Research On Quality Improvement Technology Of Computer-generated Holographic Image

The research on 3D display technology continues to develop,and people hope to obtain a more realistic visual experience.Existing three-dimensional display technologies,such as parallax display and volumetric display,are unable to provide true depth information of three-dimensional objects.As a true three-dimensional display technology,holographic display can provide all the depth information required by the human eye to perceive three-dimensional objects,giving people a comfortable and realistic three-dimensional stereo visual sense.Holographic display technology has a wide range of applications in military,medical and other fields,such as the display of aircraft cockpits,medical imaging.The development of computational holographic display technology still suffers from poor image quality,slow computational speed,small size of the holographic image and narrow field of view(FOV).Among them,speckle noise is an inherent problem of computational holographic display and restricts its further development.Many scholars have proposed various methods to suppress the speckle noise,but they have not yet achieved the desired effect.In addition,due to the limitations of the current process,the FOV of the holographic reproduction image of a single spatial light modulator(SLM)is narrow,which further reduces the comfort of viewing.In recent years,researchers at home and abroad have done a lot of research to solve this problem and have proposed various methods to expand the FOV,but there are also certain limitations.In this paper,the image quality is improved from two perspectives of suppressing speckle noise and expanding FOV.The research work in this paper is as follows:Firstly,the background and significance of the research are introduced.We briefly describe the current status of holography,speckle noise suppression of reconstructed image and FOV of image enlargement.In addition,the basic principles of computational holographic display are analyzed,mainly introducing scalar diffraction theory and optical Fourier transform.Afterwards,the generation and reconstruction of holograms are introduced from both optical holography and computational holography,SLM,the key electronic device used in computational holography,is also introduced,and its basic structure,pixel structure and phase modulation principle are described in detail.The FOV characteristics of computational holographic reproduction image based on SLM are analyzed.Secondly,the method of suppressing speckle noise in computational holographic displays is investigated.Moreover,the principle of speckle noise generation is analyzed;the basic theory of laser speckle and the mechanism of speckle noise generation in computational holographic displays are introduced.Then,several methods of suppressing speckle noise are analyzed,including the GS algorithm,the pixel separation method and the time averaging method.Afterwards the speckle contrast for image quality evaluation is briefly described.In addition,the pixel separation method is used for simulation experiment,the main experimental results are given,the advantages and disadvantages of the method are analyzed.On this basis,the follow-up research work of this paper is carried out.Finally,we propose a large FOV holographic display method in which the speckle noise is suppressed.Unlike conventional methods,this method generates multiple sub-computed-generated holograms(sub-Computer-generated hologram,sub-CGH)of large size.The recorded objects are separated into object point groups by pixel separation.The information of each object group is recorded on different sub-CGHs,with independent initial random phases.In the holographic reconstruction,three SLMs with a linear arrangement structure are used to load the sub-CGHs,and the image is reconstructed by time multiplexing.The FOV is enlarged because the size of the light distribution at each image point is increased.At the same time,the speckle noise of the image is suppressed by averaging effects and separation of adjacent image points.The experimental results demonstrate the feasibility of the method.