PDF/X-la:2001 and PDF/X-4:2007 (draft) files was tested. It should be noted here that PDF/X-4:2007 is a draft specification of the ratified 2008 standard which was available as an Adobe PDF Preset in Creative Suite 3, hereafter referred to as PDF/X-4:2007. Custom test pages, as well as version 2 of the Ghent Output Suite, were used to contrast and compare output results created from running PDF/X-la:2001 and PDF/X-4:2007 files through workflows based on a Configurable PostScript Interpreter (CPSI) RIP and Adobe PDF Print Engine (APPE) RIP.In phase one of the research PDF/X-la:2001 and PDF/X-4:2007 files were created as a direct export from Adobe InDesign CS3 and were processed at three different magazine production facilities, all using a Kodak Prinergy 4.0 workflow system. The PDF/X-la:2001 files rendered differently for each of the three test teams, depending on the job processing parameters set within the RJP. None of the PDF/X-1a:2001 files output as was intended in the original files, regardless of whether the CPSI or APPE RIP was used. The PDF/X-4:2007 processed with the CPSI RIP also produced erratic and inconsistent results for all output teams. In contrast, the PDF/X-4:2007 files processed with the APPE RIP reproduced consistently for all teams, with the output matching the intended result in the file. The PDF/X-4:2007 files processed through the APPE showed a clear improvement in the reproducibility of vector-based transparent objects, especially when spot color objects were placed in transparent vignettes, and then mapped to process as part of the RIP workflow parameters.Phase two testing narrowed down the test parameters to focus on the discrepant results found in phase one. In particular, it was discovered that a PDF/X-la:2001 file would produce much different results based on where in the workflow Pantone colors were mapped to process. Further testing was done with regard to the effect of color mapping on transparent Pantone objects in the flattened PDF-X/1a:2001 files, as well as the effect of different overprint settings set within process template of the RIP. The findings in phase two confirmed that the application of color mapping at different stages of the workflow had significant affect on the outcome when PDF files are flattened prior to output but had little consequence for the non-flattened PDF/X-4:2007 files processed through an APPE RIP.Based on the results of both phases of testing, it was concluded that PDF/X-4:2007 files processed through the Adobe PDF Print Engine could offer measurable workflow improvements over flattened PDF/X-1a:2001 files processed using a conventional CPSI (PostScript) RIP, especially when vector transparency with spot color objects come into play. In addition, it was determined that the expanded color managed color spaces could be very useful for printers that are looking to implement a late binding color workflow to better take advantage of mixed output capabilities, such as traditional offset and digital print.