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opencvimage-processingsiftkeypoint

OpenCV - Display ONLY the keypoints NOT the image using SIFT

I am trying to only draw the keypoints (without the image) using this example code:

import cv2
import numpy as np

img = cv2.imread('test.png')
gray= cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

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

img=cv2.drawKeypoints(gray,kp)

cv2.imwrite('sift_keypoints.jpg',img)

I tried cv2.drawKeypoints(None,kp)and cv2.drawKeypoints(kp) but to no avail.

Any ideas how this could be achieved ?

Thanks.

Solution

  • You can get ONLY the keypoints by drawing them on a solid black image having the SAME shape of your original image.

    This is the image I used:

    enter image description here

    I then obtained the keypoints:

    enter image description here

    Then I created an image of solid color(black) having same size of the original image and draw these keypoints on them.

    enter image description here

    Voila ONLY keypoints

    CODE:

    #---Creating image of solid color with same size as image---
mask = np.zeros((img.shape[0], img.shape[1], 3), np.uint8)
mask[:] = (0, 0, 0) 

#---Drawing keypoints on the mask image---
fmask = cv2.drawKeypoints(mask,kp,None,color=(0,255,0), flags=0)
cv2.imshow('fmask.jpg', fmask)