# Reversible Image Processing for Color Images with Flexible Control
## 4 Experimental Results
### Visual and Quantitative Evaluation  
First, we visually evaluated the output images with brightness control or saturation improvement. Figures 5 and 6 shows the raw image and output images derived with the proposed method and previous methods [1; 12]. In this experiment, we defined \(I_{VSH}=I_{VSM}=2\), \(I_{VI}=I_{VD}=I_{VC}=30\), and \(I_{S}=20\). Figures 5b-f and 6b-f demonstrate that \begin{table}
\begin{tabular}{l c c} \hline
**Database** & **\# of Images** & **Image Size** \\ \hline Kodak [21] & 24 & \(768\times 512\) \\ \hline SIPI [22] & 6 & \(512\times 512\) \\ \hline McMaster [23] & 18 & \(500\times 500\) \\ \hline IHC [24] & 6 & \(4608\times 3456\) \\ \hline ITE [25] & 10 & \(1920\times 1080\) \\  & & (converted from bit depth of 48 to 24) \\ \hline \end{tabular}
\end{table} 
Table 1: Test images. the proposed method effectively executed a single brightness control from among the five types: sharpening and smoothing, increase and decrease, and CE. As can be seen in Figures 5g and 6g, we can verify that our new method practically improved the saturation. In regard to the previous methods [1; 12], they also enhanced the contrast as shown in Figures 5h,i and 6h,i. These previous methods, however, cannot carry out other types of brightness controls and saturation improvement. Furthermore, Figures 5i and 6i reveal that the previous method [1] caused hue distortion with the CE function. Next, we quantitatively confirmed the availability of brightness control, saturation improvement, and hue preservation functions. Table 2 shows the mean value of each evaluation index for all the test images under different parameters. Note that \(I_{S}=0\) means that the saturation is intact. In the case of the sharpening or smoothing function, the differences in standard deviations between the raw and output images increased or decreased. The brightness differences increased or decreased depending on the brightness increase or decrease function. With respect to the CE function, the RCE values exceeded 0.5 for the proposed and previous methods. The saturation differences increased in response to the saturation improvement function. In regard to the hue, the absolute differences were relatively small for the proposed method and previous method [12], while that of the previous method [1] was considerably large. From the aforementioned results, we verified that the proposed method has flexible functions for brightness and an improvement function for saturation without distorting the hue. Figure 5: Raw image and output images from proposed and previous methods [1; 12] (kodim11). (**a**) Raw image. (**b**) Sharpening (\(I_{VSH}=2\)). (**c**) Smoothing (\(I_{VSM}=2\)). (**d**) Brightness increase (\(I_{VI}=30\)). (**e**) Brightness decrease (\(I_{VD}=30\)). (**f**) CE (\(I_{VC}=30\)). (**g**) Saturation improvement (\(I_{S}=20\)). (**h**) CE under previous method [12] (\(I_{VC}=30\)). (**i**) CE under previous method [1] (\(I_{VC}=30\)). The proposed method has many advantages over the previous methods [1; 12], but there still exists a constraint. To ensure reversibility, our new method requires the recovery information of the system.