Most printing devices, such as laser and InkJet printers, are restricted to very few colors. The continuous-tone images should therefore be transformed into binary ones before being printed. The techniques doing this transformation are referred to as halftoning methods. Halftoning methods can be divided into two main categories, namely AM (Amplitude Modulated) and FM (Frequency Modulated). In the AM method the size of the dots are changing while their frequency is kept constant, that is the darker the tone the bigger the dot. In the FM method the size of the micro dots are constant while their frequency (number of micro dots) varies. In other words the darker the tone the more the number of micro dots. Some printing methods, such as Flexography, can not produce the dots sufficiently small. Therefore, if only an AM halftoning method is used the highlights (and the shadows) of the original image can not correctly be reproduced. In this paper we present a hybrid halftoning method that incorporates AM and FM halftoning in order to overcome this problem. The proposed method uses a FM method for the highlights (and shadows) and an AM method for the rest of the original image.
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