Charuco camera calibration with opencv 4.10

Question

I need to calibrate a camera with openCV and python.

My script can't find a match point. To simplify things, I'm using the Charuco pattern (with margin of white pixels) as my input image. Even so, no points are found. Here's the basic self-sufficient script.

import cv2
import numpy as np

aruco_dict = cv2.aruco.getPredefinedDictionary(cv2.aruco.DICT_4X4_50)
board = cv2.aruco.CharucoBoard((5, 7),0.01, 0.008, aruco_dict)
board.setLegacyPattern(True)

b = board.generateImage((200,200),marginSize = 20)

#image = cv2.imread('charuco_board.png')
#gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
gray = b
# first detection
aruco_detector = cv2.aruco.ArucoDetector(aruco_dict)
marker_corners, marker_ids, rejected_candidates = aruco_detector.detectMarkers(image)
print(marker_corners)
# refine
if marker_ids is not None:
    charuco_params = cv2.aruco.CharucoParameters()
    charuco_detector = cv2.aruco.CharucoDetector(board, charuco_params)
    charuco_corners, charuco_ids, _ = charuco_detector.detectBoard(gray, marker_corners, marker_ids)

    image_copy = image.copy()
    image_markers = cv2.aruco.drawDetectedMarkers(image_copy, marker_corners, marker_ids)
    image_charuco = cv2.aruco.drawDetectedCornersCharuco(image_markers, charuco_corners, charuco_ids)

    cv2.imshow('Detected ChArUco Corners', image_charuco)
    cv2.waitKey(0)
    cv2.destroyAllWindows()
else:
    print("No corners detected.")

Edit : it seams that aruco 4X4_50 is broken. Working script :

import cv2
import numpy as np

aruco_dict = cv2.aruco.getPredefinedDictionary(cv2.aruco.DICT_6X6_250)
board = cv2.aruco.CharucoBoard((5, 7),0.01, 0.008, aruco_dict)
board.setLegacyPattern(True)

b = board.generateImage((2000,2000),marginSize = 20)
cv2.imwrite('charuco_board.png',b)
gray = b
# first detection
aruco_detector = cv2.aruco.ArucoDetector(aruco_dict)
marker_corners, marker_ids, rejected_candidates = aruco_detector.detectMarkers(b)
print(marker_corners)
# refine
if marker_ids is not None:
    charuco_params = cv2.aruco.CharucoParameters()
    charuco_detector = cv2.aruco.CharucoDetector(board, charuco_params)
    #charuco_corners, charuco_ids, markerCorners, markerIds = charuco_detector.detectBoard(gray, marker_corners, marker_ids)
    charuco_corners, charuco_ids, markerCorners, markerIds = charuco_detector.detectBoard(gray)
    image_copy = b.copy()
    image_markers = cv2.aruco.drawDetectedMarkers(image_copy, marker_corners, marker_ids)
    image_charuco = cv2.aruco.drawDetectedCornersCharuco(image_markers, charuco_corners, charuco_ids)

    cv2.imshow('Detected ChArUco Corners', image_charuco)
    cv2.waitKey(0)
    cv2.destroyAllWindows()
else:
    print("No corners detected.")