# A Color Matching Method for Mosaic HY-1 Satellite Images in Antarctica
## 3 Results
### Multi-Image Color Match Results  
Four satellite images from HY-1/CZI cover the area around the Ross Ice Shelf in Antarctica. These images were taken on different dates in December 2021. Due to the differences in orbital characteristics and illumination conditions during the imaging process, obvious color differences existed in the original mosaic image from the visual effect (Figure 6b). The choice of reference image can be based on the principle of better visualization, and Figure 6a was chosen as the reference CZI Antarctic image for the next step of  
Figure 5: Comparison of the HY-1/CZI brightness nonuniformity correction for Antarctic images: (a) original CZI image, (b) nonuniformity correction results of (a), (c) original CZI image, and (d) nonuniformity correction results of (c). \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 (STD)**} & \multicolumn{3}{c}{**Result Image (STD)**} \\ \cline{2-7}  & & **R** & **G** & **B** & **R** & **G** & **B** \\ \hline
1 & 49.3 & 49.4 & 49.8 & 45.8 & 45.0 & 46.2 \\
2 & 49.1 & 53.4 & 63.2 & 17.7 & 17.9 & 17.8 \\
3 & 50.8 & 52.6 & 54.5 & 16.1 & 14.0 & 13.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Statistical results before and after image nonuniformity correction. color matching. Figure 6e is the result from our algorithm, and the threshold value T = 90 was set in the process of color matching. After color matching for the four images, the color difference between the images was significantly improved, the brightness and color of the whole mosaic image were relatively uniform, and the visual effect was effectively improved. In this experiment, we also use the general histogram specification [42] and Wallis method [20] for comparison. The general histogram specification result is shown in Figure 6c. It can be seen that the contrast becomes larger in the glacial regions. Figure 6d shows the results using the Wallis algorithm. It can be seen that the color difference between the four images has been improved appropriately, but it remains significantly different from the color of the reference image. Figure 7 shows the histograms of the reference image, original mosaic image, and mosaic image after color matching. There is an obvious difference in the distribution of gray values between the water body and the glacier in the reference image from the histogram statistics results, which also indicates the obvious difference between the low reflectance of sea and the high reflectance of glaciers in the optical image of  
Figure 6: Color matching results of the HY-1/CZI Antarctic image (the red line in the figure is the coastline): (**a**) reference image used for color matching, (**b**) original mosaic image, (**c**) general histogram specification result, (**d**) Wallis result, and (**e**) color-matching result of this paper. shows the histogram of the original mosaic image without color matching. Due to the different color tones of each image, the distribution width of gray values from sea and glaciers is larger in the histogram than that of Figure 7a. Figure 7c-e are the histograms of the general histogram specification results, the Wallis matching results, and the results of this paper, respectively. Figure 7c,e show the histogram results after image color matching, which are in better agreement with the histogram distribution of the reference image (Figure 7a). The difference between Figure 7c,e is the difference in the number of pixel distributions between the two wave peaks on the histograms. There are more dark pixels in Figure 7c, because the general histogram specification method stretches some pixels on the glacier to dark pixels, thereby increasing the color contrast on the glacier (Figure 6c). In this paper, the darker and brighter targets are corrected by setting thresholds to make the color and contrast of the glaciers more natural.