Printing with Halftones – 3 Part Series

This month I will discuss Stochastic, FM (Frequency Modulation)  simulated process.  This is the last part of a 3 part series.  If you missed the first two months, please go back and read it. Let’s get started.

 Just to review.

Halftone is the reprographic technique that simulates continuous tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient like effect. Halftoning is commonly used for printing color photo realistic pictures. However, you can create really cool halftone designs using just one color. It looks best if the design has a lot of detail and contrast. Other factors that affect your halftone is dpi (dots per inch) resolution, lpi (lines per inch) frequency, angle and dot shape (round, square or elliptical). I’ve discussed those in earlier blogs.

Stochastic Simulated Process

Stochastic screening or FM screening is a halftone process based on pseudo-random distribution of halftone dots, using frequency modulation (FM) to change the density of dots according to the gray level desired. The stochastic screening or FM screening uses a fixed size of dots and a distribution density that varies depending on the color’s tone. An FM screen utilizes more halftone dots than an AM screen. The result is that more light is filtered by the ink and less light simply reflects off the surface of the substrate. The result is that FM screens exhibit a greater color gamut than conventional AM halftone screen frequencies.

 

 

Pros

   •     The screening of four colors is no longer made with four different angles as with the traditional screen therefore it eliminates screening moiré. All use the same angle. 22.5 is an excellent angle used for screen printing films.

   •     FM screening does not create rosette patterns.

   •     Halftone dot sizes can be as fine as 10 micrometres, which gives the product a quality comparable to that of photographic prints.

   •     The effects of misregistration are not completely eliminated, but the effect is certainly less apparent than in the traditional screening, this feature is very favorable for printing on rotary machines where the misregistration is very common due to loose screens.

Cons

The small dots used in FM screening require special care and cleanliness, especially when making films.

Until next month

Cora Kromer
cora@qdigitizing.com