How to use cv2.fillpoly function properly [closed]

I am trying to use the fillpoly function to fill two polygons at once (with a triangle and a trapezium). Please find the below code.

# Import necessary libraries
import cv2
import numpy as np

# Read an image
img = np.zeros((500,500))

# Define an array of endpoints of triangle
points = np.array([[[160, 130], [350, 130], [250, 300]],[[160, 30], [50, 30], [80, 130],[100, 130]]],dtype=object)

# Use fillPoly() function and give input as
# image, end points,color of polygon
# Here color of polygon will blue
for i in range(len(points)):
    cv2.fillPoly(img, pts=[points[i]], color=(255, 0, 0))
#cv2.fillPoly(img, pts=[points[1]], color=(255, 0, 0))


# Displaying the image
cv2.imshow("Triangle", img)

# wait for the user to press any key to
# exit window
cv2.waitKey(0) 

# Closing all open windows
cv2.destroyAllWindows()

However, the output gives me an error. Please find it below.

/var/folders/hh/phtw2ldx7gj88krjgwdbz9680000gn/T/ipykernel_1755/1373141779.py:9: VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences (which is a list-or-tuple of lists-or-tuples-or ndarrays with different lengths or shapes) is deprecated. If you meant to do this, you must specify 'dtype=object' when creating the ndarray.
  points = np.array([[[160, 130], [350, 130], [250, 300]],[[160, 30], [50, 30], [80, 130],[100, 130]]])
---------------------------------------------------------------------------
error                                     Traceback (most recent call last)
Input In [35], in <cell line: 14>()
     11 # Use fillPoly() function and give input as
     12 # image, end points,color of polygon
     13 # Here color of polygon will blue
     14 for i in range(len(points)):
---> 15     cv2.fillPoly(img, pts=[points[i]], color=(255, 0, 0))
     16 #cv2.fillPoly(img, pts=[points[1]], color=(255, 0, 0))
     17 
     18 
     19 # Displaying the image
     20 cv2.imshow("Triangle", img)

error: OpenCV(4.6.0) :-1: error: (-5:Bad argument) in function 'fillPoly'
> Overload resolution failed:
>  - Can't parse 'pts'. Sequence item with index 0 has a wrong type
>  - Can't parse 'pts'. Sequence item with index 0 has a wrong type

It gives an error due to the different number in coordinates of the polygones (3 and 4 respectively).

Would anyone be able to help me in this regards please.

Thanks & Best Regards

Schroter Michael

Answer

1. Your image needs to have 3 channels (np.zeros((500, 500, 3))) instead of 1.
2. Your coordinates need to be np.int32.

import cv2
import numpy as np

img = np.zeros((500, 500, 3))

# Define an array of points.
points = [
    [[160, 130], [350, 130], [250, 300]],
    [[160, 30], [50, 30], [80, 130], [100, 130]],
]

for poly in points:
    cv2.fillPoly(img, np.array([poly], dtype=np.int32), (255, 0, 0))

# Displaying the image
cv2.imshow("Triangle", img)

# wait for the user to press any key to
# exit window
cv2.waitKey(0)

# Closing all open windows
cv2.destroyAllWindows()