Pre-flight

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Pre-flighting is a term used in the printing industry to describe the process of confirming that the digital files required for the printing process are all present, valid, correctly formatted, and of the desired type. The term originates from the pre-flight checklists used by pilots.

[edit] Background

In a common digital pre-press workflow, computer files provided by clients will be translated from an application-specific format such as Adobe InDesign or Quark XPress to a format that the raster image processor (RIP) can interpret. These intermediate formats are commonly called page description languages (two common PDLs are Adobe PostScript and Hewlett-Packard PCL). The RIP prepares the final raster image that will be printed directly (as in desktop inkjet or laser printing), set to photographic film or paper (using an imagesetter), or transferred direct-to-plate.

Depending on the hardware and software components and configurations, RIPs have unique problems rasterizing the image data contained in a PDL file. If there is a failure in rasterizing the image, it can be costly, as imagesetters, direct-to-plate systems, and high-end inkjet printers can consume expensive supplies, can require extensive amounts of time to process complex image data, and require skilled labor to operate.

[edit] The pre-flight process

The process of pre-flighting a print job helps to reduce the likelihood of failure of rasterization or output by examining the files that are to be printed. Modern page layout software applications, which allow users to combine images, graphics, and text from a variety of formats, now automate this process. The pre-flight process checks for:

  • linked files are accessible to the application
  • fonts are accessible to the system
  • fonts are not corrupt
  • fonts are in a compatible format
  • image files are of formats that the application can process
  • image files are of the correct color format (some RIPs have problems processing RGB images, for example)
  • required color profiles are included
  • image files are not corrupt
  • confirm that document size, margins, bleeds, marks and page information all fit within the constraints of the output device
  • confirm that the correct colour separations or ink plates are being output

Other, more advanced features might also include:

  • removing data that will not print, such as non-printing objects, hidden objects, objects outside the printable area and objects on layers below
  • flattening transparent objects into a single opaque object
  • converting fonts to paths
  • gathering files in one location
  • compressing files into an archive format
  • uploading files to a service provider
  • copying files to disc

The specifics of what is checked for are determined by the pre-flight application, the subject file format, and the selected output device.

A purpose-built software application is not required to pre-flight a file, although several commercial applications are available. Small shops may use an inexpensive laser printer to test whether or not their file will print. The conversion to Portable Document Format (PDF) can reveal problems, and as such qualifies it as a pre-flight process.

[edit] History

Early pre-flight methods were largely manual, and typically relied on checklists that operators would use on every output job. As applications, PDLs, RIPs, and output devices evolved, the process became more complex. Software plug-ins and stand-alone applications that supported the major desktop publishing applications were then developed to meet that need, along with proprietary tools made by hardware manufacturers and commercial printers and service bureaus. The developers of the major applications then began to incorporate functionality in their applications, leveraging their knowledge of their own file formats.

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