(v13) 2-bit and 4-bit screening support

This page applies to Harlequin v13.1r0 and later; and to Harlequin Core but not Harlequin MultiRIP.

Many inkjet presses either use grayscale heads, or are configured such that multiple nozzles jet onto the same location, so that each “pixel” on the substrate can be marked with several different amounts of ink. In these cases “multi-level screening” must be used to print at the highest quality.

This section also applies to electrophotostatic (EP, toner-based) printers, which support multiple different charge levels.

Harlequin Core can apply screening for any number of colorant levels, from one (binary screening) to 15. In each case the output is then packed into the most efficient number of bits per colorant per pixel: one bit for one level, two bits for two, or three levels and four bits for four to 15 levels.

The recommended method for multi-level screening is to use HalftoneType 1009. For more information see Technical Note Hqn094: Mixing multi-bit screens.

Use of type 1009 halftones requires a license for the MLS-Mix layered option.

Installing the Advanced Inkjet Screens into Harlequin Core adds a number of example test configs, showing how multi-level screening may be configured.

In addition, you may use the AIS Tools to construct Type 1009 halftones and to select an optimal set of tonal ranges for output.

Older methods for generating multi-level screened output are now deprecated, including:

• Increasing ValuesPerComponent in the page device (for example, to 4 for 2-bit). This mechanism gave very non-linear density curves on most devices, often yielded texture banding at the points where a graduation moved from one colorant level to the next, and did not provide a simple mechanism for a number of colorant levels that did not fill the bits available.
• Use of the Depth key in HalftoneType 3 and 6. This mechanism gave complete control over pixel selections, but no tooling was provided for constructing suitable halftones.

Custom halftone modules may also be used to apply multi-level screening.