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The Digital Front End (DFE) is the brain of a digital production press. The majority of the processing required to prepare a job for the print engine itself is carried out within it. That processing can include automated imposition, trapping, color management, VDP processing and, of course interpreting and rendering, or RIPping.
In many cases the press controller, which talks directly to the marking engine in the press, is also a part of the DFE. In some light and medium volume production presses the DFE may be mounted within the press casing, but it’s usually found as a separate unit, either installed alongside the press, or in a separate, climate controlled, server room.
Digital Front End components
- An overall DFE control process
- Optional print file pre-processors. These could include image optimizers (e.g. red-eye reduction for photo-books) etc.
- One or more RIPs to render from the input file format (e.g. PDF) to a raster of each sheet to be output as a grid of pixels.
- Optional post-processors that act on the raster date after the RIP, e.g. reconstruction of final pages from page parts for variable data print jobs.
- One or more press controllers that deliver the raster data to the press to actually print it.
- Disk storage for incoming jobs and/or rasters produced by the RIP.
The software is often a collection of different products and technologies from several different suppliers. Usually some of those software components are built by the press vendor themselves; the overall control process and the architecture for data flow tends to fall into this category.
In some cases pre- and post-processors and/or raster deliver to the press can be hardware assisted to increase performance. Construction of the final page raster for printing when using a VDP optimization technology that makes use of external caching of page parts is a common case where hardware acceleration can provide significant benefit.
Terminology
The terms “Digital Press” and “Digital Front End” are used mainly by people from a graphic arts and conventional printing background. Those who have worked in a data center tend to talk about “printers” and “controller” instead. The terms are interchangeable, but we have used the graphic arts terms within this website.
DFEs almost always include one or more RIPs (raster image processors) that render from a page description language (PDL) such as PostScript, PDF or XPS to a raster: a pixel-based representation of the page suitable for delivery to the print heads of the press. Thus a RIP is a component of a DFE, the two are not synonymous.
The presses themselves can be sheet-fed (sometimes called cut-sheet) or roll-fed (sometimes called web-fed), and may use electrophotographic (EP, often called toner) or inkjet imaging technology. In general there are rather few differences in the RIP functionality required between these various types.
RIPping through data
Performance versus cost
The primary goal of a DFE is to provide rasterized page data to the press itself sufficiently rapidly to ensure that it can run continuously at rated speed.
Given an appropriate architecture it’s possible to achieve that goal for any press speed by increasing the power of the hardware and the number of RIPs etc. That raises a second requirement: that the press can be driven at speed without requiring an excessively high bill of materials for the DFE.
It is important to design a DFE such that it provides the data rate required at as low a cost as possible. A key factor in achieving this goal is to choose the most efficient components available, including the RIPs. It is an area in which the Harlequin RIP has a significant track record.
Process locations within a DFE
- Interpreting/rendering – 2
- Color management – 2
- Imposition – 1, 2 or 3
- Screening – 2 or 3
- Trapping – 2 or 3
- Font handling – 2
- Variable data
- PPML etc – 1 or 3
- PDF without h/w assist – 2
- PDF with h/w assist– 2 and 3
- PDF/VT – 1 and 3 or 1,2 and 3.
RIP workload
- The press speed (Letter/A4 impressions per minute for a cut-sheet press, media speed and width for a roll-fed one)
- Printing resolution (doubling the resolution in both dimensions quadruples the data rate required)
- The number of colorants used on the press (from mono, through highlight color, to full-color (which usually means CMYK), to hifi and photoink color sets. In some cases full-color presses may also use spot colors, such as MICR)
- What proportion of the jobs being processed can take advantage of specific optimizations that accelerate variable data print jobs
- Whether output is screened in the RIP or post-RIP (in efficient RIP solutions screened data can be produced at about the same page rate as contone data, but the resulting data is smaller, making it faster to store or transmit. On the other hand, screened data is not as amenable to variable data optimization techniques using caching outside of the RIP)
- Whether technology is available to enable external caching of page elements for variable data print jobs
- How graphically complex typical jobs at that print site are (including how much live PDF transparency is used, how much image coverage there is, and the input resolution of those images, etc.)
- What the shift pattern at the print company is like (especially the balance between shifts submitting work to the press and shifts where the press is running, but no new work is submitted).
Categories of digital production print
In addition, different print sites have different expectations as to the proportion of jobs that should achieve engine speed while printing. This tends to vary with the category of press, usually based on the recommended duty cycle of the press, rather than its rated speed. The higher the duty cycle the higher the price of the press, the more strategic an investment it is for the print company, and the higher the expectation of delivery.
The computers that make up a DFE can vary from a single workstation-class computer to a rack full of server-class units depending on the performance requirements for that press in that site.
| Category | Duty cycle (pages per month) | Common printing technology | Typical RIP configuration |
|---|---|---|---|
| Light production | 100k – 300k | EP, sheet-fed | Single RIP process on a single computer (single or multi-threaded) |
| Medium production | 300k – 1M | EP, sheet-fed (with just a few roll-fed) | Single, multi-threaded, RIP process on a single computer |
| High volume production | 1M – 15M | Mainly EP, sheet-fed, but some IJ and roll-fed | Multiple multi-threaded RIP processes on one or more computers |
| Very high-volume production | 15M – 60M | IJ, roll-fed | Multiple multi-threaded RIP processes on multiple computers |
| Ultra high volume production | 60M+ |
