Screen-based Watermarking and Color Screen Design Based on Aperiodic Clustered-dot Halftoning

FM (Frequency modulation) halftoning (aperiodic, dispersed-dot) is widely used with inkjet printers in both low-end and high-end devices. There is a desire from customers in the commercial market to use this capability with high-end digital presses based on electrophotographic printing (EP) technologies. However, the inherent instability of the EP process challenges the achievement of satisfactory print quality with dispersed-dot, aperiodic halftoning. The direct binary search (DBS) algorithm is widely considered to represent the gold standard of dispersed-dot, aperiodic halftone image quality.

In this thesis, we adapt DBS from dispersed-dots to clustered-dots to use with the Indigo liquid EP printing technology. We present a new screen design algorithm for aperiodic, clustered-dot halftoning based on Direct Binary Search. Our screen design has a very good detail rendering capability and a very stable halftone frequency

overall. In the next part of the thesis, we introduce a new microscreen design algorithm that allows the embedding of binary metadata in an aperiodic, clustered-dot halftone image with no loss of visual quality. We describe a simple method for decoding the embedded meta-data with only a knowledge of the two microscreens used to halftone the continuous-tone image. Our results with one image demonstrate 100% recovery of the embedded metadata. In the last part of the thesis, we introduce a method for joint design of three-color CMY screen sets, which is the continuation of the work from monochrome screen design. The method we developed was deemed to be satisfactory in all aspects of halftone texture quality as a 3-screen CMY solution.