Feature Detection

The SIFT & SURF algorithms are patented by their respective creators, and while they are free to use in academic and research settings, you should technically be obtaining a license/permission from the creators if you are using them in a commercial (i.e. for-profit) application.

SIFT

http://www.inf.fu-berlin.de/lehre/SS09/CV/uebungen/uebung09/SIFT.pdf



In [4]:

    
import cv2
import numpy as np

image = cv2.imread('images/input.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

#Create SIFT Feature Detector object
sift = cv2.SIFT()

#Detect key points
keypoints = sift.detect(gray, None)
print("Number of keypoints Detected: ", len(keypoints))

# Draw rich key points on input image
image = cv2.drawKeypoints(image, keypoints, flags=cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)

cv2.imshow('Feature Method - SIFT', image)
cv2.waitKey(0)
cv2.destroyAllWindows()









    



('Number of keypoints Detected: ', 1890)

SURF

http://www.vision.ee.ethz.ch/~surf/eccv06.pdf



In [7]:

    
import cv2
import numpy as np

image = cv2.imread('images/input.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

#Create SURF Feature Detector object
surf = cv2.SURF()

# Only features, whose hessian is larger than hessianThreshold are retained by the detector
surf.hessianThreshold = 500
keypoints, descriptors = surf.detectAndCompute(gray, None)
print "Number of keypoints Detected: ", len(keypoints)

# Draw rich key points on input image
image = cv2.drawKeypoints(image, keypoints, flags=cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)

cv2.imshow('Feature Method - SURF', image)
cv2.waitKey()
cv2.destroyAllWindows()









    



Number of keypoints Detected:  1543

FAST

https://www.edwardrosten.com/work/rosten_2006_machine.pdf http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/AV1011/AV1FeaturefromAcceleratedSegmentTest.pdf



In [8]:

    
import cv2
import numpy as np

image = cv2.imread('images/input.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

# Create FAST Detector object
fast = cv2.FastFeatureDetector()

# Obtain Key points, by default non max suppression is On
# to turn off set fast.setBool('nonmaxSuppression', False)
keypoints = fast.detect(gray, None)
print "Number of keypoints Detected: ", len(keypoints)

# Draw rich keypoints on input image
image = cv2.drawKeypoints(image, keypoints, flags=cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)

cv2.imshow('Feature Method - FAST', image)
cv2.waitKey()
cv2.destroyAllWindows()









    



Number of keypoints Detected:  8963

BRIEF

http://cvlabwww.epfl.ch/~lepetit/papers/calonder_pami11.pdf



In [9]:

    
import cv2
import numpy as np

image = cv2.imread('images/input.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

# Create FAST detector object
fast = cv2.FastFeatureDetector()

# Create BRIEF extractor object
brief = cv2.DescriptorExtractor_create("BRIEF")

# Determine key points
keypoints = fast.detect(gray, None)

# Obtain descriptors and new final keypoints using BRIEF
keypoints, descriptors = brief.compute(gray, keypoints)
print "Number of keypoints Detected: ", len(keypoints)

# Draw rich keypoints on input image
image = cv2.drawKeypoints(image, keypoints, flags=cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)
                                    
cv2.imshow('Feature Method - BRIEF', image)
cv2.waitKey()
cv2.destroyAllWindows()









    



Number of keypoints Detected:  8738

Oriented FAST and Rotated BRIEF (ORB)

http://www.willowgarage.com/sites/default/files/orb_final.pdf



In [17]:

    
import cv2
import numpy as np

image = cv2.imread('images/input.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

# Create ORB object, we can specify the number of key points we desire
orb = cv2.ORB()

# Determine key points
keypoints = orb.detect(gray, None)

# Obtain the descriptors
keypoints, descriptors = orb.compute(gray, keypoints)
print("Number of keypoints Detected: ", len(keypoints))

# Draw rich keypoints on input image
image = cv2.drawKeypoints(image, keypoints,flags=cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)

cv2.imshow('Feature Method - ORB', image)
cv2.waitKey()
cv2.destroyAllWindows()









    



('Number of keypoints Detected: ', 500)



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