Research On The Effect Of The Sparsity Of Speckle On The Quality Of Computational Imaging

Ghost imaging,also known as correlation imaging,is a non-local imaging method,which uses the second-order correlation function to calculate the obtained light intensity information,so as to reconstruct the information of the object to be measured.Non-local imaging has the advantages of strong anti-interference ability,can penetrate scattered medium imaging,and has broad application prospects.However,the actual imaging process also faces problems such as more complex imaging systems,the general need for a laser as the light source,the need for more sophisticated spatial light modulators.In addition,the imaging results also have limitations such as poor contrast,low contrast to noise ratio,slow imaging speed,and a large amount of measurement data are required,which seriously restricts the practical application of ghost imaging.In this paper,the high refresh frequency liquid crystal display is used to realize the lensless computational ghost imaging successfully,which greatly simplifies the imaging system and reduces the cost,and can provide a new way for the practical application of ghost imaging technology.On this basis,the effect of sparsity of white speckle on the imaging quality in the system with high background noise is investigated.The main research contents are as follows:1.The lensless computational ghost imaging was successfully implemented using a high refresh frequency liquid crystal display based on Free Sync technology as the light source.The effects of the number of speckle patterns,the size of speckle patterns,the brightness of liquid crystal display screen,contrast,refresh frequency,the gain coefficient of photodetector and the distance between photodetector and liquid crystal display screen on the quality of ghost imaging were studied.The results show that the imaging quality is obviously improved with the increase of speckle pattern quantity.If the speckle size is too small,the image quality is very low,while if the speckle size is too large,the image mosaic phenomenon is serious.Monitor screen brightness increases,image quality gradually improves.Changing the contrast ratio of the monitor screen and the screen refresh frequency,the difference in quality of the image obtained by reconstruction is not large,but a higher refresh frequency can improve the imaging speed.When the gain coefficient of photodetector is 40 db,50db,60 db,the image is more clear.The image is clearest when the distance between the photodetector and the liquid crystal display screen is 50mm-70 mm.This can provide guidance for the design of ghost imaging system based on high refresh liquid crystal display with Free Sync technology.Due to the wide coverage and low price of liquid crystal display,ghost imaging based on liquid crystal display will reduce the cost of imaging system,greatly promote the practical application of ghost imaging.2.On the basis of research content 1,the effect of sparsity of white speckle on imaging quality and correlation calculation time in a system with large background noise is studied by reducing or increasing the number of white speckle.The experimental results show that appropriate increase of the sparsity of white speckle can increase the absolute amplitude and relative amplitude of light intensity fluctuation,improve the image quality of ghost imaging,and increase the contrast-tonoise ratio of reconstructed image by 20.59%.In addition,increasing the sparsity of white speckle can increase the sparsity of matrix in the correlation calculation,thus reducing the correlation calculation time.The method does not require complex processing of the speckle,is simple to operate,and has important application prospects in the practical application of computational ghost imaging.