Anti-counterfeiting features of artistic screening

Although Artistic Screening has been designed mainly for performing the creation of graphic designs of high artistic quality, it also incorporates several important anti-counterfeiting features. For example, bank notes or other valuable printed matters produced with Artistic Screening may incorporate both full size and microscopic letters of varying shape into the image halftoning process. In this contribution, we show that frequency modulated screen dots exhibit a strongly position-dependent reproduction behaviour, which is difficult to compensate with devices capable of applying a simple gamma correction curve to the whole image. We present a method for multidimensional gamma-correction, where the dot gain compensation is both dependent on the intensity and on the period of the screen element. This position-dependent dot gain correction can be embedded into any halftoning process capable of generating variable frequency screen elements. Position-dependent dot gain correction ensures the correct appearance of continuous tone images on the target printer for which the compensation tables have been established. Attempts to reproduce the image by electrophotographic means will fail due to the position dependent dot gain induced by the variable frequency screen dots. Correction of position-dependent dot gain would require a tremendous effort from potential counterfeiters