# A Color Matching Method for Mosaic HY-1 Satellite Images in Antarctica
## 4 Analysis and Discussion
### Image Quality Analysis
As a result, the distribution contrast of the image gray value in regions A and C is increased after color matching. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Index**} & \multirow{2}{*}{**Region**} & \multirow{2}{*}{**Image Category**} & \multicolumn{3}{c}{**Band**} & \multirow{2}{*}{**Average**} \\ \cline{3-4} \cline{6-6}  & & **R** & **G** & **B** & \\ \hline \multirow{6}{*}{\(\Delta\)m} & \multirow{3}{*}{A} & Original image & 25.74 & 26.03 & 22.55 & 24.77 \\ \cline{3-6}  & & Histogram specification & 24.84 & 25.19 & 24.19 & 24.74 \\ \cline{3-6}  & & Wallis & 29.40 & 28.26 & 27.96 & 28.54 \\ \cline{3-6}  & & Our result & 9.19 & 11.07 & 11.57 & 10.61 \\ \cline{3-6}  & & Original image & 12.44 & 10.33 & 2.11 & 8.29 \\ \cline{3-6}  & & Histogram specification & 13.60 & 12.06 & 9.79 & 11.82 \\ \cline{3-6}  & & [PERSON] & 8.84 & 8.14 & 7.91 & 8.30 \\ \cline{3-6}  & & Our result & 0.52 & 0.37 & 1.55 & 0.81 \\ \cline{3-6}  & & Original image & 32.43 & 33.67 & 33.40 & 33.16 \\ \cline{3-6}  & & Histogram specification & 13.98 & 15.00 & 15.03 & 14.67 \\ \cline{3-6}  & & [PERSON] & 1.22 & 0.41 & 1.44 & 1.02 \\ \cline{3-6}  & & Our result & 11.27 & 12.43 & 12.66 & 12.12 \\ \hline \multirow{6}{*}{\(\Delta\)m} & \multirow{3}{*}{D} & Original image & 15.05 & 10.69 & 3.68 & 9.81 \\ \cline{3-6}  & & Histogram specification & 5.78 & 3.32 & 6.84 & 5.31 \\ \cline{1-1} \cline{3-6}  & & [PERSON] & 13.19 & 12.31 & 11.64 & 12.38 \\ \cline{1-1} \cline{3-6}  & & Our result & 1.62 & 0.80 & 0.97 & 1.13 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Statistical results of image color matching. Figure 8: Overlapping regions (A, B, C, D) used for image quality evaluation. The average gradient is another image quality index, which reflects the detailed information of the image and indicates the richness of the detail contrast [21; 39]. The calculation formula is as follows:  
\[\
abla\text{G}=\frac{1}{\text{MN}}\sum_{i=1}^{\text{N}}\sum_{j=1}^{\text{M}} \left[\Delta_{i}\text{f}(i,j)^{2}+\Delta_{j}\text{f}(i,j)^{2}\right]^{1/2} \tag{10}\]  
where \(\
abla\text{G}\) is the average gradient; \(\Delta_{i}\text{f}(i,j)\) and \(\Delta_{j}\text{f}(i,j)\) represent the pixel gradient in the row and column directions, respectively and M and N are the row and column numbers of the image, respectively. Generally, the larger the average gradient is, the larger the image contrast is and the more details the image contains, but the ideal image should retain rich texture information and reasonable contrast, not excessive contrast. Figure 9 shows a comparison between the original image and the color-matched results of this study in some detailed areas. These sample areas include the typical feature distribution of Antarctica, including glaciers, mountains, bare rocks, and blue ice. After color matching, the colors of the resulting images have good consistency. Table 6 shows the average gradient values before and after color matching of the above seven feature sample areas. The statistical results show that the average gradient of each image after color matching is increased appropriately compared with the original image, which indicates that the details and contrast of the resulting image are enhanced to a certain extent. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Band**} & \multirow{2}{*}{**Image No.**} & \multicolumn{3}{c}{**Original Image**} & \multicolumn{3}{c}{**Result Image of This Paper**} \\ \cline{3-7}  & & **R** & **G** & **B** & **R** & **G** & **B** \\ \hline
1 & 9.6 & 9.4 & 9.5 & 10.9 & 10.7 & 10.5 \\
2 & 1.6 & 1.6 & 1.9 & 1.8 & 1.7 & 1.9 \\
3 & 4.6 & 4.5 & 4.6 & 5.7 & 5.5 & 5.6 \\
4 & 1.8 & 1.6 & 1.8 & 2.6 & 2.5 & 2.6 \\
5 & 2.6 & 2.5 & 2.7 & 3.5 & 3.3 & 3.5 \\
6 & 5.3 & 5.2 & 5.3 & 6.6 & 6.3 & 6.3 \\
7 & 6.3 & 6.1 & 6.4 & 7.3 & 7.0 & 6.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Statistics of the average gradient before and after image color matching.