camera calibration MATLAB toolbox

Question

I have to perform re-projection of my 3D points (I already have data from Bundler).

I am using Camera Calibration toolbox in MATLAB to get the intrinsic camera paramete

Answer 1

The camera calibration toolbox extract grid points from the checker board images and uses it for finding calibration parameters.

The pixel errors are mean re-projection error for extracted grid points, i.e. the actual pixel location and the one by using calculated K matrix. So these numbers are mostly within 1 (1 pixel error) although your numbers are quite. The error in focal length is variance of calculated focal length.

You need only 3 or 4 images to find calibration of a camera (I forget the actual number). If you provide multiple images, it will compute K for all the combination of 3-4 images and compute a K. The errors are the variance of all these computed K.

Your numbers are quite high (it should be within 3-4 pixels compared to your 22-23 pixels). The reason is bad images for calibration and wrong initial estimate of grid points (this you do manually by selecting 4 corners in image). Also usually f_x and f_y are same in modern cameras and you should take mean of both (f_x + f_y)/2.

Regarding your principle point, it seems your camera resolution in 1920 x 1600 and you should use [980 800] instead of the one given by toolbox. Usually the ccd is placed carefully now-days and you have your principle point exactly at the center.