Next, considering the resolution of the print-scan equipment and its influence on the print-scan invariant, a quadratic quantization function is proposed to embed watermark information of multiple bits for a single character.
Then based on the print-scan invariant, the Fourier descriptor is used to flip the trivial pixel points with high frequency information on the character boundary. Firstly, this method obtains the invariant in the process of printing and scanning under the mathematical hypothesis model of print-scan transformation. In this paper, we propose a high capacity text image watermarking technique against printing and scanning processes. Digital watermarking technology is an effective method for copyright protection of digital information, such as images, documents, etc.
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