[Python] opencv cv2.drawcontours contour argument: contour vs [contour]

my input :



my code :

# import the necessary packages
import numpy as np
import argparse
import imutils
import cv2


print("Your OpenCV version: {}".format(cv2.__version__))
print("Are you using OpenCV 2.X? {}".format(imutils.is_cv2()))
print("Are you using OpenCV 3.X? {}".format(imutils.is_cv3()))
print("Are you using OpenCV 4.X? {}".format(imutils.is_cv4()))


# load the image
image_orig = cv2.imread('box1.jpg')
height_orig, width_orig = image_orig.shape[:2]

# cv2.imshow('image_orig' , image_orig)
# cv2.waitKey(0)
cv2.imwrite('image_orig.png', image_orig)


# copy of original image
image_to_process = image_orig.copy()

image_gray = cv2.cvtColor(image_to_process, cv2.COLOR_BGR2GRAY)
image_gray = cv2.GaussianBlur(image_gray, (5, 5), 0)


# cv2.imshow('image_gray' , image_gray)
# cv2.waitKey(0)
cv2.imwrite('image_gray.png', image_gray)

# perform edge detection, then perform a dilation + erosion to close gaps in between object edges
image_edged = cv2.Canny(image_gray, 50, 100)
image_edged = cv2.dilate(image_edged, None, iterations=1)
image_edged = cv2.erode(image_edged, None, iterations=1)

# cv2.imshow('image_edged' , image_edged)
# cv2.waitKey(0)
cv2.imwrite('image_edged.png', image_edged)


# find contours in the edge map
cnts = cv2.findContours(image_edged, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)

cnts = cnts[1] if imutils.is_cv2() else cnts[0] #### #### using CV4

print(len(cnts))



# loop over the contours individually

# prints contours in red color thickness = 1
image_contours = image_to_process.copy()
for c in cnts:

cv2.drawContours(image_contours, c , -1 ,(0,0,255),1)

cv2.imshow('1', image_contours)
cv2.waitKey(0)



# prints contours in red color thickness = 10
image_contours = image_to_process.copy()
for c in cnts:

cv2.drawContours(image_contours, c , -1 ,(0,0,255),10)

cv2.imshow('10', image_contours)
cv2.waitKey(0)

# prints contours in red color thickness = cv2.FILLED
image_contours = image_to_process.copy()
for c in cnts:

cv2.drawContours(image_contours, c , -1 ,(0,0,255), cv2.FILLED)

cv2.imshow('filled', image_contours)
cv2.waitKey(0)

# prints contours in red color thickness = cv2.FILLED
image_contours = image_to_process.copy()
for c in cnts:

cv2.drawContours(image_contours, [c] , -1 ,(0,0,255), cv2.FILLED)

cv2.imshow('filled_[]', image_contours)
cv2.waitKey(0)


output:



Any particular reason:

cv2.drawContours(image_contours, [c] , -1 ,(0,0,255), cv2.FILLED)

works while

cv2.drawContours(image_contours, c , -1 ,(0,0,255), cv2.FILLED)

doesn't , and why

cv2.drawContours(image_contours, c , -1 ,(0,0,255), 10) do work ?

Which one is the right way to code it ? Am I missing anything ?

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