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 or AM) or the dot density (frequency modulation or FM). Generally, AM halftoning methods have the advantages of low computation and good print stability, while FM halftoning methods typically have higher spatial resolution and resistance to Moiré artifacts. In this paper, we present a new class of AM/FM halftoning algorithms that simultaneously modulate dot size and density. The major advantages of AM/FM halftoning are: • Better stability than FM methods through the formation of larger dot clusters. • Better Moiré resistance than AM methods through irregular dot placement. • Improved quality through the systematic 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 electro-photographic printer using pulse width modulation (PWM) technology.