Page 196 - Graphic Design and Print Production Fundamentals

184 Chapter 6. Imaging
multiple RIPs, and within those RIPs they can utilize the multi-threading and processing power of
modern computer hardware and operating systems to process many pages or channels simultaneously.
PostScript has been the defacto PDL in digital printing for many years but with the development of the
PDF/X print standards and the subsequent release of the Adobe PDF Print Engine (APPE), a native PDF
RIP, many DFEs now include both PostScript and APPE as their available RIP engines.

ICC-based colour management workflow may be part of the RIP process or can be an independent
component of the DFE. Different elements within a print file get processed through their respective
channels in the colour management system. Common channels include CMYK, RGB, black, and
named colours. The idea is to convert all colour elements into the colour gamut of the print engine’s
colorants/paper combination. The conversion process can be complicated, but the basic concept is device
dependent source colour spaces (CMYK, RGB, etc.) are converted to a device independent colour space,
referred to the profile conversion space (PSC), then from the PSC to the output gamut defined in the
output ICC profile. The idea is to take the source ‘recipe’ and define the visual appearance of it first.
That is why it needs to convert to device independent colour space, which defines the visual appearance
of colour. Once the visual appearance is defined, the ‘recipe’ for the specific output can be calculated.

Systems that support named or spot colour rendering follow a similar process. The named colour is
located in a look up table. The name must match perfectly, including punctuation, spaces, and case. Each
named colour is defined in a device independent colour space, typically Lab. There is no calculation in
this step. The last step is the same; Lab values are then converted via the output profile.

There is one more calculation applied before passing the information through to the printer.
Electrophotography is affected by rapid changes in humidity and temperature. The electrophotographic
process relies on components that do become less effective over time and use. These factors all affect
the colour output. Calibration should be performed on a regular basis to compensate for these variables.
Calibration is a process of creating a correction curve to maintain consistent and repeatable print output.
This correction curve is applied right after the conversion to output profile, ensuring output is consistent
with what was defined in the output profile itself.

In order to maintain all these aspects of the DFE, an intuitive and user-friendly interface is critical. The
user interface includes many components. Here is where you would configure the DFE, find the status
of the print device and consumables, view and process jobs and job queues, and examine and export
job histories and logs. Many WYSIWYG tools are accessed via the user interface, such as those for
workflow, imposition, complex job composition, paper libraries, spot colour refinement, the launching
of external tools, and even interfaces into other systems such as web2print. DFEs are becoming more
powerful and perform more than just the traditional RIP functions. As the digital print industry continues
to evolve, DFEs will be called on to perform more duties and functions. User interfaces will need to
evolve as well to maintain usability and stay intuitive.