# A High Capacity Watermarking Technique for the Printed Document
## 5 Conclusions  
This paper proposes a high capacity watermarking algorithm for the printed document. Our algorithm is designed by studying the print-scan process, Fourier descriptor, quantization function and the QR code. Furthermore, the performance of the proposed algorithm is compared with the previous methods to demonstrate the advantages in capacity, visual effect and robustness. Compared with the existing methods, our algorithm has the following advantages:  
1. Larger watermark capacity. This paper analyzes the accuracy of the print-scan equipment to design a suitable quantization function, and makes a reasonable balance between the visual effect and the watermark capacity, so that the watermark capacity is greatly improved. In addition, by using the quantization function, a single character can carry \(n\) bits watermark information, making it possible to embed QR code or other patterns in the document. The QR code itself has a larger information capacity, so this paper implements a large-capacity text watermarking algorithm. 2. Better visual effect. Compared with the existing methods, this algorithm has a better visual effect and the visual effect can be adjusted according to the actual situation. This visual effect has strong generality, both English and Chinese fonts have good results. 3. Better robustness. This algorithm can resist the attack of print-scan process, the attack of image scaling, the attack of noise and many more, and this algorithm can realize the blind extraction. Moreover, in order to further reduce the influence of the extraction error rate, this paper proposes to use the QR code as the watermark information. Since the QR code itself has an error correction function, the information carried by the QR code can still be scanned within a certain error range, thereby making the robustness better. It should be noted that this algorithm needs to design the quantization function according to the error range produced by the print-scan equipment. For different printing and scanning equipment, \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Num** & **Author-Year** & **No Attack** & **5\% Noise** & **50\% Size** & **200\% Size** & **PS (Print-Scan)** \\ \hline \multirow{2}{*}{1} & \multirow{2}{*}{[21]-2008} & Number of the error & \multirow{2}{*}{ERR-3} & \multirow{2}{*}{ERR-5} & \multirow{2}{*}{ERR-1} & \multirow{2}{*}{ERR-8} \\  & & bits (ERR)-0 & & & & \\ \multirow{2}{*}{2} & \multirow{2}{*}{[22]-2019} & ERR-0 & ERR-2 & ERR-4 & ERR-2 & ERR-7 \\  & Proposed method & ERR-0 & ERR-3 & ERR-4 & ERR-1 & ERR-9 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Bit error rate of different models under various attack conditions. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Num** & **Author-Year** & **Arial 14 pt** & **TNR 14 pt** & **LiSu 14 pt** & **KaiTi 14 pt** & **Century 14 pt** \\ \hline
1 & [21]-2008 & 94.50\% & 93.97\% & 93.69\% & 94.75\% & 95.48\% \\
2 & [22]-2019 & 95.97\% & 95.18\% & 94.88\% & 96.18\% & 95.41\% \\
3 & Proposed method & 97.29\% & 97.15\% & 96.12\% & 97.79\% & 97.44\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The SIM value of different models. the quantization function may be different and the visual effects will be different. In addition, the boundary flipping strategy can also be optimized when there are many character boundary points. Moreover, for the improvement of robustness, other better error correction and verification schemes can be designed to reduce the impact of bit error rate during the extraction process. For example, the two-layer cellular neural network (CNN) architectures proposed in literature [32] are very suitable for generating highly robust watermarking patterns. In general, the research of text watermarking algorithm is still essential, and the research space is still very broad. In addition, for further work, we will focus on optimizing this algorithm with neural network, enhancing the security of watermark information and implementing this algorithm in a consumable SoC of printer. Conceptualization, K.H. and X.T.