The Research On The Key Techniques Of Automatic Reconstruction For Marine Organisms Holograms

Digital holography has gradually become one of the important tools for study and analysis of planktons and particles in sea and other waters.Electronic holographic camera based on digital holography has non-intrusive and non-destructive advantages on recording the samples' volumes for scientists' study.But captured holographic videos generally need relatively large capacity,and they cannot be processed in time.It becomes great obstruction for scientists to study on marine organisms and particles.In order to fastly process such immense data,to achieve automatic reconstruction of single hologram should be done firstly.Automatic reconstrion is that according to extremum search strategy,the best reconstruction distance is automatically determined by focus function on the computer to obtain the sharpness reconstructed image.In addition,holographic video often has more severe inclined stripe noise caused by optical elements due to holographic camera.The stripe noise has serious impact on reconstructed image quality,and effects estimation of sharpness function for the reconstructed image,and also affects automatic reconstruction of the hologram further.Therefore,it is very important to develop a novel,fast and automatically reconstructing method for massive holographic videos.To reach the aim,the thesis has studied and analyzed the influence factors on the fast automatic reconstruction thoroughly,such as suppression method for inclined stripe noise in the holograms of marine organisms,the focusing criterion function and the extremum search strategies.Corresponding solutions have then been put forward and tested on the representative actual holograms of the marine organisms.The results show that,the proposed methods have mainly achieved the aim of fast automatic reconstruction for those holograms.The detailed novelties are stated as following:Firstly,as the inclined stripe noise has influenced the smoothness of focusing criterion,after the existing stripe noise suppression methods have been studied,the frequency characteristics of the inclined stripe noise have then been analyzed.A hybrid inclined stripe noise suppression method has been proposed.In this method,to describe the inclined stripe noise in frequency domain accurately,an approaching based on fitting function has been proposed.To suppress periodic inclined stripe noise and avoid the loss of useful information simultaneously,Gaussian notch filter for periodic inclined stripe noise and local notch filter for aperiodic inclined stripe noise have been applied.it has been tested on some actual shooting holograms of the marine organisms.The results show that,the proposed method can suppress the inclined stripe noise in the holograms of marine organisms effectively.Secondly,aiming at the factor of focusing criterion influencing the fast automatic reconstruction,the existing focusing criterions have been studied.On the basis of those criterions,four novel focusing criterion functions based on local variance or local standard deviation distribution has been proposed.To improve the robustness of focusing criterion,the local variance distribution instead of gradient has been applied to extract edges of reconstructed image.We have tested the new approaching on some actual holograms of the marine organisms,and compared it with others.The results show that our proposed one is robust with better performance in all the tested holograms.Thirdly,aiming at the extremum search strategies influencing the fast automatic reconstruction,on the basis of study on the existing extremum search strategies,a five-points model method is proposed,after we have discussed two of them: model method and five-point method.In the proposed method,to improve the questions of redundant search and sensitivity to start,focus form model is established and slope criterion is proposed;to improve the robustness of the search strategies,some anti-interference measures are added;to guaranteeing precision of the search strategies,the depth of focus of hologram is as the end condition for searching.And the computation of focus depth for in-line digital hologram has been proposed according to that for off-axis hologram.the proposed method has been tested on some actual holograms of the marine organisms,and compared it with others.The results show that the proposed method has stronger search capacity and robustness,and effectively resolved extremum search problem in the fast automatic reconstruction.