I was trying to draw contours in an image using Python OpenCV. My code is the following: I am getting an error while compiling this code. The error is the following: How can I avoid this error? Answer The problem should be that cv2.drawContours (and in general all opencv "drawing" functions in python) have output equal to None. Try this

Python showing an OpenCV Assertion error for finding contours

I was trying to draw contours in an image using Python OpenCV. My code is the following:

import numpy as np
import cv2
import Image
a = cv2.imread('train.jpg')
b = cv2.cvtColor(a, cv2.COLOR_BGR2GRAY)
ret, c = cv2.threshold(b, 127, 255, cv2.THRESH_BINARY)
contours, h = cv2.findContours(c, 1, 2) 
d = cv2.drawContours(a, contours, -1, (128, 255, 0), 1)
cv2.imshow('abs', d)
cv2.waitKey(0)

I am getting an error while compiling this code. The error is the following:

OpenCV Error: Assertion failed (size.width>0 && size.height>0) in imshow, file /home/travis/miniconda/conda-bld/work/opencv-2.4.11/modules/highgui/src/window.cpp, line 261
Traceback (most recent call last):
  File "shape.py", line 9, in <module>
    cv2.imshow('abs',d)
cv2.error: /home/travis/miniconda/conda-bld/work/opencv-2.4.11/modules/highgui/src/window.cpp:261: error: (-215) size.width>0 && size.height>0 in function imshow

How can I avoid this error?

Answer

The problem should be that cv2.drawContours (and in general all opencv “drawing” functions in python) have output equal to None. Try this way:

cv2.drawContours(a, contours, -1, (128, 255, 0), 1)
cv2.imshow('abs', a)
cv2.waitKey(0)

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Answer