In conventional 'every-page-the-same' printing, it might not matter too much if it takes 15 or even 30 minutes for the RIP to process a job before the press starts to roll, if it's then going to churn out hundreds or thousands of copies an hour. But in variable data printing (VDP), which is increasingly the physical aspect of many cross-media campaigns, a delay like that before each page can print represents a huge loss of productivity.
There are several factors in the VDP job creation process that can affect overall throughput. These range from from the ease of use of the authoring software to the precise way in which a job is constructed, particularly where high resolution images and live transparency effects are involved, such as superimposing variable text on a photographic image, for example. All of the guidelines and good practice that relate to the construction of static print also apply to VDP, but more so, because the delays from processing unnecessarily high resolution images or converting from RGB or spot colour to CMYK are a much bigger issue if they have to be repeated for every single impression.
The choice of VDP 'language' to pass the job on to the DFE/RIP may limit the scope for error; the older formats, which tend to be vendor-specific, are generally less flexible, so while restricting design freedom they may offer more reliable printing, especially where only features explicitly supported in the RIP hardware can be used. More recent 'open' formats such as PPML, which supports a degree of live transparency effects, and PDF/VT, which enables anything that can be done in static print to also be done in a variable context, present both greater design freedom and potentially greater productivity issues.
Beyond optimising VDP jobs for printability there are several attributes of the DFE and its software that can also make a considerable difference to productivity. Support for the necessary VDP file formats is the first and most obvious, but the usability of the software for job setup and control is also important. Most digital print shops run a mix of static and variable data print, so having tools that work in the same way for both will minimise the need for additional operator training and reduce the likelihood of error. Tools that permit automated workflow creation and sharing also help with this, while easy access to key VDP job information such as the number of database records used, how many pages there are per record and the total number of pages to print aids job identification and troubleshooting.
Pre-flighting is essential. Most VDP-creating software ensures that all the necessary resources are included in the print file, but processing large files can take a long time and it may not become apparent that there is a problem until printing begins. Pre-flighting tools should be able to check VDP output files for common errors such as incorrect image resolution, RGB or spot colours, hairlines and missing fonts.
Linking to external resources, such as graphics and images that are used repeatedly and which therefore do not need to be included in every print file, is a feature of 'thin' VDP formats such as VPS, PPML and PDF/VT2. The DFE will need to know where these files are and will ideally support local, remote and 'hot folder' locations.
Imposition is a critical process, especially when variable length products are being printed, and explicit support for subsequent finishing processes such as trimming, folding and binding, in whatever order they need to occur, is essential. Thumbnail-based previews are a useful visual aid to job identification and checking. The ability to define a record length in terms of number of pages is also valuable, as it enables jobs supplied as standard multi-page PDF files to be handled using VDP-specific tools.
An ability to preview individual rasterised pages, sets of records or imposed sheets also enables further visual inspection for errors, though VDP jobs supplied in PDF or PDF/VT can be soft-proofed (albeit in pre-rasterised form) using any PDF viewer.
Troubleshooting printer issues such as paper jams or finishing problems can also be streamlined if the DFE adds job header information for sheet number, record set and individual record ID. With this information, only the sheets that were spoiled need be reprinted, getting production back on track as quickly as possible, with minimal wastage of time and materials.
Caching text, graphic and image items that are used repeatedly is key to VDP printing performance, so that only the different parts of each new page have to be processed. It's useful therefore to be able to inspect cached items, both as a measure of how well optimised a job is and for re-use in other jobs. The internal architecture of the RIP/DFE also has an effect on productivity - advanced designs are able to start printing the first records while the last ones in the file are still being processed.
If you're planning to move into VDP to broaden your service portfolio then ensuring that you have the right front-end to drive your digital press productively is an essential step; checking through these questions should help you do that.
This is one of a series of articles based on The ABCs of VDP, a free e-book from EFI that explains the benefits of variable data printing (VDP) and describes with examples how print service providers can produce, promote and sell VDP services to their customers, expanding their business portfolio and increasing profit margins.