I am trying to use K1 and K2 to correct radial distortion in camera calibration using functions from OpenCV. There are four kinds of combination of sign of K1 and K2:
A K1: positive K2: positive
B K1: positive K2: negative
C K1: negative K2: positive
D K1: negative K2: negative I encounter A， B and C. Is there special meanings for the sign of K1 and K2? There are two kinds of radial distortion: barrel distortion and pincushion distortion. Is the sign of K1 and K2 related to the kind of radial distortion? The more the absolute value of K1 and K2, the larger radial distortion?
Yes, from the docs at Camera Calibration and 3D Reconstruction
"barrel distortion (typically k_1 > 0 and pincushion distortion (typically k_1 < 0)."
And yes, the greater the value the greater the distortion.