AM/FM halftoning: digital halftoning through simultaneous modulation of dot size and dot density

Conventional digital halftoning approaches function by modulating either the dot size (amplitude modulation (AM)) or the dot density (frequency modulation (FM)). Generally, AM halftoning methods have the advantage of low computation and good print stability, while FM halftoning methods typically have higher spatial resolution and resistance to moireartifacts. In this paper, we present a new class of AM/FM halftoning algorithms that simultaneously modulate the dot size and density. The major advantages of AM/FM halftoning are better stability than FM methods through the forma- tion of larger dot clusters; better moireresistance than AM methods through irregular dot placement; and improved quality through sys- tematic optimization of the dot size and dot density at each gray level. We present a general method for optimizing the AM/FM method for specific printers, and we apply this method to an elec- trophotographic printer using pulse width modulation technology.