A new approach to color correction and equalization for generating mars global color image mosaics from Tianwen-1 MoRIC images

Abstract

Mars is rich in color information, and color images can more accurately represent the surface morphology of Mars, aiding in the interpretation of its geomorphological and geological characteristics. Obtaining complete, consistent, well-quantified, and intuitive colors of Mars from remote sensing is challenging due to the instrument limitations, varying the illumination and atmospheric conditions, the dynamics of active geomorphology. Moderate Resolution Imaging Camera (MoRIC) and Mars Mineralogical Spectrometer (MMS) onboard the Tianwen-1 orbiter achieved the global coverage of Mars stereo images and the global spectral measurements in the visible and near-infrared bands. However, due to the effects of illumination and atmospheric conditions, there are obvious north–south stripes in the MoRIC color mosaic map, and the overall color tone is significantly reddish. The color difference analysis shows that the color variation in the high-latitude region of the Northern Hemisphere is mainly caused by different atmospheric conditions at the time of imaging, while in the middle and low latitude regions, it is primarily due to varying lighting conditions. In the high-latitude region of the Southern Hemisphere, the color difference is mainly caused by changes in features associated with the seasonal melting of the polar cap. In this work, we used MMS spectral data to establish Martian surface standard colors and presented a novel approach of quantified color correction and equalization for generating Mars global color image mosaics from MoRIC images. This method adjusts the brightness and tone of the images under different imaging conditions to achieve visual consistency and maintain the tonal consistency of similar features globally. The majority (80.1 %) of the overlapping areas with color differences are concentrated in ΔE00 ≤ 3.0, which significantly improves the color and brightness inconsistency of the origin. The final global color mosaics map with a spatial resolution of 76 m shows a “terracotta tone,” which we expect for Mars images, and is a good approximation of what the human eye might see.