Open Prepress Interface
A workflow 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 server’s 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. 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 colours. 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.
OPI is useful for minimizing high-resolution-file travel on networks; their large file size can make traffic screech to a halt. And by utilizing only low-resolution viewfiles on workstations, processing speed is increased. The efficacy of OPI is contingent upon the use on the workstations of OPI-compatible software; many page layout programs are increasingly including support for OPI, although some OPI specifications for color separation haven’t been effectively nailed down yet. Although OPI is often compared to DCS, the latter is strictly a color separation protocol, while the former is more of a workflow protocol.