Open Prepress Interface (OPI) is a standard that give users the functionality to design pages with low-resolution images and then replace those images with their respective high-resolution variants at print time. When you use low-resolution images in your production workflow, for example in QuarkXPress, file sizes are generally smaller and print times are reduced.
When you want to send a QuarkXPress page containing an OPI image (often called an 'FPO' or 'For Position Only' image) to the printer, select the OPI Active checkbox in the OPI pane of the Print dialog box. Once you've done this, you are given an option to either include images or send low resolution information. If you choose this option, comments are included in the PostScript that tells the OPI printer to replace the FPO images with their corresponding high resolution versions. OPI workfows originally supported only TIFF (Tagged Image File Format) images.OPI technology was later expanded to support EPS (Encapsulated PostScript) and DCS (Desktop Color Separation) images.
A normal OPI workflow includes the following steps:
- The image is scanned at a high-resolution and is stored on the OPI server. Depending on the OPI system used, the FPO image is generated at the same time. It is also possible that an image editing software such as Adobe Photoshop could be used to create a low-resolution variant of the FPO. The FPO image is tagged with an external name and PostScript comment that links it to the original high-resolution image.
- The FPO image is imported into the page layout application, positioned, and then resized as desired.
- When the file is printed from an application that has built-in support for OPI, such as QuarkXPress, the OPI interpreter sees the OPI comments in the Postscript file and automatically substitutes the high-resolution versions of the images before creating the final output. Typical OPI comments describe the file path, picture box dimensions, image position within the picture box etc. A sample is included below:
%ALDImageFileName: Hard Drive:Picturest:Images:imageName.tif
%ALDImageDimensions: 1021 611
%ALDImageCropRect: 15 8 1015 597
%ALDImageCropFixed: 15.147 8.413 1015.165 597.281
%ALDImagePosition: 711.492 426.248 656.529 203.149 933.618 134.88 988.582 357.979
%ALDImageResolution: 107.474 107.474
%ALDImageType: 3 8