A Little History
OPI is an extension to the PostScript language that minimizes file size by permitting an application or user to insert a set of comments describing the location, size, and cropping of an image in a page layout, rather than the image itself. In addition to spatial issues, OPI comments can also describe the bright-ness and contrast of an image.
The specification was initially developed by the Aldus Corporation as a way to cope with large image files, and to enable PostScript-based desktop publishing applications such as PageMaker to work with CEPS such as Crosfield, Hell, Scitex, and Screen.
After Aldus was acquired by Adobe Systems, both the TIFF and OPI specs became the intellectual property of Adobe, which continued to publish the specification. Following its debut in 1989, the specification was upgraded to v1.3 in September of 1993. A draft of the 2.0 spec was released in August of 1995, though it remains in “draft” with the caveat that “it may change significantly before its final release.” Given its lineage, the 1.2 and 1.3 specifications sup-ported only TIFF (tag image file format) images. However, since different applica-tions generated different OPI comments that resulted in incorrect or no image substitution at all, Adobe revised the 2.0 specification to support EPS files.
Of course, OPI isn't the only image replacement system/methodology. Both Scitex and Quark developed their own tools to expedite production. Scitex devel-oped APR (automatic picture replacement) to enable designers to perform page makeup while enabling its high-end workstations to focus on image retouching. For its part, Quark developed the DCS (desktop color separation) specification, which is a derivative of EPS, to complement XPress workflows. The first release, DCS v1.O, required that images be separated into the process colors and saved along with a low-res composite file, which gave rise to its nickname as “five-file EPS.” With DCS v2.0, separated files can be saved in either a single file or multi-ple files; in addition, v2.0 supports spot colors and additional separations for applications such as HiFi color.