missing required argument 'outImage' (pos 3)

Question

I am new to opencv and python. I tried with a sample code to extract the features of an image and I am getting this error:

TypeError: drawKeypoints() missing required argument 'outImage' (pos 3)

and my code goes like this

import numpy as np
import cv2
from matplotlib import pyplot as plt
img = cv2.imread('1.png',0)

fast = cv2.FastFeatureDetector_create()

kp = fast.detect(img,None)
img2 = cv2.drawKeypoints(img, kp, color=(255,0,0))

print ("Threshold: ", fast.getInt('threshold'))
print ("nonmaxSuppression: ", fast.getBool('nonmaxSuppression'))
print ("neighborhood: ", fast.getInt('type'))
print ("Total Keypoints with nonmaxSuppression: ", len(kp))
cv2.imwrite('fast_true.png',img2)

fast.setBool('nonmaxSuppression',0)
kp = fast.detect(img,None)
print ("Total Keypoints without nonmaxSuppression: ", len(kp))
img3 = cv2.drawKeypoints(img, kp, color=(255,0,0))
cv2.imwrite('fast_false.png',img3)

Want to see the extracted features of an image.

Any suggestions on how to extract the features of an image to compare with webcam image will be helpful.

Thanks.

Answer 1

It seems to be a bug in drawKeypoints() function. Its possible to assign outImage = None to solve it as:

img2 = cv2.drawKeypoints(img, kp, outImage = None, color=(255,0,0))

or create img2 and modify it inplace as:

img2 = cv2.merge([img, img, img])
cv2.drawKeypoints(img, kp, outImage = img2, color = (255, 0, 0), 
                    flags = cv2.DRAW_MATCHES_FLAGS_DRAW_OVER_OUTIMG)

Answer 2

I had the same problem and found that the problem was already solved here:

OpenCV can't draw keypoints

I tried the suggestion from the previous solution, this code works:

cv2.drawKeypoints(img, kp, outImage=img2, color=(255,0,0))

For your reference, if you look at the output from help for this procedure

help(cv2.drawKeypoints)

drawKeypoints(...)
    drawKeypoints(image, keypoints, outImage[, color[, flags]]) -> outImage

you will see that the output image (outImage) that is returned is contained in the parameters of the function call