PDF/X is an umbrella term for several ISO standards that define a subset of the PDFCMYK or spot colors. PDF/X-2 and PDF/X-3 accept calibrated RGB and CIELAB colors, while retaining most of the other restrictions of PDF/X-1a. PDF (Portable Document Format) is a file format that has captured all the elements of a printed document standard. The purpose of PDF/X is to facilitate graphics exchange, and it therefore has a series of printing related requirements, which do not apply to standard PDF files. For example, in PDF/X-1a all fonts need to be embedded and all images need to be as an electronic image that you can view, navigate, print, or forward to someone else. The PDF/X standard was developed by the American National Standards Institute's (ANSI) Committee for Graphic Arts Technologies Standards (CGATS) at the request of newspaper publishers and advertisers. PDF/X is defined as a subset or a standardized version of PDF, specified to create more consistent and predictable files than using just PDF. It aims to reduce problems with PDF files that cause printing errors, unreliable proofs and corrupt files. By using the PDF/X standard, there is reduced operator intervention, fewer errors, reduced costs, time saving and improved color matching. It has more tightly defined variables than a PDF file can have. Rather than a printer specifying a set of Distiller or PDF settings to each client (worked out by trial and error), they can request that each client use PDF/X. In fact, a client can use this one setting for all their printers, a good example being an advertising agency, which would be able to use PDF/X for all adverts being sent to their magazines. PDF/X overcomes the problem that PDF can be used in many more ways than just pre-press. They can include comments and annotations, for example, and they may be made with RGB colors, or perhaps without embedded fonts. PDF/X format was created to facilitate “blind exchange” to minimise errors and speed up the production process. There are a number of versions of PDF/X standards published as ISO 15930:
PDF/X-1a is basically a PDF file with certain things disallowed. It addresses blind exchanges where all files should be delivered in CMYK (and/or spot colors), with no RGB or colormanaged data.
PDF/X-1a restricts the content in a PDF document that does not directly serve the purpose of high-quality print production output, such as annotations, Java Actions, and embedded multimedia.
PDF/X-1a eliminates common errors in file preparation, such as font mismanagement, incorrect color space, images which are missing and overprint/trap issues sending your document as a PDF/X-1a file will guarantee that these errors do not occur because for a file to be confirmed as complying to the PDF/X-1a standard: All fonts and images must be embedded All elements must be encoded as CMYK or spot. The file must be identified as trapped or not trapped
Closely related to PDF/X-1a but isn’t restricted to CMYK and spot colors. This standard supports Lab and RGB color and ICC color profiles. Where PDF/X-1a is suited for color managed workflow and restricted for this purpose, the PDF/X-3 format is more flexible and open. This requires good communication between designer and vendors to make sure problems don't arise. PDF/X-3:2002 is based on PDF level 1.3 and PDF/X-3:2003 is based on PDF level 1.4. PDF/X3:2002 is currently the recommended level when using this type of PDF/X.
Still in development, this is a more flexible format than both PDF/X-1 and PDF/X-3. It is not limited to CMYK, it supports the Lab color space and ICC color management as well as OPI workflows, and it does not require that fonts be embedded. PDF/X-2 is designed to address exchanges where there is more discussion between the supplier and receiver of the file. NOTE: Each succeeding implementation of the PDF/X format allows greater control for the modification of the file which is only of a benefit if the vendor has the knowledge to implement additional changes from the designer. Updates to PDF versions are not always embraced readily within the design and publishing industries for compatibility purposes. PDF/X-1a:2001 is the most common format, which will be the focus of this module and will be referred to as PDF/X-1a. Examples are shown using Adobe CS2 and Acrobat Professional 7.0. Earlier versions may show different menus, however, the principles are the same.
PDF/X is formalized in ISO Standard 15929 and 15930:
- ISO 15929 (which has been withdrawn in March 2008 and no longer is an official standard) specifies the guidelines and principles for the development of PDF/X standards.
- ISO 15930 defines the specific implementations.
- ISO 15930-1: PDF/X-1a:2001, Blind exchange in CMYK + Spot Colors, based on PDF 1.3
- IS O 15930-2: PDF/X-2, is not available online.ISO 15930-3: PDF/X-3:2002, Allows CMYK, Spot, Calibrated (managed) RGB, CIELAB, with ICC Profile, based on PDF 1.3.ISO 15930-4: PDF/X-1a:2003, revision of PDF/X-1a:2001 based on PDF 1.4ISO 15930-5: PDF/X-2:2003, An extension of PDF/X-3 which allows for OPI-like (external linked) data to be includedISO 15930-6: PDF/X-3:2003, revision of PDF/X-3:2002 based on PDF 1.4ISO 15930-7: PDF/X-4:2008, Colour-managed, CM
- YK, gray, RGB or spot colour data are supported, as are PDF transparency and optional content. It is designated as PDF/X-4p in case a required ICC profile is externally supplied.