How to correctly calibrate my camera with a wide angle lens using openCV?

Question

I am trying to calibrate a camera with a fisheye lens. I therefor used the fisheye lens module, but keep getting strange results no matter what distortion parameters I fix.

Answer 1

Your first problem is that you are only using one image. Even if you had an ideal pinhole camera with no distortion, you would not be able to estimate the intrinsics from a single image of co-planar points. One image of co-planar points simply does not give you enough constraints to solve for the intrinsics.

You need at least two images at different 3D orientations, or a 3D calibration rig, where the points are not co-planar. Of course, in practice you need at least 20 images for accurate calibration.

Your second problem is that you are using a carpet as the checkerboard. You need to be able to detect the points in the image with sub-pixel accuracy. Small localization errors result in large errors in the estimated camera parameters. I seriously doubt that you can detect the corners of the squares of your carpet with any reasonable accuracy. In fact, you cannot even measure the actual point locations on the carpet very accurately, because it is fuzzy.

Best of luck!