Camera calibration issue estimating camera intrinsic parameters

[LucaDAmbrosio]

Hi Nicolai,
I am trying to use the code you provide in CameraCalibration.py to carry out a single camera calibration using a chessboard (7x9, 20mm square, frameSize = 640x480).
I use the RGB channel of an Intel D455, in order to use the real camera intrinics parameters and distortion coefficients as reference, from the methods directly provided by Realsense.
However, extracting camera intrinsics parameters and distortion coefficients, I get values which differs from the one provided by Realsense:

Python	       Realsense

fx 379.19 379.0404
fy 380.327 379.575531
cx 226.9 230.311981
cy 326.31 322.188538
d1 0.00053418 -0.058406677
d2 0.0016563 0.071961016
d3 0.00030966 -0.000692392
d4 0.00017886 -0.000478269
d5 -0.001937583 -0.022303361

These are the images used

However, the results regarding the camera's intrinsic parameters and distortion coefficients vary significantly each time I capture new images, making the captures unrepeatable.

Is there something that I am missing in carrying out the calibration procedure? Have you any suggestion to handle this issue?

I take this opportunity to thank you for all the content you create and for the examples you provide with your videos!
Best regards,

Luca D'Ambrosio