Improvement Of Imaging Quality Of Fourier Ptychographic Microscopy

With the development of society,people’s requirements for microscopy imaging system are increasing,which promotes the continuous development of microscopy imaging technology.For example,in pathology,hematology,immunohistochemistry and neuroanatomy,not only large imaging field of view is required to meet the needs of observation and detection range,but also high-resolution is required to meet the needs of meticulous and precise detection of samples.Therefore,in the fields of biological research,surface morphology detection,disease prevention and detection,it is more and more urgent to develop a new micro imaging method which not only can not sacrifice the traditional microscopy imaging technology,but also can have a higher resolution.Because the imaging ability of optical system is fundamentally limited by the spatial bandwidth product of optical system,even for the extremely large numerical aperture or amplification coefficient,the spatial bandwidth product of conventional microscopic imaging system is usually only one million pixels.In the process of increasing the spatial bandwidth product of the microscopy imaging system,there is a balance between the achievable image resolution and the field of view due to the geometric aberration caused by the physical size of the optical elements.The application of biology,medicine and other fields should have a large space bandwidth product for imaging system,which promotes the commercial development of complex mechanical scanning microscope system and lensless microscope device.However,these imaging system implementation methods are not only relatively complicated,but also need to accurately control the driving,optical alignment and motion tracking,so it is not conducive to the promotion and use.The method of Fourier Ptychographic Microscopy(FPM)does not need to move the sample,and uses the Light Emitting Diode(LED)array as the light source to provide multi angle illumination,so it can recover the high-resolution complex amplitude of the sample large field of view without complex mechanical scanning experimental device.However,the aberrations caused by large angle illumination and the noises in the system will affect the quality of the reconstructed image.In this paper,the theoretical and experimental research on the frequency overlapping rate of FPM and the image restoration applied to the degraded image is carried out.The main contents are as follows:The simulation research on the overlapping rate of spectrum,the number of iterations is carried out.The definition of spectrum overlapping rate is given,the calculation method and influencing factors are deduced.The influence of different spectrum overlapping rate and iteration times on the reconstruction quality of FPM is analyzed by simulation,and the influence of spectrum overlapping rate and iteration times on the reconstruction quality is quantitatively analyzed by a variety of evaluation functions.It is concluded that the best frequency overlapping rate is about 60%,and the best iteration times are about 20.Through simulation,the degraded image with distortion and noise is obtained,and the image restoration based on Wiener filter algorithm is carried out to improve the image quality of FPM.Then,based on BX51 Olympus microscopy,an experimental system of FPM is built.The low-resolution intensity images of USAF 1951 test target sample recorded by CMOS camera were synthesized in frequency domain by FPM method to obtain the high-resolution complex amplitude of the sample.The experimental results show that the resolution of the system is improved from 3.48 ?m to 1.74 ?m by using the FPM method when the magnification of the microscope objective is 4 × and the numerical aperture is 0.1,keeping the field of view unchanged,and the high-resolution amplitude and phase images of the sample are obtained in the same time.Based on L-R image restoration algorithm,the image quality of the FPM is improved applied to the reconstruction results in experiments.