The overlapping of black dot decreases brightness and black dot is very sensitive to the human visual system in the bright region. In this paper, for gray-level expression, only the bright gray region in the color image was considered for blue noise mask (BNM) approach. To solve this problem, BNM with CMY dot was used for the bright region instead of black dot. We dispersed CMY dots spatially. At first, the threshold was decided to avoid pixel overlap. Below the threshold, BNM was processed and black dots were assigned. Above the threshold, we assigned the corresponding gray level into cyan, double of gray level into magenta, and three times of gray level into yellow. CMY binary dot was made by using BNM. If all cyan, magenta, and yellow dots overlapped, cyan dots were printed only. If magenta and yellow dots overlapped, magenta dots were printed. Finally, we obtained an output image which was composed of black, cyan, magenta, and yellow pixels. Dot-on-dot model with single mask caused problems making black dots overlap, leading to color distortion. Therefore, an approach with three rotated-masks for C, M and Y each was proposed to decrease pixel overlap and color distortion.
Yun-Tae Kim, Jeong-Yeop Kim, Hee-Soo Kim, Yeong-Ho Ha, "Halftoning Method by CMY Printing Based on BNM" in Proc. IS&T 8th Color and Imaging Conf., 2000, pp 252 - 256, https://doi.org/10.2352/CIC.2000.8.1.art00046