[Python] Why does the Harris corner detector can't detect finely corners of a chessboard?

I am trying to use Harris method for corner detection on a chessboard but the result i'm getting is not good:



In fact, I am facing the following problems:

• All the corners are not detected (see image attached).
• The dots that are marking the corners are not what I expected: I want these dots to be circular with one dot per detected corner.

You can find my code below.

import cv2 as cv
import numpy as np

file = chess.bmp
img = cv.imread(file)
img_gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
img_gray = np.float32(img_gray)

dst = cv.cornerHarris(img_gray, blockSize=2, ksize=3, k=0.02)

dst = cv.dilate(dst, None)

img[dst > 0.01 * dst.max()] = [0, 0, 255]

cv.imshow("Corner detection", img)
cv.waitKey()
cv.destroyAllWindows()

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