Research On Light-Fieldrefocusing Algorithm In Frequency Domain

The traditional imaging system records the projection on two-dimensional image plane of the light field of the scene in a way of what you see is what you get, missing the directional information of light and restricting the development of optical imaging. With the increasing investment on light field imaging theory and continuous progress of industrial technology, light field imaging system employs novel optical instruments to record full information of light field in the scene and overturns the traditional imaging pattern by its powerful post-processing ability, so light field imaging has a great research significance. Currently, the research related to light field is still at a preliminary stage and the studies on light field imaging theories and applications are far from adequate. This thesis analyzed the principles of light field imaging and the processing of light field data in detail, and further studied the light field refocus algorithm in frequency domain. The main contents and fruits of this thesis are listed as follows:Firstly, this thesis reviewed and analyzed the basic theory of light field imaging and refocusing. Through the ray-space diagram, we discussed the difference between traditional imaging and light field imaging, and analyzed the mechanism of light field imaging. On this basis, we reviewed the refocusing theory of light field imaging in spatial and frequency domains. The equations of refocusing in frequency were derived based on the Four-dimension Fourier Slice Theorem.Secondly, in order to ensure the implementation of light field refocusing, we completed the whole process of calibration, rectification and extraction from the two-dimension light field image to four-dimension light field data, and thus prepared the light field data for the subsequent refocusing. Considering the indeterminacy of micro-lens array, process and assembly error of devices, and distortion of optical elements, we presented a series of solutions to deal with the calibration of micro-lens array, color correction, grid rectification of micro-lens array, intrinsic parameters of light field camera, distortion rectification and extraction of sub-aperture images.Thirdly, with the purpose of acquiring a more universal refocusing equation in frequency domain, we generalized the two-dimension Fourier Transform Similarity Theory and the Affine Theorem into N-dimension situation, proposed and proved the N-dimension Fourier Transform Similarity Theory on account of the presently two kinds of light field imaging technology, traditional light field imaging and convergent light field imaging. We proposed a N-dimension Fourier Transform Slice Theory based on N-dimension Fourier Transform Similarity Theory and gave out a method on derivation and demonstration of this theory. Besides, we proposed a derivation method for Fourier Slice Theory on four-dimension light-field imaging, which simplifies the existing methods.Fourthly, based on the proposed N-dimension Fourier Transform Slice Theorem, and considering the limitations of the size of image sensor and the characteristics of discrete sampling, we expressed the light field signal as periodic continuous signal, then performed discrete sampling on it, and further proposed a novel refocusing algorithm based on fractional Fourier transform to realize the refocusing of light field data.