Computational Ghost Imaging System Research Articles

Computational ghost imaging system with 4-connected-region-optimized Hadamard pattern sequence

We propose a computational ghost imaging system based on the Hadamard patterns. A 4-connected-region-based method is proposed to optimize the Hadamard pattern sequence and a differential decomposition method is developed to construct a sequence that can be shown on the light modulation devices with the optimized pattern sequence. Finally, the image is reconstructed by the second-order correlation algorithm. Both numerical model and experimental setup are established and a series of experiments are implemented. The imaging performance of the proposed method is validated by comparing with the results from the default order of the Hadamard pattern sequence, Russian-dolls ordering and fast Walsh-Hadamard transform. The proposed system can realize high quality imaging with a low sampling ratio (5%–10%), and it requires much less measurement numbers for imaging.

Computational ghost imaging with discrete stochastic sources

Lots of digital devices were widely used in computational ghost imaging (CGI) to serve as optical sources and detectors. These digital devices greatly affect the statistical behaviors of the CGI system. In this paper, we attribute all the influence of these digital devices to the discrete probability density functions of the optical sources. We investigate CGI with three discrete optical sources, which emit intensities fulfilling Bernoulli, binomial, and Poisson distributions. We clarify the inner relation between the bucket signals and the reference signals by using their joint density probability functions. In correlation measurement, the visibility and signal-to-noise ratio of the ghost images greatly depend on the probability statistics of the sources. We find that CGI with discrete sources can surpass the classical visibility limit one-third in the thermal-light case. The simulation results confirm our theoretical predictions. Thus, the utility of the digital devices makes CGI manipulable and applicable in practice.

基于自适应对焦窗口的计算鬼成像目标深度估计方法

基于自适应对焦窗口的计算鬼成像目标深度估计方法

Depth estimation in computational ghost imaging system using auto-focusing method with adaptive focus window

Depth estimation in computational ghost imaging system using auto-focusing method with adaptive focus window

Adaptive compressed 3D ghost imaging based on the variation of surface normals.

Three-dimensional (3D) imaging can be reconstructed by a computational ghost imaging system with single pixel detectors based on a photometric stereo, but the requirement of large measurements and long imaging times are obstacles to its development. Also, the compressibility of the target's surface normals has not been fully studied, which causes the waste in sampling efficiency in single-pixel imaging. In this paper, we propose a method to adaptively measure the object's 3D information based on surface normals. In the proposed method, the regions of object's surface are illuminated by patterns of different spatial resolutions according to the variation of surface normals. The experimental results demonstrate that our proposed scheme can reduce measurements and preserve the quality of the formed 3D image.

Computational ghost imaging with uncertain imaging distance

Imaging distance plays an essential role in image formation in computational ghost imaging (CGI). Uncertain or unknown imaging distance often leads to the deterioration of the image quality or, even worse, to the failure of imaging. Here we present a CGI technique that provides high-quality image reconstruction in an uncertain distance environment. We propose a method to generate a stable speckle field, where the size of the field remains invariant and the field does not distort during light transmission, and find that the use this field removes the constraint imposed by the imaging distance. We experimentally and numerically verify the performance of the technique by applying it to a single-detector CGI system. The results show that the proposed technique provides excellent imaging performance, even when the imaging distance is uncertain, and can be extended to existing computational-based ghost-imaging schemes.

Improving the performance of computational ghost imaging by using a quadrant detector and digital micro-scanning

Computational ghost imaging systems reconstruct images using a single element detector, which measures the level of correlation between the scene and a set of projected patterns. The sequential nature of these measurements means that increasing the system frame-rate reduces the signal-to-noise ratio (SNR) of the captured images. Furthermore, a higher spatial resolution requires the projection of more patterns, and so both frame-rate and SNR suffer from the increase of the spatial resolution. In this work, we combat these limitations by developing a hybrid few-pixel imaging system that combines structured illumination with a quadrant photodiode detector. To further boost the SNR of our system, we employ digital micro-scanning of the projected patterns. Experimental results show that our proposed imaging system is capable of reconstructing images 4 times faster and with ~33% higher SNR than a conventional single-element computational ghost imaging system utilizing orthogonal Hadamard pattern projection. Our work demonstrates a computational imaging system in which there is a flexible trade-off between frame-rate, SNR and spatial resolution, and this trade-off can be optimized to match the requirements of different applications.

