Tuesday

Open Prepress Interface

protocol developed by Aldus Corporation used in electronic prepress to link desktop publishing systems and high-end CEPS. Essentially, high-resolution color images are stored on a central network server, to which all the workstations are connected. Low-resolution files are sent by the server to individual computers working on page layout. The low-res images are imported into the page (in a kind of FPO way), positioned, and comments sent back to the OPI server provide specific cropping, scaling, positioning, and color information about the image. The servers PostScript driver inserts the proper instructions into the PostScript code. When the page is ultimately output to an imagesetter connected to the network, the high-resolution image is swapped for the low-res one, and the indicated instructions as to cropping, etc., are executed.
The work with layout documents which include big graphic files (high resolution, big size) may become a test for someone’s patience due to the rate of the processing. The dealing with this kind of files, which need a lot of memory in the workflow, can be simplified with an Open Prepress Interface (OPI) System. Although the PCs and networks become constantly faster and powerful, OPI is used for the Prepress workflow in order to minimize the waiting period. It is in use for 10 years now, but only a few people know this application.

OPI- principle

If a graphic file is placed into a document, layout applications normally integrate the whole graphic file. If the graphic files are big, the processing of the document becomes very slow due to the quantity of the graphic data. The resources needed by the PC and the network (if used) are unnecessary; because low resolution graphic files are sufficient for the work on a monitor in order to create the layout or to judge the colors.

Because of this, OPI-programs create low-resolution graphic files with the same dimensions and place them into the layout document instead of the originals. The high-resolution files are integrated by an OPI-server just after the print job is started. The OPI-server finds the data by so called OPI-comments, which are included in the PostScript print file or in a PDF file. These OPI-comments describe, among other things, the memory needed, the sizes, and the position of the graphics in the layout document. Another aspect is the possibility to share the work of one project between the graphics and the layout, because the final graphics are embedded after the print job is started.

Therefore, the output files include only references to the original high-resolution graphic files in order to save resources of the PC and the network. The big advantage is that the resources which are needed of the computer for the layout document are moved from the PC to the server. This saves time and costs. If there is a powerful OPI-server, the print job is speeded up, too.

There are, among others, three popular OPI-server programs. All three programs are offered for different platforms:

EtherShare OPI from Helios

UNIX (Solaris, AIX, HP-UX, IRIX, Compaq UNIX)

LINUX

Windows 2000

Mac OS X

Color Central from Scenicsoft

Apple Mac OS

Windows NT 4 Server

Windows 2000

Full Press from Xinet

UNIX (Solaris, Solaris x86, IRIX)

Mac OS X

Windows NT 4

Windows 2000 Server

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