ChArUco calibration board generator
A ChArUco board is the target most camera calibrations should use. It is a chessboard with an ArUco marker in every white square, so the corners are accurate and the markers say which corner is which.
Open the generator with this board
Why calibrate with ChArUco
A chessboard corner can be located to a fraction of a pixel, because four regions meet at one point. A marker corner cannot. Calibration fits a camera model to those points, so the accuracy of the points sets the accuracy of the result.
The markers let the board be found when it is partly outside the frame, which a plain chessboard cannot do. That matters, because a good calibration needs the target near the edges and corners of the image where distortion is strongest.
Choosing the numbers
Give the board a different number of squares across and down, so it cannot be read at the wrong rotation. Five by seven or seven by nine are good shapes.
The marker should be about three quarters of the square. Too large and the white edge around it disappears; too small and the marker loses range.
Make the board as large as the sheet allows. A larger board fills more of the image at a workable distance, and the calibration improves.
Taking the pictures
Take twenty to forty frames. Cover the whole image area, especially the corners, and vary the angle by thirty to forty five degrees in both directions. Frames taken straight on carry very little information about the lens.
Keep the board still and the exposure short. A blurred corner is worse than no corner.