Ghost Imaging Research Articles

Underwater environment laser ghost imaging based on Walsh speckle patterns

Underwater imaging is a challenging task because of the effects of scattering and absorption in water. Ghost imaging (GI) has attracted increasing attention because of its simple structure, long range, and achievability under weak light intensity. In an underwater environment, conventional imaging is limited by low sensitivity, resulting in fuzzy images, while ghost imaging can solve this problem. This study proposes underwater laser ghost imaging based on Walsh speckle patterns. According to the simulated and experimental results, noise resistance and a low sampling rate of ghost imaging based on Walsh speckle patterns are proved. As the turbidity of the underwater environment increases, the imaging quality of ghost imaging based on Walsh speckle patterns decreases. However, it remains much better than that of ghost imaging based on random speckle patterns and Hadamard speckle patterns, whereas conventional imaging is no longer distinguishable. Ghost imaging based on Walsh speckle patterns can be performed with a sampling rate lower than 10%, and the peak signal-to-noise ratio and the structural similarity of the results increase by 150.15% and 396.66%, respectively, compared with random speckle pattern ghost imaging. An identifiable image of ghost imaging based on Walsh speckle patterns can be reconstructed with a sampling rate of 6% in a turbid water environment, which is simulated with the concentration of the milk powder not higher than 11.0 g/L. This method promotes the further development of optical imaging technology for underwater targets with a low sampling rate based on ghost imaging.

End-to-end computational ghost imaging method that suppresses atmospheric turbulence.

Images are one of the important sources of getting information, and the process of getting images can be affected by various factors. Atmospheric turbulence is one of them. Ghost imaging has a positive effect on suppressing atmospheric turbulence, but its reconstruction results are not stable, and it cannot get high-quality images under extreme conditions. In this paper, we simulate atmospheric turbulence using a phase screen, combine computational ghost imaging to simulate the imaging process, and analyze the factors that affect the imaging. We use an end-to-end neural network to input the bucket signal into the network after processing, which can not only reconstruct the target image directly but also save reconstruction time by removing the process of correlation calculation. Simulations show that good reconstruction results can be obtained at low sampling rates and extreme conditions.

Bipolar compressive ghost imaging method to improve imaging quality.

Compressive ghost imaging (CGI) can effectively reduce the number of measurements required for ghost imaging reconstruction. In most cases, however, when using illumination patterns as measurement matrices, CGI has not demonstrated the ability to reconstruct high-quality images at an ultra-low sampling rate as perfect as claimed by compressive sensing theory. According to our analysis, the reason is that the non-negative nature of light intensity causes measurement matrix in compressive ghost imaging to be inconsistent with the essential requirements of good measurement matrix in compressive sensing theory, leading to low reconstruction quality. Aiming at this point, we propose a bipolar compressive ghost imaging method to improve the reconstruction quality of ghost imaging. The validity of the proposed method is proven by simulations and experiments.

Principle of subtraction ghost imaging in scattering medium

Scattering medium in light path will cause distortion of the light field, resulting in poor signal-to-noise ratio (SNR) of ghost imaging. The disturbance is usually eliminated by the method of pre-compensation. We deduce the intensity fluctuation correlation function of the ghost imaging with the disturbance of the scattering medium, which proves that the ghost image consists of two correlated results: the image of scattering medium and the target object. The effect of the scattering medium can be eliminated by subtracting the correlated result between the light field after the scattering medium and the reference light from ghost image, which verifies the theoretical results. Our research may provide a new idea of ghost imaging in harsh environment.

Improving the quality of panoramic ghost imaging via rotation and scaling invariances

Panoramic ghost imaging (PGI) is a novel method for enlarging the field of view (FOV) of ghost imaging (GI), allowing for the practical application of GI. However, the imaging resolution is limited because of the hardware technology. To achieve the coexistence of high resolution and large FOV of GI, the sub-cell pattern shifting method (SCPS) based on the rotation and scaling invariances (RSI) of the log-polar annular pattern structure is proposed to reconstruct higher-resolution PGI from the panoramic ghost images with sub-pixel shifting. Results show that the SPCS can improve the resolution of PGI with the same total number of measurements and reduce the noise to ensure that the PGI with high-quality can be obtained. This method provides a potential way to promote the practical application of GI with high quality and large FOV.

