I am playing with openCV and doing simple below task.

1) Read Image

2) thresholding

3) Finding contours.

4) Drawing all contours in the blank image.

5) Drawing individual contour.

Drawing all contours on the dummy image looks good, whereas drawing single contour produces scattered contour as shown in the below images.

Original:

All Contours :

Single Contour :

Please find the code below.

import  cv2
import numpy as np

#Reading Image.
srcImg = cv2.imread("./bottle.jpeg")

#Color Conversion.

grayedImg = cv2.cvtColor(srcImg,cv2.COLOR_RGB2GRAY)
__, thresholdedImg = cv2.threshold(grayedImg, 240, 255, cv2.THRESH_BINARY)

#Noice Removal
kernel = cv2.getStructuringElement(cv2.MORPH_RECT, (3,3))
erodeImage = cv2.erode(thresholdedImg,kernel, iterations=1)
dilatedImg = cv2.dilate(erodeImage,kernel, iterations=1)
_, contours, _ = cv2.findContours(dilatedImg,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)

#draw All Contours.

dummyImg = np.zeros(grayedImg.shape, dtype=grayedImg.dtype)
cv2.drawContours(dummyImg, contours, -1, 255, 1)
cv2.imshow("All Contours", dummyImg)
cv2.imwrite("allContours.jpeg",dummyImg)

#draw Individual Contours.

mask =  np.zeros(dummyImg.shape[:2], dtype= dummyImg.dtype)
isolatedImg = cv2.drawContours(mask, contours[9], -1, 255, 1)

cv2.imshow("Indivial Contours.", isolatedImg)
cv2.imwrite("single.jpeg",isolatedImg)

cv2.waitKey(0)