sift

说明：  经典的SIFT算法，第一步，选择感兴趣的点；第二步，对感兴趣点进行筛选，确定关键点；第三步，为关键点分配方向；第四步，用多维向量的形式描述关键点(Classical SIFT algorithm, the first step, select the point of interest second step, points of interest were screened to identify key points the third step, the key point for the distribution of direction The fourth step is described with the key in the form of multi-dimensional vector point)