Direct imaging technology provides for the direct transfer of the image from
digital files to the image carrier (plate) of the press. A direct imaging press
is basically a conventional offset press except that the image carrier (plate)
is imaged directly on the press with built-in laser exposure units. Many of
the press settings, such as plate registration, ink flow, and cleanup are adjusted
with digital information as well. Unlike a true digital press, which can vary
the image on every printed sheet, the image cannot be varied during a press
run on a direct imaging press.
The advantage that direct imaging presses have over offset presses (without
direct imaging capabilities) is that the preparation time per job is greatly
decreased. Many of the manual steps of conventional prepress and presswork are
eliminated, such as producing films, preparing the films for platemaking, creating
plates, and mounting and registering plates on the press. The print quality
is excellent with direct imaging presses because the print process is still
based on offset technology.
Although direct imaging presses cannot accomplish variable information printing
like true digital presses, some DI presses are able to print different versions
of a document during a single press run. For example, a five-color press can
use four print units for printing the full color static portions of a document
and use the fifth unit to print the different versions of text that are needed.
The plate on the fifth print unit is reimaged at the appropriate intervals for
each version that is required. After the plate is imaged, the printing proceeds
until it is time for the next plate to be imaged, and so on. The result is a
document that has the same layout and color elements, but differences in the
text for each version. This is a much better process compared to conventional
printing in which a separate base run is printed and then the sheets are run
back through the press at a later time to print the different versions of text
(sheet-fed press), or when using a roll-fed press, having to print the static
portions along with the text for every version.
The majority of direct imaging presses are capable of a minimum resolution
of 1270 dpi which is suitable for producing nearly 90% of all print jobs. Many
DI presses offering much higher resolutions than 1270 dpi so there are few applications
that are not suited for DI presses.
DI presses are very profitable in the 500 to 10,000 impression market. They
have a lower cost per page in that quantity bracket than most other technologies
that are comparable, such as CTP (Computer To Plate) and conventional offset
printing. Direct imaging presses are a good choice for those who want the quality
of offset printing with the advantages of a digital workflow.