MultiDot – nowa idea rastrowania AM

MultiDot – the new AM screening concept

 Screening technology let reproduce continuous tone images using bilevel printing method (as f.e. offset). Some properties of human eye allows the  correct reception of the continuous tone image. One have to remember, that tonal value (caused by surface covered by printing elements only) existing on the printing plate is not the same as the one present on the printout.  In offset printing technology the difference between tonal value on the printing plate and on the printout is provoked by two different  phenomenons: one is  the Dot Gain, while the other is caused by driving the ink out by dampening solution.

The Dot Gain effect has 3 main reasons:

·         spilling out of the ink on the printed surface,

·         deformation of  transfer medium (f.e. offset blanket) - present only when indirect printing technology is in use

·       “shadow” of the printing ink layer.

... and is well defined and known. The mutual  (the  ink and the water/dampening solution) influence is very difficult to predict using mathematic formulas.

We can observe, that (because of the Dot Gain effect)  there are some areas not covered by ink, but absorbing the light as they would be – so it can be a base for some ink saving – if the effect would be used properly.

However the FM screening has significant  DotGain effect (so ink saving should be noticeable), it demonstrates lot of  disadvantages: less print stability, unevenly flat areas and many, many  others.

To fulfill some expectations the new AM screening was developed (and patented). It was named MultiDot and is based on multi-cluster principle, where – what’s important –  single clusters have different size and shape. Optimal shape and tonal function caused, that newly developed screening concept let the user receive stable, rich in details and Moire free images with significant ink-saving capabilities.

The other aspect of  using MultiDot screening structure is to prevent prints against illegal copying and allowing the user  to confirm (or deny) the authenticity of certain printouts or goods – this functionality is called  MultiDot Security and will be a subject of another article.