Research On Removal Method Of Speckle Noise In Hologram Reproduction Image

With the development of the times,holography has gradually become an important research direction of information optics.The hologram and reconstructed image preparation process in holography can be divided into two processes: the recording process and the reproducing process.According to the different equipment used in these two processes,holography can be divided into optical holography,computing holography and digital holography.Optical holography is the earliest invention of holography,which uses the silver salt dry plate to record the object light and reference light interference fringes to obtain hologram,and then through the hologram optical diffraction to get a reconstructed image.Computing holography use computer and plotter to record the amplitude and phase in the transparent film according to the mathematical description of the object wave,and obtain the computer synthesized hologram.Holography can be recorded on the virtual object,and optical holographic objects can only exist when the actual production.Digital holography using CCD element to replace silver salt dry plate,the results are entered into the computer to obtain reconstructed image.The recording optical path of digital holography and optical holography is the same,and both of them need the actual object.Combined with computer technology and the latest imaging technology,digital holography can avoid the cumbersome optical holography of the physical and chemical processing,while have advantages of low cost and high imaging efficiency.Speckle noise is a major problem that hinders the image quality of a reconstructed image of a hologram.Due to the presence of speckle noise,the clarity of the reconstructed image is reduced and the edge of the image is blurred,which seriously affects the application of holography in various fields.The physical mechanism of speckle noise is that the highly correlated laser is reflected on the surface of the object and coherently superimposed to form the granular speckle noise on the hologram.At present,the method of removing speckle noise is mainly composed of optical method and digital image method.The main purpose of this paper is to study how to use digital image method to remove speckle noise.The objectives and achievements of this paper are as follows:1.Firstly,this paper theoretically introduce three kinds of holography.Combined with digital holography and holographic characteristics,this paper use of Bo Qi code to achieve the hologram recording and reproducing.The mechanism of speckle noise is studied,the holographic noise and the noisy reconstructed image are obtained by using the matlab method to add the speckle noise to the hologram.2.The commonly used digital image method is researched and compared,and Lee filter is selected as the typical research object.Lee filter is a local statistical spatial filter,which has a good suppression effect on multiplicative speckle noise.On this basis,the researchers proposed enhanced Lee filter,the algorithm according to the standard deviation coefficient of the range of different filters to filter.When the standard deviation coefficient is in the flat region and the non-development region,the mean value filter and the original value are used respectively.In this paper,the improved Lee filtering is improved,and a weighted weighted Lee filtering algorithm is proposed.Compared with the contrast algorithm,this algorithm has better peak signal to noise ratio and image quality.3.In this paper,a two-step denoising method is proposed in this paper.Firstly,the pulse-coupled neural network(PCNN)is used to denoise the noisy hologram,and then the reconstructed image is reconstructed and the reconstructed image is filtered by Lee filter processing.The experimental results show that the proposed algorithm has higher peak-to-noise ratio,better speckle index and better visual quality,compared with denoising using Lee filter alone.This shows that this method can effectively improve the quality of digital hologram.