Introduction to SIFT (Scale-Invariant Feature Transform)

SIFT OpenCV 官方文档：

https://docs.opencv.org/master/da/df5/tutorial_py_sift_intro.html

https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_feature2d/py_sift_intro/py_sift_intro.html

AttributeError: module 'cv2' has no attribute 'SIFT'

在用python使用opencv进行SIFT时候，编译出现这样问题：

Traceback (most recent call last):
  File "F:\image\test.py", line 7, in <module>
    sift = cv2.SIFT()

　　

出错代码如下：

import cv2
import numpy as np

img = cv2.imread('home.jpg')
gray= cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

sift = cv2.SIFT()
kp = sift.detect(gray,None)

img=cv2.drawKeypoints(gray,kp)

　　

原因：opencv将SIFT等算法整合到xfeatures2d集合里面了。变更后写法如下：

import cv2
import numpy as np

img = cv2.imread('home.jpg')
gray= cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

sift = cv2.xfeatures2d.SIFT_create()
kp = sift.detect(gray,None)

img=cv2.drawKeypoints(gray,kp)
cv2.imwrite('sift_keypoints.jpg',img)

　　

然后又出现错误：

Traceback (most recent call last):
  File "F:\image\test.py", line 7, in <module>
    sift = cv2.xfeatures2d.SIFT_create()
AttributeError: module 'cv2' has no attribute 'xfeatures2d'

　　

再尝试解决：

出错原因：

**原因：**3.X以后OpenCv只包含部分内容，需要神经网络或者其他的函数需要导入opencv_contrib

解决方法：

pip install opencv-contrib-python

注意： 
如果已经安装OpenCv2，则需要先卸载pip uninstall opencv-python再安装

参考资料：https://pypi.python.org/pypi/opencv-contrib-python

再次出错：

cv2.error: OpenCV(3.4.3) C:\projects\opencv-python\opencv_contrib\modules\xfeatures2d\src\sift.cpp:1207: 
error: (-213:The function/feature is not implemented) This algorithm is patented and is excluded in this configuration; 
Set OPENCV_ENABLE_NONFREE CMake option and rebuild the library in function 'cv::xfeatures2d::SIFT::create'