參考地址：https://docs.opencv.org/3.4/d2/d29/classcv_1_1KeyPoint.html

測試程式碼：

import cv2  
import numpy as np  
  
img = cv2.imread('4.jpg',cv2.IMREAD_COLOR)  
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)  
# cv2.imshow('origin',img)
  
#SIFT  
detector = cv2.xfeatures2d.SIFT_create()
keypoints = detector.detect(gray,None)  
cv2.drawKeypoints(gray,keypoints,img)  

points2f 
 
= cv2.KeyPoint_convert(keypoints)  #將KeyPoint格式資料中的xy座標提取出來。
print(keypoints)
print(points2f)

cv2.imshow('test',img)

cv2.waitKey(0)  
cv2.destroyAllWindows() 

測試效果：