| The fabrication of micro structure components is one of the key research areas in advanced manufacturing technology.And in the processing of micro structure surface,the measurement of its three-dimensional(3D)profile is the key step to guarantee the manufacturing accuracy.The existing measurement methods for micro structure surface are all based on the scanning scheme.These scanning-based methods are difficult to meet the requirement of on-machine measurement,which needs a real-time feedback of the parameters during the processing.Light field microscopy(LFM)is a 3D imaging method that has been applied to micro structure surface.LFM can obtain the 3D information of the surface through a single exposure and can be realized in on-machine measurement with a good application prospect.However,due to the influence of the sparse texture and the high reflectivity of the micro structure surface,the depth information extraction of the existing 3D measurement method based on LFM is not robust and accurate enough.And compared with conventional microscopy,microlens array based LFM has a serious problem of horizontal resolution loss.According to the demand of microstructure surface measurement and the characteristics of light field microscopy,this thesis has done the following research work.1.Light field microscopic imaging model is analyzed based on geometrical optics and light field visualization,which laid the foundation for further research.A mathematical model of light field microscopic imaging is established through the functional characterization of the four-dimensional(4D)light field.The digital refocusing and view separation of light field data is realized by coordinate transformation of the light field data.2.3D reconstruction based on light field data is studied,which uses a combination of defocus and correspondence clues of light field data.According to the characteristics of digital refocus images,the depth estimation method based on defocus cues is achieved.Depending on the characteristics of view separation images,the depth estimation method based on correspondence cues is achieved.Based on the situation that inaccurate extraction is likely to exist in the depth estimation of one single cue extraction,the method of image information fusion is applied to the 3D reconstruction of the micro structure surface.3.Resolution enhancement based on frequency domain analysis is performed.The influence of the light field optical system on frequency sampling is discussed from the perspective of frequency domain.An optical field imaging model based on wave optics is discussed to deal with diffraction effect.The 3D deconvolution algorithm is applied to realize the resolution enhancement of light field microscopy.In order to solve the limit of space-bandwidth product,Fourier ptychography microscopy is applied to the light field microscopy system to enhance the resolution.4.The experimental system is designed and built up,and micro structure surface measurement experiment is carried out.According to the requirements of the measurement method,the system parameters of the main components are analyzed and calculated,and the experimental system is designed and constructed.A measurement experiment of the micro structure surface was conducted.And the experimental results verified the effectiveness of the 3D reconstruction and resolution enhancement methods designed in this thesis.The error sources of the experimental system are analyzed and some improvement methods to reduce the measurement error are proposed.This thesis focuses on the research of 3D reconstruction and resolution enhancement in light field microscopy.We believe it lays a technical foundation for high precision quantitative measurement in the field of micro structure surface measurement by LFM. |
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