说明：  sift的详细介绍，主要步骤是：1.关键点检测2.关键点描述 3.关键点匹配 4.消除错配点。物体识别的必备资料
(sift the details, the main steps are: 1. The key point detection (2) describe key 3 key match 4 to eliminate the mismatch point. Essential information on object recognition)