How to create polygons for watershed segmentation

Question

I have an image and would like to create polygons of segments this image using marker-controlled watershed. I wrote the following code but I can't separate objects attached each other and create the polygons of the object.

How can solve those issues? Thanks so much for your help.

import cv2
import numpy as np
import scipy.misc
import scipy.ndimage as snd
# image is read and is converted to a numpy array
img = cv2.imread('D:/exam_watershed/Example_2_medicine/Medicine_create_poly/medicine.jpg')
# image is convereted to grayscale
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
# binary thresholding is done using the threshold
# from Otsu's method
ret1,thresh1 = cv2.threshold(gray,0,255,cv2.THRESH_BINARY+cv2.THRESH_OTSU)
# foreground pixels are determined by
# performing erosion
fore_ground = cv2.erode(thresh1,None,iterations = 3)
bgt = cv2.dilate(thresh1,None,iterations = 3)
ret,back_ground = cv2.threshold(bgt,1,100,1)
# marker is determined by adding foreground and background pixels
marker = cv2.add(fore_ground,back_ground)
# converting marker to 32 int
marker32 = np.int32(marker)
cv2.watershed(img,marker32)
res = scipy.misc.toimage(marker32)
res.save('D:/exam_watershed/Example_2_medicine/Medicine_create_poly/res_output.png')

Answer 1

This question seems to be pretty close to your needs, since the example uses the exact same image as yours.

To transform the resulting "dams" into polygons, I suggest using cv2.findContours together with cv2.approxPolyDP on the result image.