Let's say I have chessboard images of size w(width) and h(height). (Notice that w and h are not the actual size of the chessboard but that of the images of chessboard.)

After (Zhang's) camera calibration, the resulted intrinsic camera parameters are fx(focal length x), fy(focal length y), cx(principal point x), cy(principal point y), k1(1st distortion factor), k2(2nd distortion factor), k3(3rd distortion factor), k4(4th distortion factor), k5(5th distortion factor).

If I resize the chessboard images by half so that the width and height of the resized images are w/2 and h/2 respectively and conduct camera calibration again, I would expect to theoretically get fx/2 ,fy/2, cx/2 and cy/2 as focal length x, focal length y, principal point x and principal point y respectively.

How about distortion factors ? What would I expect to get theoretically the 1st, 2nd, 3rd, 4th and 5th distortion factors of the resized chessboard images in terms of k1, k2, k3, k4 and k5 ?

After (Zhang's) camera calibration, the resulted intrinsic camera parameters are fx(focal length x), fy(focal length y), cx(principal point x), cy(principal point y), k1(1st distortion factor), k2(2nd distortion factor), k3(3rd distortion factor), k4(4th distortion factor), k5(5th distortion factor).

If I resize the chessboard images by half so that the width and height of the resized images are w/2 and h/2 respectively and conduct camera calibration again, I would expect to theoretically get fx/2 ,fy/2, cx/2 and cy/2 as focal length x, focal length y, principal point x and principal point y respectively.

How about distortion factors ? What would I expect to get theoretically the 1st, 2nd, 3rd, 4th and 5th distortion factors of the resized chessboard images in terms of k1, k2, k3, k4 and k5 ?

- They dont change. They are function of X/Z and Y/Z. Check http://www.vision.caltech.edu/bouguetj/calib_doc/htmls/parameters.html. Only the intrinsic matrix changes, not the distortion coefficients.Mar 16, 2016
- If after seeing the link you have doubts, grab a rectified image, apply a very strong distortion (choose some coefficients), then resize. Compare with the rectified image resized first and then distorted with the same coefficients. If you fix the intrinsic matrix correctly, they should match with the same distortion params.Mar 16, 2016
- +José Jerónimo Moreira Rodrigues I got it. I got it !!. Thanks a lot. I have been calibrating cameras for many years but I have not have any idea about camera model and distortion model (How embarrassing!). Now I realized that all stuffs about distortion are just a story before scaling by focal length.Mar 16, 2016