Introduction to the PDF eXchange (PDF/X)
The third alternative when sending a digital document is send PDF ?les. This kind of workflow was expected to simplify the process a great deal. Unfortunately, the high expectations for PDF in this context haven’t been entirely ful?lled. Adobe wrote the PDF data format for use in a wide array of applications, not only for paper-based print production. PDF files can contain audio- and video-clips, annotations, animations, and so on. Such a PDP ?le is of course unlikely to be welcome into a print production workflow. Since 2001, there has been an ISO-standard for "prontable" PDFs, called PDF/X. This is a subset of Adobe PDF version 1.3, and excludes all parts of the PDP format that are not relevant for print applications.
Over time, at least three sanctioned versions of PDF/X have been introduced. The oldest are PDP/X-1 and PDF/X-3. And then there is the not yet ISO certi?ed PDF/X-2. PDF/X-1, including the latest version PDF/X-la, is the strictest since it requires high resolution colour separated ?les and does not allow OPI calls or DCS-?les. PDF/X-2 is supposed to be more tolerant and it accepts OPI calls and colour management with ICC pro?les. It is often stated that the PDF/X-1a de?nition doesn’t allow spot colours, but this is not correct - it does.
However, it’s only PDF/X-3 and PDF/X-2 that allow RGB and CIELab encoded images, coupled with the appropriate ICC profiles. While PDF/X has made it easier to specify how a PDF file should be constructed to be printable, the standard still doesn't specify such things as the minimum resolution required. To make up for this, the term PDF/X Plus has come up, indicating that the user or receiver has to provide some additional information about the printing conditions.
The Ghent PDF Workgroup, an Enfocus-initiated association of 12 industry associations from seven countries has defined nine PDF speci?cations to complement the PDP/ X standard with business sector- speci?c settings. Speci?cations have been published for ad delivery (magazine and newspaper ads), sheet fed and web printing; specifications for packaging are under development. In some cases there are separate speci?cations for CMYK-only and spot colour printing. Some speci?cations allow low resolution images while others only accept high resolution.
As much as we had hoped that PDF would end the struggle in electronic document delivery, there is still some way to go. Like it or not, one still has to preflight files before sending them off and PDF/X is fast becoming the most popular means of doing this.
