Research On Ghost Imaging For Grayscale Object Based On Binary Detection

Correlation imaging,also called ghost imaging,has attracted much attention of researchers because of its characteristic of non-local imaging.Different from the imaging mode in traditional imaging method of directly imaging by obtaining the object information from a photo-detector,correlation imaging mainly reconstructs the target image by the second-order correlation measurement of the light intensity,it doesn't require the two-dimensional detection of the object.In the long-distance optical communication,channel interference and the loss of light intensity during the transmission may weaken the light intensity which reaching the detector,even to the level of single photon.At this time,it is difficult to obtain an image by the directly imaging method,and the correlation imaging can reconstruct the image by calculating the data of the signal path and the reference path.This paper discusses the reconstruction of grayscale target in ghost imaging with different quantitative situations,and focuses on the imaging ability of correlation imaging method based on binary detection for the grayscale object.The main contents of this paper are as follows:Firstly,we discuss the quality of the reconstructed grayscale images in correlation imaging after quantifying the data of different optical path.According to the quantification principle,it is divided into three cases: quantize the data of signal arm only,quantize the data of reference arm only,quantize both of the signal arm and the reference arm,the number of quantization bit is 1 to 4 bits,then the quantized information are correlated to reconstruct the image.In this paper,two parameters,the peak signal-to-noise ratio and the correlation coefficient are used to evaluate the image quality.The results show that when the data of reference arm is quantized into lowlevel,the quality of the reconstructed image is obviously reduced,and the change on the data level of reference arm brings great impact to the imaging quality of ghost image.When quantifying on the data of signal arm only,even to one bit(binary)quantization,the influence on the image quality is the smallest in the three cases above.Secondly,we analyze the image quality of quantifying the data of signal arm from one to four bits,and compare the quantitative results of different bits with the normal ghost image.It is found that the image of a four-slit grayscale object can still be reconstructed by the correlation imaging method when the data of the signal arm even reaches to binary level,and the reconstructed result is close to high-bit quantization ghost imaging and normal ghost imaging.Finally,we focus on the imaging ability of ghost imaging with binary detection for different grayscale targets.With the increase of correlating numbers,the normalized intensities of the four slits which have different grayscale values are calculated,and the results are compared with normal ghost imaging.It is shown that the reconstruction of the target with higher grayscale value performs better in binary ghost imaging,and the difference of the normalized intensity between the reconstructed result of the lowest grayscale target and the original object is about 30% higher than that of the normal ghost imaging.In order to further investigate the reason why the reconstructed result for low-grayscale target is not ideal in ghost imaging with binary detection,we analyze the signal-to-noise ratio of different reconstructed slits.The results show that,with the increase of correlating numbers,the SNR of the target object with lower grayscale value is lower,and the existence of noise affects the reconstruction result of lowgrayscale object.Finally,by changing the threshold of binary detection,we find that there is an optimal threshold exists to achieve the optimum image quality in ghost imaging with binary detection.