Introduction - If you have any usage issues, please Google them yourself
SIFT算法大致有四个步骤：
SIFT algorithm has four steps:
1，尺度空间极值检测。在尺度空间通过高斯微分函数来检测潜在的对于尺度和旋转不变的兴趣点。
1, the scale space extrema detection. In the scale space by Gauss differential function to detect potential for rotation and scale invariant interest point.
2，关键点定位。在兴趣点位置上，确定关键点的位置和尺度。
2, the key point positioning. At the point of interest position, to determine the location and scale of key points.
3，方向确定。基于图像局部的梯度方向，给每个关键点分配方向。
3, to determine the direction of. Local image based on gradient direction, for each of the key point distribution direction.
4，关键点描述。在每个关键点的领域内测量图像局部的梯度。最终用一个特征向量来表达。
4, the key point description. Measurement of gradient image part in each of the key points in the field. Finally expressed as a feature vector.