Wide-angle lenses distortion calibration using phase demodulation of phase-shifting fringe-patterns

A distortion calibration method for wide-angle lens was proposed based on fringe-pattern phase analysis. Firstly, four standard cosine fringe-patterns with phase shift step of π/2, which were used as calibration templates, were shown on a large-size Liquid Crystal Display screen, and captured by the camera with wide-angle lens to obtain four distorted fringe-patterns. A four-step phase-shifting method was employed to obtain the phase distribution of the radial distorted fringe-pattern. There was no distortion within the central region of the image captured by the wide-angle lens, so the phase distribution of radial undistorted fringe-pattern, as a benchmark for computing radial distorted phase, could be acquired by performing numerical fitting by the central undistorted phase value of the distorted image. It means that the radial distorted phase distribution was computed by subtracting the phase distribution of radial distorted fringe-pattern from the phase distribution of radial undistorted fringe-pattern. Finally, the distorted phase was transformed into the actual distorted variables. There was no need to establish any kind of image distortion model by lots of characteristic points or lines. Furthermore, the radial distortion variable at each point of the distorted image can be determined by the proposed method. Experimental results show that the proposed method is simple, effective, and has wide application value.