OverprintBlack (user param)

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

Controls overprinting of pure black objects, regardless of the job's overprint settings. An object is pure black if the object's color space and color values match the same conditions for black preservation (see Black preservation). Typically, the color space must be a device space, with a Black component of 100%, and other components must be 0%. It will not apply to ICCBased color spaces.

OverprintBlack is not applied to process components if the color is converted to a space where there isn't a Black component ; however, spot components of solid black objects are still overprinted.

The behaviour with each setting is: 

If false, pure black is overprinted, or not, using the same rules as other process colors.

If true, any pure black vector or text object (not images or shadings) will be overprinted, regardless of the job's overprint settings. Components with a 0% color value are overprinted. In traditional print, it is common to force black items to overprint when printed on a colored background, to avoid the risk of white lines appearing round it if there is any mis-registration on press.

If the value is /Knockout, any solid black vector or text object (not images or shadings) will knockout, regardless of other overprint settings. With UV inkjet printing, the ink for small overprinted black objects has a tendency to “float” on top of inks that have been jetted earlier but are not yet cured, distorting both the black object and anything printed in the underlying colors. It is possible to achieve much better results by forcing the black to knockout, which also helps with using less ink. Registration should be good enough because of the natural tendency of the ink films to coalesce with any other unpinned ink film around them because of surface tension.

This is seen on some non-standard devices. It also happens in transparency jobs when an object is painted into an RGB blend space, which are common in PDF.

Default: false .

See also: OverprintProcess user parameter, Overprint system parameter and setblackoverprint procedure.