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In recent years, Janus microspheres technology has been widely applied and developed in various fields. However, existing studies often rely on electron microscopy images, treating Janus microspheres as spherical to observe their submicron structures. This approach falls short in meeting the demand for precise measurement of the specific position and orientation of microspheres at the single-molecule scale. Here, we propose a standardized processing procedure that integrates multiple image processing algorithms to measure the position of Janus microspheres through the image capture. Our approach enhances the two-dimensional planar positioning accuracy of non-spherical Janus microspheres in micro-nano optical measurement systems. Utilizing this method, we can conduct a further research on the structure and motion characteristics of the microsphere at the single-particle scale. This method has been validated on a transmission illumination optical tweezers platforms, successfully calibrating the central position of the optical trap. Our work offers a greater convenience for measuring non-spherical Janus microspheres in liquid environments. It also provides a fresh perspective for subsequent studies on the motion trajectories and force dynamics of heterogeneous microspheres, showcasing its broad potential for application. • A standardized image processing procedure is proposed. • 2D positioning accuracy for non-spherical Janus microspheres is improved. • Controllable rotation of Janus microspheres with varying sizes and ratios is measured. • Research lays groundwork for Janus microspheres in single-molecule applications. [ABSTRACT FROM AUTHOR]

Fusion of information from infrared and visible images from different modalities has always been a hot research topic in the field of image processing. In order to solve the problem that existing fusion methods cannot fully utilize the deep information of images, this paper proposes a fusion algorithm DAE-Nest based on depth information extraction and enhancement. The algorithm consists of encoder-feature enhancement-fusion layer-decoder modules for unsupervised learning. At first, the improved coding structure is used to extract multi-scale features of the source image; secondly, the extracted features are data enhanced to fully utilize the deep image information; then, the enhanced features are fused according to the corresponding fusion strategy; finally, the decoder takes the input of fused features and reconstructs them into an information-rich fused image. DAE-Nest was subjected to corresponding fusion test experiments on the TNO and RoadScene data sets respectively and compared with 9 excellent fusion algorithms. In terms of subjective evaluation, DAE-Nest can make full use of the deep information in the source image, and the generated fusion image also conforms to the visual perception of the human eyes; in terms of objective evaluation indicators, DAE-Nest's average gradient and spatial frequency on the TNO data set, it achieved the best performance in the three evaluation indicators of structural similarity and structural similarity, and also achieved the best performance in the fusion quality evaluation index on the RoadScene data set. Therefore, the fusion method proposed in this paper has achieved excellent results both subjectively and objectively, and can effectively fuse infrared and visible images, laying a good foundation for subsequent visual tasks. • Design a deep multi-scale feature extraction structure to fully extract the deep scale features of the image. • Design feature enhancement structures to make full use of the deep scale features of the image. • Design end-to-end integration modules IRS (Inception ResNet Shallow) and IRD (Inception ResNet Deep). • The proposed method was evaluated on two test sets and good fusion results were achieved. [ABSTRACT FROM AUTHOR]

Satellite Laser Ranging (SLR) data are typically pre-processed involves the manual screening method. However, this methodology heavily depends on the interpreter's expertise, potentially leading to concerns regarding decreased detection efficiency, limited automation, and sluggish processing speeds. This study introduces an automated processing approach using image denoising techniques. It involves deriving binary images from raw SLR point cloud data, employing a median filter to remove noisy data, and generating SLR normal points automatically for accurate and efficient data processing. Theoretical and experimental results reveal that the proposed method exhibits an efficient echo data recognition rate exceeding 80%, while maintaining a low misdetection rate of 1% or less. The proposed method offers a superior alternative to manual screening, capable of processing SLR data in batches, which fulfilling the future need for efficient automation and management of massive SLR datasets. [ABSTRACT FROM AUTHOR]

Metasurface-based optical differentiators have recently attracted attention for their potential advantages in real-time and high-throughput image processing technology. However, the existing differentiators suffer from limitations in numerical aperture (NA). Here, we propose a differential metasurface based on silicon clusters covered with polydimethylsiloxane, achieving a remarkable NA of 0.7. We numerically demonstrate the proposed differentiator can perform second-order differentiation on a 1D spatial function and high NA can accurately compute smaller-scale variations. We further demonstrate its ability to achieve edge detection on 2D images. Our results advance the development of ultra-high numerical aperture optical differentiator and provide new opportunities for image processing. [ABSTRACT FROM AUTHOR]

