Calibration Experiments Of Subaperture Measurement System And Research Of Wavelet Edge Detection Based On Wavelet Algorithm

Wavelength and aperture size will limit the angular resolution of traditional optical imaging system. Synthetic aperture interference imaging technology, which resolved the technological problem of optical imaging system with single large aperture, provided a new way for improving the imaging system resolution. As it is an array of smaller off-axis sub-apertures arranged and spliced into an imaging system with large aperture, so the wave-front measurement and control system is necessary to realize a high stitching precision between the sub-apertures. Compared with the whole piece optical mirror, the boundaries of the segments in synthesis sub-aperture imaging system are more complex, which have more information and more edge areas. For these reasons, it is necessary to research the co-phasing test of sub-aperture imaging system.Through analysis of alignment system and researches of camera calibration, nonlinear distortion correction, and edge detection algorithm, our studies try to lay a preliminary foundation for the further work of sub-aperture surface measuring and co-phasing testing. Since the structure light method has the advantages of high precision and is easily to achieve, we use it as the model of our work to calibrate CCD camera, correct distortion, align the test system, and extract the edge based on theory of wavelet transform. Firstly, we completed the camera calibration with Zhang Zhengyou calibration system, and obtain the internal/external parameters of camera and lens by MATLAB calibration toolbox. We analyze the principle of lens distortion and the correction algorithms, eliminate image distortion combined with the parameters obtained from the previous steps, and design a spots array test for verification. In addition, we adopt a series of interpolation methods, such as recently took interpolation, bilinear interpolation and bucolic interpolation method to fill the void holes and obtain the distortion-free image. Subsequently, the high precision alignment of the system and the improvement of the method were carried out. The design of the cross wire method can synchronized to achieve the calibration of the rotation error and the center error, the precision could reach 1 pixel. In the further improved calibration scheme, the use of interferometry and center spot alignment method respectively installed adjustable, precision could reach 0.1 pixel. Finally we extracted image edge by using the cubic b-spline as the smoothing function based on multi-scale wavelet algorithm. After the multi-scale wavelet decomposition of the whole image, we figure out the local modulus maxima in gradient directions. However, it also contains noise, and thus adaptive threshold method is used to select the modulus maxima, Finally, we use corrosion and expansion deal with the resulting image to get the consecutive boundary of image. In the MATLAB environment, the proposed algorithm is tested and simulated, and the experimental results show that the proposed method has better edge extraction capability.