System Information

opencv-python-headless==4.9.0.80
Operating System / Platform: Ubuntu 22.04 in docker
Python version: 3.11.9

Detailed description

ploting a square with square hole:

using this code:

    # Create a binary mask with several polygons, some with holes
    im = np.zeros((100, 100), dtype=np.uint8)

    # Polygon (square with a hole)
    im[30:50, 30:50] = 1
    im[35:45, 35:45] = 0
    fig, ax = plt.subplots()
    plt.imshow(im)
    plt.show()

    contours_tuple_of_Nx1x2_uv_arrays, hierarchy_1xNx4 = cv2.findContours(im, cv2.RETR_CCOMP, cv2.CHAIN_APPROX_SIMPLE)
    for x in contours_tuple_of_Nx1x2_uv_arrays:
        print(x.shape)
# result of print:
# (4, 1, 2)
# (8, 1, 2)

running this will give us the inner hole contour with bad corners - as you can see the inner hole should be square but we get 8 points in the contour and it looks like this:

Steps to reproduce

above

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues, forum.opencv.org, Stack Overflow, etc and have not found any solution
• I updated to the latest OpenCV version and the issue is still there
• There is reproducer code and related data files (videos, images, onnx, etc)