get convex hull of an image

getConvexHull.py

#Original source from https://github.com/opencv/opencv/blob/master/samples/python/tutorial_code/ShapeDescriptors/hull/hull_demo.py

from __future__ import print_function
import cv2 as cv
import numpy as np
import argparse
import random as rng

rng.seed(12345)

def thresh_callback(val):
    threshold = val

    # Detect edges using Canny
    canny_output = cv.Canny(src_gray, threshold, threshold * 2)

    # Find contours
    contours, _ = cv.findContours(canny_output, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)

    # Find the convex hull object for each contour
    hull_list = []
    contourArea_list=[]
    maxHull=[]
    for i in range(len(contours)):
#     print(type(contours))
#     for index,i in enumerate(contours):
#         print(contours)
#         print(len(contours))
        hull = cv.convexHull(contours[i])
        area=cv.contourArea(hull)
        contourArea_list.append(area)
        hull_list.append(hull)
    
    print(max(contourArea_list))
#     print(contourArea_list.index(max(contourArea_list)))
#     print(hull_list[contourArea_list.index(max(contourArea_list))])
    maxHull.append(hull_list[contourArea_list.index(max(contourArea_list))])
#     print(maxHull[0])
#     print(hull_list[343])

    # Draw contours + hull results
    drawing = np.zeros((canny_output.shape[0], canny_output.shape[1], 3), dtype=np.uint8)
    for i in range(len(contours)):
        color = (rng.randint(0,256), rng.randint(0,256), rng.randint(0,256))
        cv.drawContours(drawing, contours, i, color)
#         cv.drawContours(drawing, hull_list, i, color)
    for i in range(len(maxHull)):
        cv.drawContours(drawing, maxHull, i, color)

    # Show in a window
    cv.imshow('Contours', drawing)

src = cv.imread("ic_sample.jpg")
if src is None:
    print('Could not open or find the image:', args.input)
    exit(0)

# Convert image to gray and blur it
src_gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)
src_gray = cv.blur(src_gray, (3,3))

# Create Window
source_window = 'Source'
cv.namedWindow(source_window)
cv.imshow(source_window, src)
max_thresh = 255
# thresh = 100 # initial threshold
thresh = 96 # initial threshold
cv.createTrackbar('Canny thresh:', source_window, thresh, max_thresh, thresh_callback)
thresh_callback(thresh)

cv.waitKey()