getting error in canny edge detection

Question

i am trying to write a code using opencv python that automatically get canny threshold values instead of doing them manually every time.

img= cv2.imread('micro.png',0)
output = np.zeros(img.shape, img.dtype)
# Otsu's thresholding
ret2,highthresh = cv2.threshold(img,0,255,cv2.THRESH_BINARY+cv2.THRESH_OTSU)
lowthresh=0.1*highthres
edges = cv2.Canny(img,output,lowthresh,highthresh)
cv2.imshow('canny',edges)

i am getting this error "File "test2.py", line 14, in edges = cv2.Canny(img,output,lowthresh,highthresh) TypeError: only length-1 arrays can be converted to Python scalars"

can anyone help me to sort out this error.thankx in advance

I think it has problem with png file, I also get the same error. try converting the image to JPG — Akshay
– Akshay, Commented Jan 23, 2017 at 23:31

Andrew Johnson · Accepted Answer · 2014-07-22 20:11:58Z

2

It seems like cv2.threshold returns the detected edges, and Canny applies them to the image. The code below worked for me and gave me some nice detected edges in my image.

import cv2

cv2.namedWindow('canny demo')

img= cv2.imread('micro.png',0)
ret2,detected_edges = cv2.threshold(img,0,255,cv2.THRESH_BINARY+cv2.THRESH_OTSU)
edges = cv2.Canny(detected_edges,0.1,1.0)
dst = cv2.bitwise_and(img,img,mask = edges)
cv2.imshow('canny',dst)

if cv2.waitKey(0) == 27:
    cv2.destroyAllWindows()

answered Jul 22, 2014 at 20:11

Andrew Johnson

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user3778289 Over a year ago

this is not giving me the require output.and i have to work on more then one pictures thats why i can't set threshold values everytime for that i got the concept from here. stackoverflow.com/questions/4292249/…. but it is not working for me

Emile Bergeron · Accepted Answer · 2016-10-24 03:57:04Z

1

You are running:

cv2.Canny(img,output,lowthresh,highthresh)

It is looking for

cv2.Canny(img,lowthresh,highthresh,output)

I think the ordering changed in some version, because I have seen references to both.

edited Oct 24, 2016 at 3:57

Emile Bergeron

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answered Oct 23, 2016 at 17:44

Shane

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