Create mask or boundary from each other in Python3

Question

I would like to get the mask from images with boundaries or boundaries from images of masks.

Here are two images:

I went through the followings, I did not understand the logic there: link1, link2, link3, link4

thanks, ilyas

Answer 1

I still do not understand the logic, however, one can create boundary from mask and mask from boundary.

import os
import numpy as np
import cv2
from matplotlib import pyplot as plt

out = "mask_boundary.png"
inp = "mask.png"
im = cv2.imread(inp)
imgray = cv2.cvtColor(im,cv2.COLOR_BGR2GRAY)
ret,thresh = cv2.threshold(imgray,127,255,0)
contours, hierarchy = cv2.findContours(thresh,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_NONE)
tmp = np.zeros_like(im)
boundary = cv2.drawContours(tmp, contours, -1, (255,255,255), 1)
plt.imsave(out, boundary, cmap = "gray")


out = "boundary_mask.png"
inp = "mask_boundary.png"
im = cv2.imread(inp)
imgray = cv2.cvtColor(im,cv2.COLOR_BGR2GRAY)
ret,thresh = cv2.threshold(imgray,0,255,0)
contours, hierarchy = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_NONE)
tmp = np.zeros_like(im)
boundary = cv2.drawContours(tmp, contours, 0,(255,255,255), -1)
for i in range(1,len(contours)):
    boundary = cv2.drawContours(boundary, contours, i,(255,255,255), -1)

plt.imsave(out, boundary, cmap = "gray")



out = "boun_mask.png"
inp = "boundary.png"
im = cv2.imread(inp)
imgray = cv2.cvtColor(im,cv2.COLOR_BGR2GRAY)
ret,thresh = cv2.threshold(imgray,0,255,0)
contours, hierarchy = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_NONE)
tmp = np.zeros_like(im)
boundary = cv2.drawContours(tmp, contours, 0,(255,255,255), -1)
for i in range(1,len(contours)):
    boundary = cv2.drawContours(boundary, contours, i,(255,255,255), -1)

plt.imsave(out, boundary, cmap = "gray")

Note: using the mask image above, I first created boundary and then from this boundary I created mask. However, I could not convert all boundary above to mask, especially the one at the image edges/border. It looks like there must be boundary at the border as well! Any help on that will be appreciated!

convert the above mask to boundary:

now convert the new boundary to mask:

now convert the above boundary to mask: