CODEWITHSUNDEEP
opencvpython-2.7
Edgar H
Edgar H

Reputation: 1518

Opencv: cv2.findContours modifies image that has already been plotted?

I'm encountering a odd behaviour and while I can work around it I would like to know why this is.

When I use cv2.findContours it modifies the original image, even if I haven't passed it to the function. Here is a minimal example where the picture can be found here. 

import matplotlib.pyplot as plt
import cv2

img =cv2.imread('a.jpg',0)
a1=plt.subplot(121)
plt.imshow(img, cmap='Greys')

ret, thresh = cv2.threshold(img,57,255,cv2.THRESH_BINARY)

a1=plt.subplot(122)
plt.imshow(thresh, cmap='Greys')
plt.show()

temp=thresh
del thresh

contours, hierarchy = cv2.findContours(temp,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)

When I comment out the line with cv2.findContours it works fine. Why is that?

Upvotes: 0

Views: 1989

Answers (1)

smeso
smeso

Reputation: 4295

It happens because temp is thresh. In python when you make an assignment like that you are not coping the object, you are just making a new reference. Take a look at copy module to achieve your goal.

Upvotes: 2

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