Optical encryption for multi-user based on computational ghost imaging with Hadamard modulation

In multi-user applications, one of the thorny problems for a cryptographic algorithm is how to distribute the keys and reduce the amount of transmitted data without crosstalk and security risks. Based on Hadamard modulated Computational Ghost Imaging (CGI), we propose an optical encryption scheme for multi-user, in which a common ciphertext is public for all users and one user owns a unique key to index the row sequence of Hadamard basis for decryption. Therefore, the channel resources are saved because the ciphertext does not need to be transmitted. Compared with the conventional CGI-based random intensity modulation encryption, the scheme not only reduces the amount of transmitted key data but also enhances the quality of decrypted images, which benefits from the order of Hadamard basis rather than its distribution being taken as the key. Theoretical analysis and numerical simulations are conducted to prove the feasibility and property of the scheme.

Equivalence analysis of Fourier ghost imaging and sinusoidal ghost imaging

Ghost imaging, also known as correlation imaging, is one of the research hotspots in the imaging field. Various ghost imaging systems with different basic principles and implementation architectures have emerged, but the correlation between them is weak, showing a diversified trend and recent research progress is slower than before. Studying the essence of ghost imaging theory is a feasible direction to explore the unknown field of ghost imaging. Through research, we find that Fourier ghost imaging and sinusoidal ghost imaging are based on the same type of orthogonal sine speckle and cosine speckle, which have a very high similarity. At the same time, sinusoidal ghost imaging method can give a complete spatial description and spatial imaging process, so we guess that these two imaging methods can reveal the relationship between spatial imaging and Fourier domain imaging. On this basis, it is proved that Fourier ghost imaging and sinusoidal ghost imaging are equivalent in principle. The former can be realized by n-step phase shift, while the latter can be equivalent to two-step phase shift. Considering that both of these methods use sine and cosine fringes as structural speckles. By combining the spatial decomposition characteristics of sine speckle imaging, the relationship between structural speckle imaging and traditional ghost imaging is analyzed, and the principles of some methods constructed on the basis of these two methods are explained. The simulation results applied to edge detection show that the combination of the two methods can simultaneously obtain the better anti-noise performance of Fourier ghost imaging and the higher imaging efficiency of sinusoidal ghost imaging. Since sinusoidal ghost imaging relates the characteristics of image spatial decomposition to traditional ghost imaging, and their expression is equivalent to the expression of orthogonal Fourier transform domain of Fourier ghost imaging, the association of ghost imaging methods in Fourier domain and even in the whole orthogonal transform domain and spatial domain can be generalized. This conclusion may provide a way for associating different kinds of ghost imaging, and it can be hoped that more and more new types of ghost imaging systems will be developed.

Spontaneous four-photon mixing in ghost imaging

A generalization of the calculation of the formation of ghost images in the course of backward four-photon mixing to the real situation of non-planar spatially limited pumping, which has a Gaussian profile of the fundamental laser mode, is developed, taking into account the specifics of the formation of phantom images. Computer images have been obtained that make it possible to estimate the spatial resolution of the systems. A relatively simple equivalent scheme for describing the process is proposed, which shows that the effect of diffraction in nonlinear systems is similar to its role in ordinary linear optics with a limited aperture. A fiber-optic version of the formation of ghost images is proposed, suitable for the study of hard-to-reach cavities and organs of the human body, which allow the introduction of a thin fiber bundle there. Keywords: quantum entangled states, quantum images, optical systems, ghost images, quantum measurements.

STUDY OF SECURITY FEATURES PRESENT IN NEPALI PASSPORT

Security features present on Nepali passport are examined with the help of Video Spectral Comparator. Mainly examination is carried out with application ultra-violet light, normal light, oblique light and transmitted light. We obtain different types of security features including florescence, ghost image, binding thread, optical fiber, punched number, barcode, micro-printing, watermark, emboss etc. The main aim of this work is to provide information about security features present in Nepali passport so that concern agencies as well as general public to distinguish between genuine and fake passport.

