How to turn your camera into a perfect pinhole model
Ivan De Boi Stuti Pathak Marina Oliveira Rudi Penne
Camera calibration is a first and fundamental step in various computer vision
applications. Despite being an active field of research, Zhang's method remains
widely used for camera calibration due to its implementation in popular
toolboxes. However, this method initially assumes a pinhole model with
oversimplified distortion models. In this work, we propose a novel approach
that involves a pre-processing step to remove distortions from images by means
of Gaussian processes. Our method does not need to assume any distortion model
and can be applied to severely warped images, even in the case of multiple
distortion sources, e.g., a fisheye image of a curved mirror reflection. The
Gaussian processes capture all distortions and camera imperfections, resulting
in virtual images as though taken by an ideal pinhole camera with square
pixels. Furthermore, this ideal GP-camera only needs one image of a square grid
calibration pattern. This model allows for a serious upgrade of many algorithms
and applications that are designed in a pure projective geometry setting but
with a performance that is very sensitive to nonlinear lens distortions. We
demonstrate the effectiveness of our method by simplifying Zhang's calibration
method, reducing the number of parameters and getting rid of the distortion
parameters and iterative optimization. We validate by means of synthetic data
and real world images. The contributions of this work include the construction
of a virtual ideal pinhole camera using Gaussian processes, a simplified
calibration method and lens distortion removal.