Computational ghost imaging and ghost diffraction in turbulent ocean

Computational ghost imaging (CGI) is an indirect single-pixel imaging method that can retrieve an image of an object in a hostile environment by using a correlation of intensity fluctuations. Based on the theory of ghost imaging (GI) and using the spatial power spectrum of the refractive index of ocean water, we develop a unified imaging formula for the CGI and computational ghost diffraction (CGD) operating through oceanic turbulence, and numerically analyse how the image quality can be affected by oceanic turbulence including the rate of dissipation of turbulent kinetic energy per unit mass of fluid, the rate of dissipation of mean-square temperature, and the relative strength of temperature salinity fluctuations, as well as the propagation distance. To quantitatively evaluate the quality of the retrieved images, the relative mean square error is employed in the CGI system. Our results show that the quality of the CGI scheme operating through oceanic turbulence is closely related to the propagation distance. When the propagation distance is fixed to be relatively small, we can effectively obtain a sharp image in the case of strong turbulence, and the turbulence influence can be neglected. Meanwhile the turbulence effects become more serious in the CGI system with increasing propagation distance. Besides, we find the CGI system is more robust against oceanic turbulence than the CGD system.

Auto-focusing method for computational ghost imaging system in deep-Fresnel region

The capacity of computational ghost imaging (CGI) in depth imaging is usually demonstrated by the technique of time-of-flight. However, this capacity could also be achieved by evaluating the degree of defocus in a reconstructed image. To be more precise, an in-focus image in CGI will be obtained if the propagation distance of the patterns in the virtual reference path matches the practical depth of the object, otherwise a defocused image will be reconstructed. This method usually requires forming the images at all the axial locations (the number of the locations: N), which reduces the efficiency of CGI. In this paper, an auto-focusing method is proposed in the deep-Fresnel (DF) region. We present a new iterative algorithm for performing CGI which evaluates reconstructed images based upon deviation-based correlation. We demonstrate that in a given system, an in-focus image of the object and its depth can be obtained in iterations with a depth error ed ≤ δz (δz: longitudinal coherence length of the speckle in the DF region). Compared to the conventional method, this approach improves the convergence speed significantly. We believe our work favors the use of CGI in depth-imaging systems.

Positive and negative correlations in computational ghost imaging for a grayscale object

Our previous work has studied the positive-negative correlations in computational ghost imaging for a binary object. In this work, we focus on the computational ghost imaging system for a grayscale object. We studied the second-order correlation function of this system, and gave the criterion of the positive and negative correlations. Furthermore, this criterion was verified by using numerical simulations.

High frame-rate computational ghost imaging system using an optical fiber phased array and a low-pixel APD array.

To obtain a high imaging frame rate, a computational ghost imaging system scheme is proposed based on optical fiber phased array (OFPA). Through high-speed electro-optic modulators, the randomly modulated OFPA can provide much faster speckle projection, which can be precomputed according to the geometry of the fiber array and the known phases for modulation. Receiving the signal light with a low-pixel APD array can effectively decrease the requirement on sampling quantity and computation complexity owing to the reduced data dimensionality while avoiding the image aliasing due to the spatial periodicity of the speckles. The results of analysis and simulation show that the frame rate of the proposed imaging system can be significantly improved compared with traditional systems.

Analysis of the ‘Anti-scattering’ Capacity of Computational Ghost Imaging System in Solid Scattering Material

Recent researches showed that the traditional ghost imaging (TGI) using pseudo-thermal light can be affected by the solid scattering material placed between the object and the light source. This scattering case might also affect the computational ghost imaging (CGI) and is considered in this paper. Different from the TGI system modeled by Huygens–Fresnel theory in continuous coordinates, in CGI the use of computer-generated patterns with the controllable size ( $d$ ) of each pixel discretizes the object space into the $d$ -based pixel-grids. Therefore, how the CGI system is affected by the scatters depends on the distribution of the scattered light on these discretized grids instead of in continuous coordinates, which has not been explored. In this paper, we demonstrate that the “anti-scattering” capacity of CGI is governed by the discrete point-scattering-function (DPSF) that is determined by $\frac{{w_{0}}}{d}$ ( $w_{0}$ : the width of point-scattering-function of the scatters). We show that the blurry effect on the reconstructed image is visible as $d\ll\frac{{w_{0}}}{2}$ , but can be highly restrained as $d$ increasing to be comparable to $\frac{w_{0}}{2}$ or larger. Furthermore, $d$ determines the spatial resolution power of CGI. In the given CGI system, the minimum $d$ of $\sim\frac{{w}_{0}}{5}$ could be achieved with maintaining the behavior of “scattering-free”.

Optical encryption scheme based on ghost imaging with disordered speckles**Project supported by the National Natural Science Foundation of China (Grant Nos. 61475075 and 61271238) and the Open Research Fund of Key Lab of Broadband Wireless Communication and Sensor Network Technology, Ministry of Education, China (Grant No. NYKL2015011).

