| In the process of imaging recording,digital holography can use different light path structures to get different types of holograms,namely coaxial or off-axis digital hologram.The coaxial digital holography not only has simple optical path structure,but also makes full use of the space bandwidth of the camera.The off-axis digital holography is complicated in optical path structure,whose conjugate image,the zero-order image and the original image are separated in the frequency domain.Phase extraction and measurement can be carried out by single image.Both the coaxial and the off-axis digital holography have their own advantages.They are widely used in precision instrument detection,biological micro measurement,three-dimensional shape and deformation monitoring,temperature field measurement and other research fields.In the original image reproduction stage of digital holography,the existence of zero-order image and conjugate image results in poor reproduction quality of the original image.Therefore,it is of great academic and practical significance that how to better suppress the interference between the zero-order image and the conjugate image to the reproduced image and to improve the quality of the reproduction image as much as possible.This subject,Phase extraction technology of digital holography based on iterative least square,uses the least square iterative fitting method to deal with the coaxial and off-axis digital holograms.Through the design of the algorithm,the zero-order image and conjugate image are effectively suppressed,and the phase reproduction is achieved in higher quality.The main contents of this paper are as follows:First,the basic theory of holography is systematically expounded.Starting from the optical knowledge involved in holographic imaging,the basic theory of Fresnel diffraction is briefly introduced.The basis of classification and the principle of reconstruction and recording in digital holography are emphatically analyzed.The traditional coaxial and off-axis phase extraction techniques are introduced respectively,whose shortcomings are analyzed.Second,for the coaxial and off-axis digital holograms,the phase extraction techniques based iterative least square are researched.The phase extraction technology of coaxial digital holography based on iterative least square achieves the phase-shift randomization in recording holograms and the automation of algorithms in reconstructing phase.Compared with the traditional phase extraction algorithm for coaxial digital holography,such as three step or four step phase shift method,it is more general and has a wider application range.The phase extraction technology of off-axis digital holography based on iterative least square is performed entirely in the spatial domain,then another background hologram is used to remove the carrier component.Compared to the traditional off-axial digital holography phase algorithm,such as frequency domain transform methods,it avoids operations such as filtering and localization in the frequency domain.The phase reproduction can be completed better.Thirdly,for the slight off-axis and large off-axis digital holograms with the carrier,based on iterative least square,the phase extraction technology which can suppress carrier are researched.Aiming at the slight off-axis digital hologram generated by the coaxial digital hologram?s equipment,which introduces carrier due to environmental interference or unstable device in imaging process,the phase and carrier extraction technology of slight off-axis digital holography based on iterative least square is studied,which effectively extracts and suppresses carrier and achieves the phase reproduction better.For the large off-axis digital holograms,combined with the spatial shift and phase shift expansion,the phase and carrier extraction technology of off-axis digital holography based on iterative least square is proposed.Compared to other off-axis phase extraction techniques,this technique only utilizes single image,and the carrier can be accurately determined(accuracy is 10-5 rad/pixel).The carrier is suppressed in the phase extraction process without the background image.The phase reproduction can be completed expediently and accurately.Finally,MATLAB is used to verify the feasibility,applicability and phase extraction quality of the algorithm,and separatly tested the simulated sphere,general picture and real hologram.The phase extraction algorithm is completed iteratively in spatial domain and has a long run time.Therefore,we accelerate the proposed algorithm based on OpenCV and GPU,and the acceleration effect is remarkable.In order to meet the needs of practical engineering,based on VS and MFC,the application system based GPU,which can both extract off-axis digital holographic carrier and phase,is designed and completed,which is convenient for engineering applications and users. |
