Halftoning and Multitoning
The quickest way of understanding what are halftoning and multitoning is taking a look at wikipedia. Also, I've released the corresponding source codes to my toolkit called pixkit. They are mainly implemented in C++ with OpenCV. Feel free to use them in your research :)
Below are my published papers and I also generate results with some of them to visualize their difference for comparison. The used image, Lion Fish, can be found below.
pixkit: halftoning and multitoning]