Chessboard Camera Calibration using OpenCV

Question

I am trying to compute the distance of an object from the camera using stereo vision approach. But before computing the disparity map, I must ensure that my cameras are calibrated.

I followed the opencv python tutorial on camera calibration. They have used a chessboard to calibrate their cameras. Now my question is, if I want to calibrate my cameras, do I need to click photos of a chessboard from various angles manually? Or can I use the 14 chessboard images they have made available?

My next question (depending on the answer to the previous question) is, if I can use their images to calibrate my cameras, what is the logic behind this? How can images clicked from their cameras be used to calibrate my cameras, i.e. get the camera matrix for my cameras? I would like to get more intuition behind this camera calibration process.

Any help will be appreciated. Thanks.

Answer 1

1- No, you print something similar with a chessboard pattern and you use it to calibrate your own camera. You can use code at here.

2- The process basically goes like this: To determine coordinate of a pixel in an image, you need to know two(counting only most fundamental ones, currently I exclude distortion parameters) set of parameters. First set of parameters are inner parameters of your camera (intrinsic parameters) are optical center of your camera (basically center pixel of your sensor/lens) and focal length of your camera. Intrinsic parameters are fixed for your camera unless you change some settings of the device or some settings change with time. Second set of parameters are a position and rotation vector that describes where your camera is in the 3D world (these are extrinsic parameters). Extrinsic parameters change for every example image you have. You can think of camera calibration as an optimization process that tries to find best parameters (parameters that give minimum reprojection error) for the example images you have given.