ChArUco pattern has broken backward compatibility

[stefan523]

System Information

OpenCV version: 4.7.0

Detailed description

ChArUco patterns have been moved recently from OpenCV contrib to the main branch in OpenCV 4.7.0, but such patterns have been used for a longer time across the world. Backwards compatiblity with pre-existing targets and data needs to be ensured to avoid waste of resources and material.

OpenCV (contrib) 4.6.0 introduced a backwards incompatible change in ChArUco pattern generation for even row count. The impact is quite big.

• Existing calibration targets that have been self-manufactured or procured expensively are incompatible with the latest OpenCV versions.
• On stock targets from e.g. https://calib.io/ do not work with OpenCV anymore.
• Acquired calibration data images cannot be processed anymore.

Related issues in OpenCV contrib:

• CharucoBoard_create regression / incompatible patterns (only even row count) with 4.6.0 opencv_contrib#3291
• Function interpolateCornersCharuco misplace corners opencv_contrib#3301

A fix is available that enables support for pre and post 4.6.0 patterns.

• ChArUco pre460 pattern support via switch opencv_contrib#3305

Steps to reproduce

import cv2
aruco_dict = cv2.aruco.getPredefinedDictionary(cv2.aruco.DICT_5X5_1000)
charuco_board = cv2.aruco.CharucoBoard_create(
    squaresX = 5,
    squaresY = 4,
    squareLength = 4,
    markerLength = 3,
    dictionary = aruco_dict
)
img_board = charuco_board.draw((250,200), marginSize=0, borderBits=1)
cv2.imwrite('charuco_OpenCV-' + cv2.__version__ + '.png', img_board)

OpenCV 4.5.5:

OpenCV 4.6.0:

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)

[stefan523]

A pull request with a fix has been raised: #23153

[stefan523]

Code to reproduce with OpenCV 4.7.0 (slightly changed interface):

import cv2
aruco_dict = cv2.aruco.getPredefinedDictionary(cv2.aruco.DICT_5X5_1000)
charuco_board = cv2.aruco.CharucoBoard(
    size = [5, 4],
    squareLength = 4,
    markerLength = 3,
    dictionary = aruco_dict
)
img_board = charuco_board.generateImage((250,200), marginSize=0, borderBits=1)
cv2.imwrite('charuco_OpenCV-' + cv2.__version__ + '.png', img_board)

[stefan523]

Fix in #23153 was merged (thanks @asmorkalov!). Will be resolved in next OpenCV release 4.8.0.

[M-A-Robson]

This is still an issue in 4.8.0.74

calib.io target:

python generated target:

aruco_dict = aruco.getPredefinedDictionary(aruco.DICT_4X4_250)
board = aruco.CharucoBoard((5, 4), 0.015, 0.012, aruco_dict)
imboard = board.generateImage((10000, 10000))

[gmedan]

You need to add board.setLegacyPattern(True)

[M-A-Robson]

Thank you @gmedan I had missed that. Here is a code snippet for those coming across this at a later date:

aruco_dict = aruco.getPredefinedDictionary(aruco.DICT_4X4_250)
board = aruco.CharucoBoard((5, 4), 0.015, 0.012, aruco_dict)
board.setLegacyPattern(True)
imboard = board.generateImage((10000, 10000))

result: