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          


        

Answer 1

If you want to stick with your contour approach you can simply add a levels argument with a value 'thresholding' the image between the white background and the leaf.

You could use the histogram to find an appropriate value. But in this case any value slightly lower than 255 will do.

So:

contour(im, levels=[245], colors='black', origin='image')

Make sure you checkout Scikit-Image if you want to do some serious image processing. It contains several edge detection algoritms etc.

http://scikit-image.org/docs/dev/auto_examples/

Answer 2

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.

Answer 3

I would recommand using OpenCV for performance. It has a findContour functions accessible from python using the cv2 binding. This function can be set to return only the external contour.

You will have to threshold your image as well.