# Reversible Data Hiding in Encrypted Images Based on the Mixed Multi-Bit Layer Embedding Strategy
## 4 Experimental Results and Discussion
### Image Quality Analysis  
The receiver needs to decrypt and restore the transmission image. Below is an analysis and comparison of the recovery quality of the cover image. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Image**} & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON] [22]** & **[PERSON] [23]** & **[PERSON]** [24]** & **[PERSON]** & **[PERSON]** [34]** & **Proposed** \\  & **[14]** & **[15]** & **[18]** & **[19]** & **[20]** & **[PERSON] [22]** & **[PERSON] [23]** & **[24]** & **[24]** & **[34]** & **[34]** & **Proposed** \\ \hline Lena & 0.024 & 0.015 & 0.25 & 1.4 & 0.88 & 0.811 & 0.886 & 0.0325 & 1.192 & 1.796 & 1.83 \\ Airplane & 0.019 & 0.015 & 0.25 & 1.57 & 0.72 & 0.796 & 0.918 & 0.0325 & 1.22 & 1.832 & 2.22 \\ Peppers & 0.016 & 0.015 & 0.25 & 1.36 & 0.82 & 0.663 & 0.624 & 0.0325 & 1.173 & 1.844 & 1.79 \\ Baboon & 0.005 & 0.015 & 0.25 & 0.47 & 0.23 & 0.377 & 0.741 & 0.0325 & 0.316 & 0.484 & 0.54 \\ Average & 0.016 & 0.015 & 0.25 & 1.2 & 0.663 & 0.662 & 0.792 & 0.0325 & 0.975 & 1.489 & 1.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of the maximum embedding capacity for different schemes (/bpp). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Image**} & **Embedding Rate** & **PSNR of the** & **PSNR of the** \\  & **\(T\)** & **/bpp** & **Decrypted Image/dB** & **Recovered Image/dB** \\ \hline Lena & 4 & 0.32 & 47.06 & +\(\infty\) \\  & 8 & 1.47 & 40.16 & +\(\infty\) \\  & 16 & 1.83 & 34.92 & +\(\infty\) \\  & 32 & 1.8 & 30.54 & +\(\infty\) \\  & 64 & 1.64 & 26.73 & +\(\infty\) \\ Airplane & 4 & 1.27 & 46.27 & +\(\infty\) \\  & 8 & 2.03 & 41.08 & +\(\infty\) \\  & 16 & 2.22 & 36.65 & +\(\infty\) \\  & 32 & 2.19 & 32.12 & +\(\infty\) \\  & 64 & 2.06 & 27.55 & +\(\infty\) \\ Peppers & 4 & 0.02 & 47.75 & +\(\infty\) \\  & 8 & 1.25 & 40.12 & +\(\infty\) \\  & 16 & 1.79 & 34.44 & +\(\infty\) \\  & 32 & 1.75 & 30.86 & +\(\infty\) \\  & 64 & 1.6 & 27.58 & +\(\infty\) \\ Baboon & 4 & / & / & / \\  & 8 & / & / & / \\  & 16 & 0.26 & 35.75 & +\(\infty\) \\  & 32 & 0.54 & 28.54 & +\(\infty\) \\  & 64 & 0.48 & 22.46 & +\(\infty\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Experimental results with different \(T\). Figure 8 shows the results of related schemes. [PERSON] [14] made a data extraction error in the non-smooth area, which affected image recovery. [PERSON] [17] and [PERSON] et al. [24] used the MSB of adjacent pixels for data decryption and recovery. [PERSON] et al. [22] and [PERSON] [23] used traditional RDH methods such as histogram shift for hiding and data recovery. [PERSON] et al. [30] realized data recovery through multi-round extraction of block-level prediction error. The decryption performance of the proposed scheme in this paper is about 30-65 dB on the image with a smooth texture. At 1 bpp, the range of PSNR fluctuates from 40 dB to 50 dB and can be maintained at about 30 dB+ at the maximum embedding rate. On the Baboon image with a complex texture, its decryption performance decreases. Still, it is relatively stable as a whole and is slightly lower than 30 dB at the maximum embedding rate, which does not affect the use. At the same time, in [14; 17; 24], the cover can be completely reversible only when certain conditions are met. However, Refs [22; 23; 30] and the proposed scheme can realize the real reversibility of the cover image. In general, when the PSNR is greater than 30 dB, it is considered to have good visual quality. Therefore, the proposed scheme can achieve better decryption performance than other schemes. Table 5 shows other metrics comparisons of the proposed scheme with the related works. Column 2 gives a comparison of the separability of each scheme. Among them, schemes [14; 15; 16; 30] adopted the joint method at the receiver, but the other schemes adopted the separable method to achieve more flexibility. During the data recovery extraction phase, the data accuracy cannot be fully guaranteed in [14; 15; 16], and the recovered image is lossy.