Image Quality Optimization Of Lensless Fourier Transform Digital Holography

Compared with traditional optical holography,digital holography has many advantages,such as fast imaging,convenient operation,etc.It is worth mentioning that,the reconstructed image of digital holography can be optimized in real time based on digital image processing techniques.Because of these unique advantages,digital holography has been widely used in many fields such as Measurement,storage,and particle tracking.In allusion of the key problem that the current speckle noise and zero-order image seriously reduce the image quality of digital holographic reconstruction,this paper proposes a method based on Laplace transform and pixel value distribution statistical to remove zero-order image,a selective spatial domain mask method to reduce speckle noise,and a method based on hologram region segmentation and recombination to reduce speckle noise.The main work of this paper is as follows:In Chapter one we introduce the four main stages of holographic development as well as the advantages and disadvantages of digital holography.We also illustrate the multi-domain and multi-layer applications of digital holography,and the research status of digital holographic noise reduction and zero-order image removal at home and abroad.In Chapter two we analyze the wavefront recording and wavefront reproduction in digital holography,as well as the conditions of digital holography recording.It is expounds that the lensless Fourier transform digital holography not only improve the utilization of the effective bandwidth of CCD during the recording process,but also can reproduce all the information of the object in one reproduction process.Greatly reduces the loss of object phase and amplitude information.In Chapter three we illustrate a method that Laplace transform is applied to the hologram of digital holography and the zero-order image can be effectively removed after being reconstructed.Based on the fact we mention above,an optimization method is proposed in the paper.According to the pixel value histo gram of the image,a reasonable threshold is set,which not only removes the zero-order image further,but also reduces the influence of speckle.In the paper,the optical path is built by optical platform,and the lensless Fourier transform digital hologram is recorded.The original method and the new method both are used to reconstruct the hologram.Through subjective and objective analysis,it is verified that the new method can not only further remove the residual of the zero-order image,but also enhance the contrast of the reconstruction images and reduce the speckle noise.In Chapter four we introduce the causes and distribution characteristics of laser speckle in the reconstruction of digital holography,and then we focus on the principle of reducing the speckle noise by the traditional spatial mask method.In view of this,we propose a selective spatial domain mask method and a method based on hologram regional segmentation and recombination in the paper.Based on the experiment of lensless Fourier transform digital holography,we compare two new methods with the traditional spatial mask method.Subjectively,the reconstructed images obtained by the two new methods can effectively reduce the redundancy.Objectively,the two new methods are more advantageous than the traditional spatial domain mask method in terms of processing time,EPI value and ENL value.It has been experimentally proved that the selective spatial domain mask method and the method based on hologram regional segmentation and recombination can reduce the speckle noise of the reconstructed image more quickly,and better enhance the quality of the reconstructed image.