图像融合中的平均梯度、相关系数、信息熵、交叉熵、联合熵、均方误差、互信息、信噪比、峰值信噪比、均方根误差、空间频率、标准差、均值、扭曲程度、偏差指数等等(Evaluation indexes average gradient, correlation coefficient, entropy, cross entropy, joint entropy, mean square error, mutual information, signal-to-noise ratio, peak sign