## 3 Proposed Method
### Image Encryption
Our experiments show that for images with complex textures there are a large number of 2 \(\times\) 2 sized pixel blocks in the block structure after AQP. Since four 2 \(\times\) 2 sized pixel blocks are used as the processing unit in the proposed method, when all four 2 \(\times\) 2 sized pixel blocks are usable for the same pixel blocks, the proposed method requires 15 tagging bits, and [13] requires 12 tagging bits, while [14] requires 18 tagging bits. The increase in the number of tagging bits will lead to a reduction in the embedding capacity. Since the \begin{table}
\begin{tabular}{c c c} \hline \hline  & **The Proposed Method Compared** & **The Proposed Method Compared** \\  & **with [13]** & **with [14]** \\ \hline EC\({}_{1}\) & 674,057 & 669,028 \\ EC\({}_{2}\) & 272,838 & 535,398 \\ \(\Delta\)EC\({}_{1}\) & 59,565 & 12,347 \\ \(\Delta\)EC\({}_{2}\) & 8311 & 5381 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The embedding performance analysis of the proposed method compared with method [13] and method [14]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{4}{c}{**EC (bit)**} \\ \hline Image & [13] & [14] & [16] & [20] & [25] & Proposed method \\ Barbara & 327,263 & 349,297 & 34,342 & 253,567 & 25,180 & 347,916 \\ Boat & 334,343 & 386,905 & 27,262 & 259,864 & 29,561 & 376,904 \\ F16 & 492,674 & 534,581 & 73,139 & 260,208 & 48,722 & 551,018 \\ House & 419,121 & 440,927 & 44,009 & 261,024 & 26,058 & 446,916 \\ Lake & 306,395 & 349,582 & 29,750 & 259,896 & 25,137 & 346,679 \\ Peppers & 384,993 & 445,527 & 41,419 & 260,304 & 46,686 & 435,966 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of embedding capacity among the proposed method and prior methods. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Average**} & \multicolumn{2}{c}{**Highest**} & \multicolumn{2}{c}{**Lowest**} \\  & **EC (bit)** & **ER (bpp)** & **EC (bit)** & **ER (bpp)** & **EC (bit)** & **ER (bpp)** \\ \hline Method [13] & 593,090 & 2.2625 & 1,351,139 & 5.1542 & 50,273 & 0.1918 \\ Method [14] & 638,698 & 2.4364 & 2,045,606 & 7.8034 & 15,444 & 0.0589 \\ Proposed method & 648,298 & 2.4731 & 2,045,750 & 7.8039 & 16,150 & 0.0616 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of the embedding performance on 10,000 images selected from the BOSS-base1.01 database between the three methods. proposed method requires three fewer tagging bits than [14] for the same pixel block, the amount of reduction in the proposed method is lower than [14] when both embedding capacities are reduced, compared to [13]. When there are unusable blocks in four \(2\times 2\) sized pixel blocks for the same pixel blocks, the tagging bits required by the proposed method are calculated as in (14), 12 tagging bits are required by [13] and the tagging bits required by [14] are calculated as in (15):

\[tb =7+t\times 3 \tag{14}\] \[tb =6+t\times 3 \tag{15}\]

where \(t\) is the number of usable blocks in the unit. It can be concluded that when the number of usable blocks is 1, compared with [13] the proposed method uses fewer tagging bits, but one more tagging bit than the [14]. Therefore, in the same case, compared with [13] the embedding capacity can be improved, and compared with [14] the embedding capacity will be reduced by one bit. When the number of usable blocks is greater than or equal to 2, the proposed method will use \((t\,\times\,3-5)\) more tagging bits than [13] and also one more tagging bit than [14]. Therefore, in the same case, compared with [13] the embedding capacity will be reduced \((t\,\times\,3-5)\) bits, and compared with [14] the embedding capacity will be reduced by 1 bit. ## 5 Conclusions

Based on the AQP and MSB prediction method, this paper proposes a large-capacity RDH-ED method. According to the pre-set threshold \(T\) and the texture complexity of the image, the AQP is used to make full use of the redundancy between pixels and vacate more embedding space. Pixel modulation is carried out for the KPA attack, which improves the security of the method.