Abstract
Digital watermarking technology is an effective method for copyright protection of digital information, such as images, documents, etc. In this paper, we propose a high capacity text image watermarking technique against printing and scanning processes. Firstly, this method obtains the invariant in the process of printing and scanning under the mathematical hypothesis model of print-scan transformation. 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. 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. Finally, the QR code (Quick Response code) is researched, which has large information capacity, robust error correction ability and high decoding reliability. By using the QR code as the watermark information, we can reduce the impact of bit error rate during watermark extraction, and the robustness of the watermark information can be improved. The experimental results show that the proposed text watermarking algorithm has the advantages of anti-print scanning, anti-scaling, large capacity and good visual effects.
Highlights
With the development of the Internet, data and information are ubiquitous in our daily life, and information exchange is becoming more frequent
The digital watermarking technology is relatively mature for images because they have a lot of redundant information to embed watermark, and these algorithms usually use the information in frequency domain of image for watermark embedding
This paper proposes to use the QR code as the watermark information, and use the error correction and verification functions of the QR code to improve the robustness of the watermark
Summary
With the development of the Internet, data and information are ubiquitous in our daily life, and information exchange is becoming more frequent. The text structure-based methods embed the watermark information by adjusting some features of text, such as line spacing, word spacing, and punctuation position. Word-shift coding uses the word spacing to embed watermark information These methods cannot resist the influence of text format changes, and the watermark capacity is relatively small. Alattar et al [11] use line-shift coding and word-shift coding to embed watermark information together, and add error correction technology to resist attacks. This paper proposes a text watermarking algorithm that is resistant to print-scan and can embed information at large capacities. The algorithm increases the watermark capacity by more than 200%, and the performance is improved in terms of robustness, visuality and bit error rate
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