FM halftoning via block error diffusion
Error diffusion halftoning is a popular method of producing frequency modulated (FM) halftones. In FM halftoning the dot size and shape is fixed (equal to one pixel) and the dot frequency is varied in accordance to the graylevel values of the underlying grayscale image. We generalize error diffusion to produce FM halftones with user controlled dot size and shape using block quantization and a block filter in the feedback loop. We call this modified quantization and feedback process block error diffusion. The block filters are designed from well known scalar error filter prototypes and retain their properties. Further, we show that choosing a structured block filter results in an efficient parallel implementation of block error diffusion.