Extract external contour or silhouette of image in Python

Question

I want to extract the silhouette of an image, and I'm trying to do it using the contour function of MatplotLib. This is my code:

from PIL import Image
from pylab import *

# read image to array
im = array(Image.open('HOJA.jpg').convert('L'))

# create a new figure
figure()

# show contours with origin upper left corner
contour(im, origin='image')
axis('equal')

show()

This is my original image:

And this is my result:

But I just want to show the external contour, the silhouette. Just the read lines in this example.

How can I do it? I read the documentation of the contour function, but I can't get what I want.

If you know a better way to do this in Python, please tell me! (MatplotLib, OpenCV, etc.)

Answer 1

For those who want the OpenCV solution, here it is:

ret,thresh = cv2.threshold(image,245,255,0)
contours, hierarchy = cv2.findContours(thresh,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_NONE)

tam = 0

for contorno in contours:
    if len(contorno) > tam:
        contornoGrande = contorno
        tam = len(contorno)

cv2.drawContours(image,contornoGrande.astype('int'),-1,(0,255,0),2)

cv2.imshow('My image',image)

cv2.waitKey()
cv2.destroyAllWindows()

In this example, I only draw the biggest contour. Remember that 'image' must be a single-channel array.

You should change the parameters of the threshold function, the findContours function and the drawContours function to get what you want.

• threshold Documentation
• findContours Documentation
• drawContours Documentation

I do the conversion to 'int' in the drawContours function because there is a bug in the Open CV 2.4.3 version, and if you don't do this conversion, the program breaks. This is the bug.