Halftoning and Color Noise

摘要

A frequency modulated color halftoning algorithm is presented in this paper. Unlike the normal approach of halftoning a color image, in which the color separations of the original image are halfloned independently, the original color image is halftoned in a context dependent manner. The strategy to reduce color noise and gain control over color gamut is to prevent dol-on-dot printing as much as possible. The color shifts that might occur because of this dot-off-dot printing strategy have to be compensated before halftoning. This transformation uses some data for the printer with which the halftoned color image is supposed to be printed. The experiments verify that the color noise is notably smaller in the images that are halftoned by the proposed method compared to the images halftoned using the normal approach of halftoning color images. The method also offers the possibility of treating the color separations of the original image differently if needed. For example, the yellow separation should be treated differently from the other separations, because the yellow dots are less visible than the other color dots when they are printed on a white paper. Two criteria for objectively measuring the quality of the produced results are also discussed.