嫦娥三号全景相机具有彩色成像模式, 在发射前需先进行彩色定标, 样本真值的获取是彩色定标的前提。 传统方法获取的颜色真值在色差值和视觉感知上都与实际值存在明显的偏差。 若直接采用该颜色值作为真值进行彩色定标, 影响定标后的色差大小和定标校正后颜色的人眼视觉感知效果。 为探索更好的颜色真值获取方法, 利用实验室内测得的D65定标光源的相对光谱功率分布, 重新定义了转换矩阵中的白点坐标, 然后基于CIE颜色计算公式, 根据格拉斯曼颜色混合定律, 对XYZ与sRGB颜色空间之间的转换矩阵进行了修正, 提高了样本真值获取的准确度。 另外利用修正后的转换矩阵对sRGB空间的三刺激值曲线进行了重新计算, 对标准转换值偏离实际值的原因进行了分析。 通过地面试验验证, 相对于传统样本真值获取方法, 利用该真值获取方法定标后A, B两相机的色差值分别降低了0.8和0.73; 定标矩阵校正在轨图像时, 色差分别降低了26.50%和34.47%, 且校正后的颜色与人眼的视觉感知效果更接近。

Chang’E-3 panoramic camera is designed for color imaging, and a color calibration has to be performed before the launch of the detector. The first step when calibrating the camera is to obtain the ground truth color values of the samples. The color values measured by the traditional method have some significant deviations with the actual values and differ at the color difference and human visual perception. When the values are used to perform calibration, the color differences are not ideal, and the images have a negative effect on human perception. In this study, the white reference coordinates adopted in transformation matrix between XYZ and sRGB color space are redefined by using the relative spectral power distribution of D65 calibration light source. After that, based on the CIE color-computing formula and H. Grassmann color mixing law, the transformation matrix to recalculate RGB color values from XYZ color space is modified. In addition, by means of calculating spectral tristimulus values in sRGB with modified matrix, we give analysis to the factors that caused color distortions. The results of the ground experiment showed that the color differences DE76 for cameras A and B after calibration reduced 0.8 and 0.73 respectively compared with those achieved using traditional method. And when the calibrated matrix is used to correct images taken on lunar surface, color difference reduced 26.50% and 34.47% respectively, and the images have a positive effect on human perception.