An optical encryption scheme based on a ghost imaging system with disordered speckles is proposed to obtain a higher security with a small key. In the scheme, Alice produces the random speckle patterns and obtains the detection results with the help of a computational ghost imaging (CGI) system. Then Alice permutes the order of the random speckle patterns and shares the permutation sequence as a secure key to the authorized users. With the secure key, Bob could recover the object with the principle of the CGI system, whereas, the unauthorized users could not obtain any information of the object. The numerical simulations and experimental results show that the proposed scheme is feasible with a small key, simultaneously, it has a higher security. When the eavesdropping ratio (ER) is less than 40%, the eavesdropper cannot acquire any useful information. Meanwhile, the authorized users could recover completely with the secure key.

High-resolution computational ghost imaging and ghost diffraction through turbulence via a beam-shaping method

Imaging through atmospheric turbulence is a topic with a long history and grand challenges still exist in the remote sensing and astro observation fields. In this letter, we try to propose a simple scheme to improve the resolution of imaging through turbulence based on the computational ghost imaging (CGI) and computational ghost diffraction (CGD) setup via the laser beam shaping techniques. A unified theory of CGI and CGD through turbulence with the multi-Gaussian shaped incoherent source is developed, and numerical examples are given to see clearly the effects of the system parameters to CGI and CGD. Our results show that the atmospheric effect to the CGI and CGD system is closely related to the propagation distance between the source and the object. In addition, by properly increasing the beam order of the multi-Gaussian source, we can improve the resolution of CGI and CGD through turbulence relative to the commonly used Gaussian source. Therefore our results may find applications in remote sensing and astro observation.

Optical image hiding based on computational ghost imaging

Imaging hiding schemes play important roles in now big data times. They provide copyright protections of digital images. In the paper, we propose a novel image hiding scheme based on computational ghost imaging to have strong robustness and high security. The watermark is encrypted with the configuration of a computational ghost imaging system, and the random speckle patterns compose a secret key. Least significant bit algorithm is adopted to embed the watermark and both the second-order correlation algorithm and the compressed sensing (CS) algorithm are used to extract the watermark. The experimental and simulation results show that the authorized users can get the watermark with the secret key. The watermark image could not be retrieved when the eavesdropping ratio is less than 45% with the second-order correlation algorithm, whereas it is less than 20% with the TVAL3 CS reconstructed algorithm. In addition, the proposed scheme is robust against the ‘salt and pepper’ noise and image cropping degradations.

Influence of detector response speed on the contrast-to-noise ratio of reflective ghost imaging

Abstract The influence of detector response speed on the contrast-to-noise ratio (CNR) of reflective ghost imaging (RGI) is studied. To mimic the situation of a slow response detector, the illuminating speckle patterns are replaced with the sum of uncorrelated speckle patterns for each measurement. An expression for the CNR of RGI with added speckle patterns is derived. By employing a light projector to provide spatially incoherent structured illumination in a computational ghost imaging system, we perform computational RGI based on added speckle patterns. The experimental results show that when up to 40 uncorrelated speckle patterns are added together in each measurement, the CNR of computational RGI obtained from 5000 effective measurements remains almost the same as the conventional computational ghost imaging. The reason for this is that the image quality of RGI depends on the kurtosis of intensity fluctuation of speckle field instead of the contrast ratio of speckle pattern. The experimental results agree with the theoretical prediction.

A self-synchronized high speed computational ghost imaging system: A leap towards dynamic capturing

Computational ghost imaging needs to acquire a large number of correlated measurements between reference patterns and the scene for reconstruction, so extremely high acquisition speed is crucial for fast ghost imaging. With the development of technologies, high frequency illumination and detectors are both available, but their synchronization needs technique demanding customization and lacks flexibility for different setup configurations. This letter proposes a self-synchronization scheme that can eliminate this difficulty by introducing a high precision synchronization technique and corresponding algorithm. We physically implement the proposed scheme using a 20kHz spatial light modulator to generate random binary patterns together with a 100 times faster photodiode for high speed ghost imaging, and the acquisition frequency is around 14 times faster than that of state-of-the-arts.

Computational ghost imaging with higher-order cosh-Gaussian modulated incoherent sources in atmospheric turbulence

We show that the resolution of the computational ghost imaging (CGI) system through atmospheric turbulence can be significantly improved by modulating a coherent source with high-order cosh-Gaussian functions. The analytical formula for the CGI system with a higher-order cosh-Gaussian source in turbulent atmosphere is derived and can be viewed as the original object convoluted a point-spread function (PSF). The imaging quality is mainly determined by the size of the PSF, which is closely related to the source parameters of the higher-order cosh-Gaussian beam, the turbulent strength and the propagation distance. Numerical examples are given to clearly see the effects of the above system parameters on the PSF and the quality of the CGI system. Compared with the widely used Gaussian source, it is found that the resolution of CGI can be obviously enhanced by properly adjusting the parameters of the higher-order cosh-Gaussian sources. Thus this kind of shaped source can be used to improve the imaging resolution and may be helpful to the CGI real applications.