A direct imaging press is very similar to a conventional offset press except that the image carrier, or plate, is imaged directly on the press with built-in laser exposure units. The laser records the image onto the plate according to instructions it receives via digital files stored on a computer. The print quality is excellent with direct imaging presses because the actual process of printing is still based on conventional offset technology.

An Example of a Laser Unit for Direct Imaging of Plates

One of the primary advantages that a direct imaging press has over an offset press (without direct imaging capabilities) is that the preparation time per job is greatly reduced. 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. Many of the other makeready settings of the DI press, such as ink flow and cleanup, are accomplished as well, using the digital information stored for each project.

Unlike a true digital press, which can vary the image on every sheet printed during a single press run (variable data printing); the image cannot be changed on a direct imaging press while the press is running. Some DI presses can be used to print different versions of a document during a single press run, but the press must pause while a new plate is imaged for each different version. For example, on a five-color DI press, four print units can be used to print the full-color static portions of a document while the fifth print unit can be used to print the different versions of text that are required. When the printing of one version of the document is complete, the press pauses and the plate on the fifth print unit is imaged for the next version of the document. 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 more efficient process than conventional offset printing in which a separate base run is printed and then the sheets are sent back through the press (sheet-fed press) at a later time to print the different versions of text, or when using a roll-fed press, having to do manual plate changes for every version of the document and reregistering the plate so that the text lines up properly with the other printed elements.

The majority of direct imaging presses are capable of producing a minimum resolution of 1270 dpi, which is suitable for producing nearly 90% of all offset print jobs. There are a number of DI presses that are capable of much higher resolutions, which means that these higher resolution DI presses are suitable for printing almost any application that can be printed on a conventional offset press.

DI presses are very profitable in the 500 to 10,000 impression market. The cost per page in that quantity bracket is often much lower than most other comparable technologies, such as CTP (Computer To Plate) for offset printing and conventional offset printing with no CTP or direct imaging. Direct imaging presses are a good choice for organizations that want the quality of offset printing with the advantages of a digital workflow.