sift

代码说明：

  SIFT 算法的实质上是提取局部特征的算法, 该算法在尺度空间寻找极值点, 然后根据极值点来获得尺度、旋转不变量和位置等特征。(In essence, the SIFT algorithm is an algorithm to extract local features. The algorithm finds the extreme points in the scale space and then obtains the characteristics of scale, rotation invariant and position according to the extreme point.)