Using background separations for crop and other marks

This page applies to Harlequin v13.1r0 and later; both Harlequin Core and Harlequin MultiRIP.

A background separation is used to provide embellishments such as separation names next to the relevant separations, job identification, color bars and gray ramps, crop marks, registration marks, and so on.

Where separations are being produced one-per-film, this could be done using BeginPage or EndPage operands of the setpagedevice operator (see Imposition) to add some graphics and adjust clipping and page position appropriately. Such marks would appear on every separation according to the color they are drawn in.

However, it is often desirable to have marks which appear per-sheet rather than per-separation (for example, a single job identifier on each sheet). This is especially true of step-and-repeat separations where typically only one set of crop-marks is required for the whole sheet, even though there may be many separations on the sheet, albeit all the same color.

The solution to this is to add extra separations containing only the embellishments, in their own spot colors, which can then be positioned independently of the main separations. This could be done with the capabilities already introduced, except that such separations would violate two of the rules for automatic separation:

• separations would overlap each other—objects always contribute at least knockouts in all separations. This produces unpredictable results.
• separations would go off the edge of the page when translated into position—each separation is bounded by all the marks on the page in all colors, and none of those marks must lie off the page when shifted into place.

Background separations, declared as such as described in Operators controlling separations, colorants, and color channels, are allowed to break these rules, so long as they meet certain rigid requirements.