Ghost Imaging by Single-Layer Neural Network Based on Forward Physical Model

Ghost Imaging by Single-Layer Neural Network Based on Forward Physical Model

Computational Ghost Imaging with the Human Brain

Brain–computer interfaces are enabling a range of new possibilities and routes for augmenting human capability. Here, we propose brain–computer interfaces as a route towards forms of computation, i.e., computational imaging, that blend the brain with external silicon processing. We demonstrate ghost imaging of a hidden scene using the human visual system that is combined with an adaptive computational imaging scheme. This is achieved through a projection pattern “carving” technique that relies on real-time feedback from the brain to modify patterns at the light projector, thus enabling more efficient and higher-resolution imaging. This brain–computer connectivity demonstrates a form of augmented human computation that could, in the future, extend the sensing range of human vision and provide new approaches to the study of the neurophysics of human perception. As an example, we illustrate a simple experiment whereby image reconstruction quality is affected by simultaneous conscious processing and readout of the perceived light intensities.

Спонтанное четырехфотонное смешение в формировании фантомных изображений

A generalization of the calculation of the formation of ghost images in the course of backward four-photon mixing to the real situation of non-planar spatially limited pumping, which has a Gaussian profile of the fundamental laser mode, is developed, taking into account the specifics of the formation of phantom images. Computer images have been obtained that make it possible to estimate the spatial resolution of the systems. A relatively simple equivalent scheme for describing the process is proposed, which shows that the effect of diffraction in nonlinear systems is similar to its role in ordinary linear optics with a limited aperture. A fiber-optic version of the formation of ghost images is proposed, suitable for the study of hard-to-reach cavities and organs of the human body, which allow the introduction of a thin fiber bundle there.

Computational Ghost Imaging Method Based on Discrete W Transform

Computational Ghost Imaging Method Based on Discrete W Transform

Trend of action on the display effect based on Pepper’s ghost images affected by illumination and color temperature from led light sources

Trend of action on the display effect based on Pepper’s ghost images affected by illumination and color temperature from led light sources

Sampling Rate Setting in Convolutional Neural Network Ghost Imaging

Sampling Rate Setting in Convolutional Neural Network Ghost Imaging

Optimization method of Hadamard coding plate in γ-ray computational ghost imaging

Optimization method of Hadamard coding plate in γ-ray computational ghost imaging

Optimized Reconstruction of Computational Ghost Imaging Based on Image Fusion

Optimized Reconstruction of Computational Ghost Imaging Based on Image Fusion

An MTF calculation model under the influence of ghost images

An MTF calculation model under the influence of ghost images

Tuning of the Stokes scintillations by controlling the longitudinal coherence

Various imaging techniques such as optical coherence tomography (OCT) and ghost imaging focus on increasing the resolution of the system to enhance the imaging quality. The information of polarization fluctuations of the field can reveal the fine details of the source or object through Stokes correlations. In this study, we provide a framework for the correlation in the fluctuations of Stokes parameters in the longitudinal direction for the general non-collimated fields. We first derive the four scintillation coefficients for a scheme using Gaussian statistics, which are basically the variance of the Stokes parameters. The influence of longitudinal spatial coherence (LSC) and temporal coherence on tuning the scintillation coefficients can be useful in purposely managing the noise of a Stokes parameter. Experimental demonstration of the modulation of the scintillation coefficients owing to frequency and angular spectrum endorse the theoretical findings. The temporal dependence of the Stokes correlations is used to trace the evolution of the polarization of the system. Ghost imaging exploiting the LSC for better resolution can be benefited from the dependence of Stokes scintillation on the angular spectrum width. Moreover, encoding based on dynamical polarization fluctuations can utilize the knowledge of Stokes correlations.

Time‐Efficient Object Recognition in Quantum Ghost Imaging

AbstractAcquiring information at the fastest possible rate is often desirable, particularly in quantum ghost imaging which suffers from slow reconstruction speeds. Many computationally intense deep‐learning methods have been implemented in an effort to speed up image acquisition times by retrieving image information. Often over‐looked, machine learning methods can offer the same, if not better, speed up in image acquisition time by an object recognition process. Four machine learning algorithms are implemented and trained on a uniquely generated, noised, and blurred dataset of numerical digits 1 through 9. Of the tested recognition algorithms, logistic regression shows a 10× speed up in image acquisition time with a 99% prediction accuracy. Additionally, this reduction in acquisition time is achieved without any image denoising or enhancement prior to recognition, thereby reducing training and implementation time, as well as the computational intensity of the approach. This method can be implemented in real‐time, requiring only 1/10th of the measurements needed for a general solution, making it ideal for quantum imaging and recognition of light sensitive structure.