OpenCV with Python By Example

1. import cv2
   
2. import numpy as np
   
3. 
   
4. face_cascade = cv2.CascadeClassifier('cascade_files/haarcascade_frontalface_alt.xml')
   
5. 
   
6. if face_cascade.empty():
   
7.         raise IOError('Unable to load the face cascade classifier xml file')
   
8. 
   
9. cap = cv2.VideoCapture(0)
   
10. scaling_factor = 0.5
    
11. 
    
12. while True:
    
13.     ret, frame = cap.read()
    
14.     frame = cv2.resize(frame, None, fx=scaling_factor, fy=scaling_factor, interpolation=cv2.INTER_AREA)
    
15.     gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    
16. 
    
17.     face_rects = face_cascade.detectMultiScale(gray, 1.3, 5)
    
18.     for (x,y,w,h) in face_rects:
    
19.         cv2.rectangle(frame, (x,y), (x+w,y+h), (0,255,0), 3)
    
20. 
    
21.     cv2.imshow('Face Detector', frame)
    
22. 
    
23.     c = cv2.waitKey(1)
    
24.     if c == 27:
    
25.         break
    
26. 
    
27. cap.release()
    
28. cv2.destroyAllWindows()

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1. import cv2
   
2. import numpy as np
   
3. 
   
4. gray_image = cv2.imread('../images/input_brief.jpg', 0)
   
5. 
   
6. # Initiate FAST detector
   
7. fast = cv2.FastFeatureDetector()
   
8. 
   
9. # Initiate BRIEF extractor
   
10. brief = cv2.DescriptorExtractor_create("BRIEF")
    
11. 
    
12. # find the keypoints with STAR
    
13. keypoints = fast.detect(gray_image, None)
    
14. 
    
15. # compute the descriptors with BRIEF
    
16. keypoints, descriptors = brief.compute(gray_image, keypoints)
    
17. 
    
18. gray_keypoints = cv2.drawKeypoints(gray_image, keypoints, color=(0,255,0))
    
19. cv2.imshow('BRIEF keypoints', gray_keypoints)
    
20. cv2.waitKey()

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