| Facilitating file exchange with PDF specifications |
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| Written by Enfocus Software | |
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The vast majority of print jobs are co-operative efforts involving several companies
Designers create the artwork; prepress companies often finalise the artwork technically; publishers collate input from several sources into one publication; and printers let their presses hum, producing the end product. Transferring the documents in a way that is both simple and technically reliable is a key challenge for the graphic arts industry. A number of file formats have become popular over the years: native file formats, PostScript, TIFF/IT and vendor- specific formats like the Scitex CT/LW. During this time the graphic arts community has learnt to live with, and work around, the limitations of the different file formats. The end result is that a sizeable chunk of the jobs supplied to a printer require intervention on the files before they can be printed. This puts a tremendous burden on the printer and the prepress department. More often than not the cost is borne by the printer, eating into profitability. PDF, conceived by Adobe in 1992, although perhaps not perfect, is a much more robust basis for file exchange in the graphic arts community. The strengths of PDF All-in-one A PDF file contains (or, to be precise, can be told to contain) all the components needed to visualise the file. Cross-platform PDF is conceived to look identical on any computer platform. Compact In general, a PDF file is significantly smaller than its equivalent in another file format (almost five times smaller). Elements in the file are compressed with a suitable algorithm depending on the type of element, and images can be resampled to an appropriate resolution. Easy to use and inexpensive All you need to create a PDF file is Adobe Acrobat Distiller. The product is sold as part of Adobe Acrobat and is presented as an office application for any PC user. As any application can generate PostScript, and PostScript can be distilled into PDF, PDF can be generated from every application. Structured The shape and attributes of every component are stored inside the file, including text, fonts, colours, Bézier curves, vectors and images. Shapes and attributes can be accessed and modified individually, without touching anything else in the file. As a result, last minute changes can be made to the document, using PDF editing tools. Public Adobe authors (and controls) the technical PDF specifications. The company publishes these specifications, making them accessible to anyone. As a result, any determined party can build tools around the PDF format and it also becomes possible to refer to these public specifications in official ISO standards, such as PDF/X. Unfortunately, the world of PDF is not perfect – PDF suffers from the weaknesses of its strengths. It is such a flexible format that you can use it to transmit a contract to your client for review, post flyers on the Web and transmit ads to a magazine publisher. The same product is used, the same actions are performed, however different settings should be used in each case. PDF makes it look so simple. Before the desktop publishing revolution, only experienced professionals were able to prepare documents fit for print. Today, the creation of print-ready files is accessible to the rest of us – newborn designers, often unaware of the technicalities of the process. It is therefore essential to check (or preflight) a PDF file against the appropriate requirements before sending it to the next station in the workflow. Other shortcomings of PDF are highly detailed technical ones, or concern limitations of the products used to create or consume PDF. Many of these issues can be detected during a detailed preflight scan of the file. But in general, of course, there is no automatic miracle cure. In those cases, a good editing tool – and a responsive support department – may jigger the work in order to complete the job. In summary, to help PDF become the perfect format for graphic arts, we need standardisation. Industry research in editing and quality control of PDF files has lead to the realisation that a number of important requirements are going unfulfilled by the PDF specifications. These needs all revolve around the same issue: PDF files have no ‘memory’. Performing a preflight operation leaves no trace in a traditional PDF. It is impossible to trace edits, to compare the file before and after the editing session, and to identify who has made those edits. This can cause finger-pointing and denial of responsibility when a print job ends up looking unrecognisable to the client. Technology has been developed to cater to these needs, so that a PDF file can be ‘self-aware’ – recording whether or not it was preflighted, the settings that were used and whether or not the file passed the test. A complete log of all edits performed to the file is recorded. Moreover, whenever a file is edited, the operator will be prompted to re-preflight the file before saving. Standardising PDF for print Not all PDF files are suited for print purposes. In order to be fit for print a PDF must comply with a set of more restrictive criteria. Several organisations have taken the initiative to define these criteria. The first organisations to set such specifications were large individual printers and publishers, who defined requirements and guidelines based on their own workflows. Later on, national industry associations started defining specifications for their respective industry segments. Over the last few years, two important international initiatives developed: PDF/X and the Ghent PDF Workgroup. PDF/X defines a common ground for PDF used in print workflows, while the Ghent PDF Workgroup aims at defining industry-segment-specific settings. Over the years, several associations have taken initiatives in setting specifications for PDF files. National associations in countries such as Australia, Finland, the UK and the US have set ‘local’ countrywide specifications. A number of organisations took the initiative to define a common ground for PDF used in print. A working group was created inside the Committee for Graphic Arts Technology Standards (CGATS), initiated by the American Digital Distribution of Advertising for Publications (DDAP) and the Newspaper Association of America (NAA), and involving several industry vendors and users. The resulting PDF/X specification (ISO 15930) is a true standard, similar to standards for camera film sensitivity (ISO 400) or quality management (ISO 9000). The objective of PDF/X is to allow ‘blind exchange’ of PDF files in a graphic arts workflow. PDF/X is designed to be sufficiently generic to cover all market segments of the print industry, from newspaper ad delivery to oversized poster printing. The Ghent PDF Workgroup The objective of the Ghent PDF Workgroup is to take PDF/X a step further, by developing more segmented and detailed specifications. It all started when Medibel+, a Belgian association representing the players in the ad delivery process, decided to set specifications for ads exchanged in the Belgian market. Roularta, Belgium’s largest publisher and magazine printer, was in charge of the project. It decided to hold a pragmatic bottom-up approach to the issue: what are the typical problems with PDF files received from designers, and which preflight product best detects those issues? After extensive testing, one product emerged that could identify 96 per cent of all concerns – far better than any alternative solution. So Medibel+ expressed its specifications based on this product (a set of preflight rules) and Adobe Acrobat Distiller job options. These specifications were distributed to the parties delivering ads, so they could check files before sending them out to the publishers. The approach was a success, dramatically reducing error rates of incoming files. Conclusion At first glance it may seem complex. However, implementing PDF specifications is really not that difficult. The Ghent PDF Workgroup and the various industry associations have made every attempt to keep things simple. All necessary information is available from their respective websites, providing ready-to-use tools and guidance. For further information on the Ghent PDF Workgroup please visit www.ghentpdfworkgroup.org |
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