Digital watermarking technology is an effective method for copyright protection of digital\ninformation, such as images, documents, etc. In this paper, we propose a high capacity text image\nwatermarking technique against printing and scanning processes. Firstly, this method obtains the\ninvariant in the process of printing and scanning under the mathematical hypothesis model of\nprint-scan transformation. Then based on the print-scan invariant, the Fourier descriptor is used\nto flip the trivial pixel points with high frequency information on the character boundary. Next,\nconsidering the resolution of the print-scan equipment and its influence on the print-scan invariant,\na quadratic quantization function is proposed to embed watermark information of multiple bits\nfor a single character. Finally, the QR code (Quick Response code) is researched, which has large\ninformation capacity, robust error correction ability and high decoding reliability. By using the QR\ncode as the watermark information, we can reduce the impact of bit error rate during watermark\nextraction, and the robustness of the watermark information can be improved. The experimental\nresults show that the proposed text watermarking algorithm has the advantages of anti-print scanning,\nanti-scaling, large capacity and good visual effects.
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