Optical distortion evaluation based on the Integrated Colour CCD Moiré Method.

Camera calibration is an important part of high-precision optical measurement, which is especially difficult in the micro-nano field. Based on the integrated correlation calculation and CCD moiré method, this paper describes the development of a lens calibration technique called the Integrated Colour CCD Moiré Method (ICCM). The CCD moiré fringes, formed by superimposing a periodic optical signal of a specimen grating with a CCD target array or a Bayer filter array, significantly enlarges the deformation modulated by lens distortion and the calibration plate attitude (i.e. the rotation angle relative to the camera coordinate system). To measure lens distortion using CCD moiré, the deformation pattern that is governed by the lens distortion, specimen grating attitude and carrier was used to construct a CCD fringe image. If the constructed CCD fringe image based on the trial lens distortion and rotation angles have a maximum similarity to the captured CCD moiré image, the lens distortion and rotation angles are correctly inversed. Particle swarm optimisation algorithm was selected to search for the true value so that the accuracy and robustness could be improved. Numerical experiments verified that the ICCM method developed in this work can simultaneously inverse the lens distortion, rotation angle and the grating pitch with high precision. The lens distortion of the metallographic microscope has been successfully characterised by the developed method with an 833 nm pitch grating. Simulations and experiments showed that ICCM is an intuitive, accurate, anti-noise and robust distortion calibration method.