# Reversible Image Processing for Color Images with Flexible Control
## 4 Experimental Results
### Effectiveness of Embedding Process  
We compared the amount of recovery information with the hiding capacity. The previous methods [1; 12] with the CE function used the RDH-based HS method [1] to enhance the contrast and embed the recovery information simultaneously. The proposed method also uses the RDH-based HS method for the CE function. If the amount of recovery information for CE exceeds the hiding capacity, then the residual information will be embedded later with the other recovery information in the proposed method. The recovery information for the other functions and the above residual information for CE were embedded using the PEE-HS method [19].  
Figure 9 exhibits the hiding capacity, amount of the recovery information, and proportion of recovery information to the hiding capacity in the RDH-based HS and PEE-HS methods, where \(I_{VSH}=I_{VSM}=2\), \(I_{VI}=I_{VD}=I_{VC}=30\), and \(I_{S}=20\). The proportion of recovery information to the hiding capacity is defined as  
\[\begin{split} Proportion\ of\ recovery\ information\ to\ hiding\ capacity\ [\%]\\ =\frac{Amount\ of\ recovery\ information}{Hiding\ capacity}\times 100.\end{split} \tag{9}\]  
In Figure 9c,f, all of the recovery information can be perfectly embedded when the index indicates a value less than 100%.  
Figure 8: Maximum level of each evaluation index. (**a**) Difference in standard deviations. (**b**) Brightness difference. (**c**) RCE for proposed and previous methods [1; 12]. (**d**) Saturation difference.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & **PSNR (dB)** & **SSIM** & **CIEDE2000** \\ \hline Sharpening & \(I_{VSH}=2\) & & & \\ \hline Smoothing & \(I_{VSM}=2\) & & & \\ \hline Brightness increase & \(I_{VI}=30\) & \(+\infty\) & 1.0000 & 0.0000 \\ \hline Brightness decrease & \(I_{VD}=30\) & & & \\ \hline CE & \(I_{VC}=30\) & & & \\ \hline Saturation improvement & \(I_{S}=20\) & & & \\ \hline CE by prev. [12] & \(I_{VC}=30\) & 59.16 & 0.9992 & 0.1001 \\ \hline CE by prev. [1] & \(I_{VC}=30\) & \(+\infty\) & 1.0000 & 0.0000 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Quality of restored images.  
Figure 9a-c shows the results for the CE function using the HS method for each method. As can be seen in these figures, the previous methods [1,12] constantly embedded the entire recovery information. On the contrary, in the proposed method, the amount of recovery information was larger than the hiding capacity for several images. In such a case, the residual information would be embedded with the PEE-HS method as mentioned below.  
Figure 9d-f exhibits the results for all the functions using the PEE-HS method in our new method. With respect to the CE function, the above residual information and the other essential recovery information were embedded in this process. In the other functions, all of the recovery information was embedded at once. According to these figures, it is clear that the proposed method could perfectly embed all of the recovery information in any function. Note that we calculated the hiding capacity under the condition that the PEE-HS method was carried out with a single repetition to ensure a sufficient capacity. The number of processing times was variable, depending on the amount of recovery information to be embedded.