filling contours with opencv python

Question

I have binary image with polylines created with:

cv2.polylines(binaryImage,contours,1, (255,255,255))

What I need now is effective method t

Answer 1

You can use fillPoly or drawContours if your contour is closed. Pulling together @jabaldonedo and @ash-ketchum answers:

import cv2
import matplotlib.pyplot as plt
import numpy as np

# Lets first create a contour to use in example
cir = np.zeros((255,255))
cv2.circle(cir,(128,128),10,1)
_, contours, _ = cv2.findContours(cir.astype(np.uint8), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)

# An open circle; the points are in contours[0]
plt.figure()
plt.imshow(cir)

# Option 1: Using fillPoly
img_pl = np.zeros((255,255))
cv2.fillPoly(img_pl,pts=contours,color=(255,255,255))
plt.figure()
plt.imshow(img_pl)

# Option 2: Using drawContours
img_c = np.zeros((255,255))
cv2.drawContours(img_c, contours, contourIdx=-1, color=(255,255,255),thickness=-1)
plt.figure()
plt.imshow(img_c)

plt.show()

both img_pl and img_c contain a filled in circle from the points in contour[0]

Answer 2

I think what you are looking for is cv2.fillPoly, which fills the area bounded by one or more polygons. This is a simple snippet, I generate a contour of four points representing vertices of a square, then I fill the polygon with a white color.

import numpy as np
import cv2

contours = np.array( [ [50,50], [50,150], [150, 150], [150,50] ] )
img = np.zeros( (200,200) ) # create a single channel 200x200 pixel black image 
cv2.fillPoly(img, pts =[contours], color=(255,255,255))
cv2.imshow(" ", img)
cv2.waitKey()

Answer 3

While using cv2.drawContours function, set thickness=cv2.FILLED and you are done.