How to do it...

1. Import the modules:

import cv2
import matplotlib.pyplot as plt

2. Load the test image with a chessboard:

image_chess = cv2.imread('../data/chessboard.png')

3. Detect the chessboard pattern:

found, corners = cv2.findChessboardCorners(image_chess, (6, 9))
assert found == True, "can't find chessboard pattern"

4. Draw the detected pattern:

dbg_image_chess = image_chess.copy()
cv2.drawChessboardCorners(dbg_image_chess, (6, 9), corners, found);

5. Load the test image with a circle grid pattern:

image_circles = cv2.imread('../data/circlesgrid.png')

6. Detect the circle grid pattern:

found, corners = cv2.findCirclesGrid(image_circles, (6, 6), cv2.CALIB_CB_SYMMETRIC_GRID)
assert found == True, "can't find circles grid pattern"

7. Draw the detected pattern:

dbg_image_circles = image_circles.copy()
cv2.drawChessboardCorners(dbg_image_circles, (6, 6), corners, found);

8. Visualize the results:

plt.figure(figsize=(8,8))
plt.subplot(221)
plt.title('original')
plt.axis('off')
plt.imshow(image_chess)
plt.subplot(222)
plt.title('detected pattern')
plt.axis('off')
plt.imshow(dbg_image_chess)
plt.show()
plt.subplot(223)
plt.title('original')
plt.axis('off')
plt.imshow(image_circles)
plt.subplot(224)
plt.title('detected pattern')
plt.axis('off')
plt.imshow(dbg_image_circles)
plt.tight_layout()
plt.show()