CODEWITHSUNDEEP
pythonopencvimage-processingcomputer-visioncontour
learner
learner

Reputation: 2752

opencv - plot contours in an image

I am trying to draw contour around an image. I can see that contours being found but I am not able to draw the outline. The color of the contour seem to be either of the two (black and white) colors. 

import cv2
import numpy as np
import matplotlib.pyplot as plt
from skimage import io
%matplotlib inline
im = io.imread('http://matlabtricks.com/images/post-35/man.png')
plt.imshow(im)
imgray = cv2.cvtColor(im,cv2.COLOR_BGR2GRAY)
plt.figure()
plt.imshow(imgray)

#Contoured image
ret,thresh = cv2.threshold(imgray, 120,255,cv2.THRESH_BINARY)
image, contours, hierarchy = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
c_img = cv2.drawContours(image, contours, -1, (0, 255, 0), 1)
plt.figure()
plt.imshow(c_img)

Upvotes: 5

Views: 23495

Answers (2)

Sandipan Dey
Sandipan Dey

Reputation: 23129

You need to draw on the original image, not on the one returned from findContuors(). The following works.

# Contoured image
ret,thresh = cv2.threshold(imgray, 120,255,cv2.THRESH_BINARY)
contours = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)[-2]
for contour in contours:
   cv2.drawContours(im, contour, -1, (0, 255, 0), 3)
plt.figure()
plt.imshow(im)

enter image description here

Upvotes: 12

Kinght 金
Kinght 金

Reputation: 18341

This is my result:

enter image description here

## Read and convert 
img = io.imread('http://matlabtricks.com/images/post-35/man.png')
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

## Find outer contours 
_, cnts, _= cv2.findContours(gray,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)

## Draw 
canvas = np.zeros_like(img)
cv2.drawContours(canvas , contours, -1, (0, 255, 0), 1)

plt.imshow(canvas)

Upvotes: 10

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