(v13) Double-dot screens

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

It is straightforward to describe a spot function which generates a cell where dots grow from more than one cluster. Version 4 has some such screens built-in (primarily to support PDF, but nevertheless available from PostScript-language jobs).

However, it is also possible to “double-up” conventional spot function screens. This can be done simply by setting a halftone key DoubleScreens to true in the halftone dictionary. This causes the spot function to be constructed twice its normal size in each direction, and applied in each quarter in turn before proceeding to the next dot. This provides for more gray-levels than could normally be achieved with a cell of the size determined by the frequency and resolution of the raster.