Halftone screens

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

This chapter describes how screening can be controlled in the Harlequin RIP. It doduments many extensions to standard screening, and describes the additional screens and screening engines provided.

The Harlequin RIP incorporates proprietary algorithms for halftone screening, known as Harlequin Precision Screening (HPS^™ ). These algorithms provide moiré-free screening for color reproduction. This chapter describes methods for controlling HPS from PostScript-language extensions; for the most part, the controls are system parameters. HPS does not rely on specialized sets of frequencies and angles, so the controls are mainly for tuning memory use and performance. Many of these controls are available from dialogs in HMR, so the PostScript-language varieties will not often be needed explicitly in that version.

The RIP also provides methods for overriding various aspects of screens set by the job, whether or not HPS is involved - for example, the frequency and spot shape; again, HMR layers dialogs on top of the PostScript-language controls. As well as obtaining a more controlled result, these techniques can make processing a job significantly faster.

Halftone screens have historically been abused to produced special pattern effects. We call these pattern screens. Because of the problems this causes - for example with calibration, or when outputting to a contone device - the RIP detects pattern screens and replaces them with alternatives.