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HCS - Harlequin Chain Screening. Harlequin Chain Screening (HCS) gives an overall triangular pattern and produces a very fine rosette structure. This screening method is particularly suited to printing charts, weather maps and other computer-generated graphics. HCS uses a long elliptical dot, instead of conventional symmetrical dot shapes. This creates smooth flat tints and vignettes even when working at low-screen rulings. Consequently, the technique may be applied anywhere from flexography and newspaper printing to printing on cover stock at 175 lpi ruling.
Harlequin Chain Screening uses a long ratio elliptical dot. When used for process color separations the angles used are 60° apart, rather than the more common 30° apart used for most offset litho work. This gives an overall triangular pattern and produces a very fine rosette structure. The angles used are -45, 45, -15, and -75 degrees for yellow, magenta, cyan, and black respectively. When used at high frequencies, this screening set is extremely good at holding detail in continuous tone areas (e.g. scanned images), but can suffer from worse object moiré than, for example, elliptical dots if the subject of the image contains fine patterns. It is also very good at creating smooth, flat looking tints in process color work even at low screen rulings, although care must be taken at the edges of such tints, where patterns can occur unless they are bounded, e.g. with a black rule. The screen frequency keyed into the RIP will be used for HCS screens, but the angle will be ignored and an angle selected automatically based on the color separation being processed.
HMS - Harlequin Micro Screening. Developed to meet the unique requirements of specialty printers, HMS takes advantage of the benefits of higher screen rulings by enhancing highlight printability. High key pictures to be printed at high rulings on good coated stock are well suited for Harlequin Micro Screening. This screening method allows higher detail with minimized moiré by making it possible to print at high screen rulings (above 150 lpi) without loss of highlight detail. It allows running at higher screen rulings even with plates and press equipment that normally would not be able to reproduce the resultant small highlight dots. Harlequin Micro Screening uses a Respi screen structure to allow greater highlight gradation even at high screen rulings. It does this by using half the nominal screen between 0 and 5% dot area and between 95 and 100% and the nominal screen ruling between 20% and 80% dot area. Between 5 and 20%, and between 80 and 95% HMS goes through transition zones. Two variants of HMS are included in HSL; one where the dot shapes in the 20 to 80% tints are very similar to the standard Euclidean dot shape, and one where they closely resemble the standard Elliptical shape.
If you are currently limiting the screen frequencies that you use because you cannot be certain of holding the small highlight and shadow dots with finer screens then HMS should allow you to output at significantly higher frequencies. It will, however, not assist if you need to limit your screen frequencies because of press registration problems. HMS may be used to extend the length of print runs in situations where this is normally limited by drop-out increasing as the print run progresses. HMS will act on both the screen frequency and angle as defined on the Screening or Separations dialog in the RIP.