Channel dependent error diffusion algorithm for dot-off-dot printing

摘要

The simplest way of halftoning color images using error diffusion is to apply scalar error diffusion technique to each of color channels independently. When processed independently for C, M, Y and K channels, cyan and magenta dots are often printed at the same pixel location. Such overlaps between cyan and magenta would appear as color noise in highlight area. Thus, it is desirable to minimize dot-on-dot printing of cyan and magenta especially in highlight area. In order to further improve image quality, combined dot distribution of cyan and magenta should be homogeneous. Also, dot distribution of individual color channel should be even. In this paper, tone dependent error diffusion kernels and serpentine direction of processing are employed for homogeneous dot distribution of individual color channel. A decision rule based on updated values of cyan and magenta is applied to achieve dot-off-dot printing. A channel dependent threshold modulation is proposed to improve combined distribution of cyan and magenta. A criterion to measure homogeneity of dot distribution is also proposed.