Get area within contours Opencv Python?

Question

I have used an adaptive thresholding technique to create a picture like the one below:

Answer 1

A simple approach would be to close the holes in the foreground to form a single contour with cv2.morphologyEx() and cv2.MORPH_CLOSE

Now that the external contour is filled, we can find the outer contour with cv2.findContours() and use cv2.fillPoly() to fill in all pixels with white

import cv2

# Load in image, convert to grayscale, and threshold
image = cv2.imread('1.png')
gray = cv2.cvtColor(image,cv2.COLOR_BGR2GRAY)
thresh = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)[1]

# Close contour
kernel = cv2.getStructuringElement(cv2.MORPH_RECT, (7,7))
close = cv2.morphologyEx(thresh, cv2.MORPH_CLOSE, kernel, iterations=1)

# Find outer contour and fill with white
cnts = cv2.findContours(close, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
cnts = cnts[0] if len(cnts) == 2 else cnts[1]
cv2.fillPoly(close, cnts, [255,255,255])

cv2.imshow('close', close)
cv2.waitKey()