Hybrid halftoning using direct multi-bit search (DMS) screen algorithm

In this paper we propose a mathematical framework for multi-bit aperiodic clustered dot halftoning based on the Direct Multi-bit Search (DMS) algorithm. A pixel validation map is provided to the DMS algorithm to guide the formation of homogeneous clusters. The DMS algorithm operates without any user defined guidance, iteratively choosing the best drop absorptance level. An array of valid pixels is computed after each iteration that restricts the selection of pixels available to the DMS algorithm, improving the dot clustering. This process is repeated throughout the entire range of gray levels to create a visually pleasing multi-bit halftone screen. The resultant mask exhibits smoother appearance and improved detail rendering, compared to conventional clustered dot halftoning. Much of the improvements originate from the improved sampling of the aperiodic hybrid screen designs.