A New Multi-set Modulation Technique for Increasing Hiding Capacity of Binary Watermark for Print and Scan Processes

In this paper we propose a multi-set modulation technique to increase the hiding capacity within a binary document image. As part of this technique we propose an Automatic Threshold Calculation and Threshold Buffering, Shifted Space Distribution and Letter Space Compensation technique. The Automatic Threshold Calculation is used to distinguish word spaces from letter spaces. The Threshold Buffering is used to reduce the chance of misinterpretation of spaces during the detection phase, following printing and scanning. The Shifted Space Distribution and Letter Space Compensation techniques robustly embed a watermark into the binary document image. The Automatic Threshold Calculation has been shown to be successful in identifying word spaces for different types of fonts and font sizes. The combination of the Shifted Space Distribution, Letter Space Compensation and Threshold Buffering techniques have been shown to create a watermark that is robust to printing and scanning.