Abstract

The process of digital halftoning replaces a visually continuous tone image with a binary image in such a way as to give the illusion of multiple gray levels with the introduction of a minimum amount of artifacts or structure not present in the original continuous tone image. In this investigation we generated nonperiodic noise patterns which were uniformly distributed, so as to maintain good continuous tone reproduction, and had a prescribed 2-D spatial correlation. The spatial correlation of the noise was chosen in an attempt to reduce the undesirable artifacts introduced into the halftone image. The noise used in the halftone screen has a spectrum which is lacking low frequency power, the power is located mainly at the higher frequencies where it is much less noticeable to the visual system. This type of power spectrum is sometimes referred to as blue noise. Using an iterative process to generate these noise patterns, it is not only possible to attenuate the low frequency power, but to also concentrate the high frequency power off the horizontal and vertical frequency axes where the visual system is most acute.

© 1989 Optical Society of America