基于飞机目标分析了NMI(归一化转动惯量)、不变矩、轮廓矩三种图像特征的不变性，提出了目标NMI 特征提取的新方法。实验表明，基于新方法提取的NMI 特征与传统的NMI 特征、不变矩提取算法相比，具有良好的平移、旋转、比例不变性，且提取方法简单，易于实现。

Invariant feature of three images such as normalized moment of inertia (NMI), invariant moment and contour moment are analyzed based on airplane targets. New extraction methods of target NMI feature are proposed. The experiment shows that NMI feature extracted with the new method has good translation, rotation and scaling invariance compared with traditional NMI feature and invariant moment extraction algorithm. And extraction method is simple and easy to implement.