Optical differentiation plays a pivotal role in analog computing and image processing, owing to its faster operating speeds and lower power consumption. However, the conventional differentiator encounters a common issue of single and fixed functions due to the lack of effective dynamic modulation means. Here, we proposed a polarization-sensitive differentiator based on a Fano resonance metasurface. The interference between transmitted light and a quasi-guided mode induces Fano resonance, resulting in the leakage of high-frequency component of the p-wave. By adjusting the asymmetry and line width of the Fano resonance line shape, the metasurface can function as a Fourier spatial filter to achieve the differential of an incident beam. Additionally, the direction of the s- and p-wave can be controlled to realize multiple differential functions. We demonstrate the simulation of switchable differential between arbitrary one-dimensional (1D) direction and two-dimensional (2D) directions, with a numerical aperture up to 0.26. It is expected that this switchable optical differentiator will have broad applications in areas such as bioimaging and computer vision. • A dynamic switching between 1D and 2D state differentiator based on an optical metasurface was proposed. • This method requires only a tiny metasurface to achieve an optical differentiator that can dynamically adjust the direction of the differential. • We introduce the s- and p-wave bases and the Fano resonance effect to make the differential function of the metasurface polarization-dependent. • The differentiator shows numerical aperture up to 0.26. [ABSTRACT FROM AUTHOR]

We propose an optical Laplace operator consisting of a large-focal-length Pancharatnam-Berry lens placed on the Fourier plane of an optical imaging system and sandwiched with two orthogonal linear polarizers. Theoretical analysis reveals that the isotropic second-order differentiation derives from the quadratic phase attached to the left-handed and right-handed circularly polarized light. The Pancharatnam-Berry lens made of liquid crystal with high transmittance and diffraction efficiency is integrated into different imaging systems to realize edge detection for both amplitude and phase objects, and the results conform to the theory well. This work paves the way to implement Laplace operator in practical applications such as image processing and high-contrast microscopy. • The optical Laplace operator is realized using Pancharatnam-Berry lens of large focal length and two orthogonal polarizers. • The liquid-crystal PB lens of focal length 40 m is fabricated and has high transmittance and diffraction efficiency. • The experimental imaging results based on the proposed setup conforms to theory well. • The work paves the way to the applications of optical Laplace operator in image processing and high-contrast microscopy. [ABSTRACT FROM AUTHOR]

In this paper, a joint baud-rate and modulation format identification (BR-MFI) is proposed based on asynchronous delay tap picture (ADTP) analyzer by using convolutional neural network (CNN). Considering 8 types of signals under different channel conditions of OSNR, CD and DGD, the proposed BR-MFI can achieve 100% accuracy after 6 training epochs, and just 2 epochs for MFI. Here, two test number of samples are about 15% of total samples. This paper also investigates the influence of CNN structure on the identification accuracy. The results show that CNN has better performance for image processing than back-propagation Artificial Neural Network (BP-ANN). [ABSTRACT FROM AUTHOR]

In this paper, a scalable asymmetric image compression and encryption method is proposed based on discrete wavelet transform (DWT) and nonlinear operations in the cylindrical diffraction domain. In this scheme, the grayscale image is processed by a DWT, and four component images are obtained. Then single amplitude ciphertext is obtained by nonlinear operation of phase truncation after cylindrical diffraction. Since the reconstruction from the four component images of DWT is scalable, the proposed method also has scalability. Moreover, the proposed method has high security because it can resist the phase-retrieval attack and prevent information disclosure. Numerical simulations have demonstrated the security and effectiveness of the proposed method. • A scalable encryption with three models for different effects and scenarios. • Free of phase-retrieval attack and information disclosure. • A high quality of the decrypted image due to the recovered high-frequency information. [ABSTRACT FROM AUTHOR]

Photon echo technique based on rare earth ion-doped crystal has potential applications in optical signal processing. However, the coexistence of different types of photon echo lead to a great reduction of signal-to-noise ratio (SNR). Noncolinear scheme can be adopted to improve SNR by separating such echo signals in the space domain. In this paper, by using the noncolinear beam configuration, we present a detailed analysis and characterization of the accumulated photon echo signals based on rare earth ion-doped crystal. Accumulated photon echo signals occurred at different moment can be analytically predicted using Cayley–Klein parameters method, which is confirmed with the numerical results by solving the Maxwell–Bloch equations. The performance of the spatial-spectral grating has been evaluated, including the grating period, grating amplitude and grating shape. Finally, in the case of noncolinear configuration, the influence parameters related to echo signal intensity has also been discussed compared with the collinear geometry. The results presented here may be helpful to gain new insights on the typical parameters for optical signal processing by using photon echo technology. [ABSTRACT FROM AUTHOR]

Recently, laser speckle contrast analysis (LASCA) technology has spurred the exploration to instantly visualize microcirculatory tissue blood perfusion in clinical diagnosis, due to its non-contact, non-invasive and rapid imaging advantages. However, traditional medical imaging systems used to perform laser speckle contrast imaging (LSCI) are expensive and their transportation needs prudence, limiting the wide availability of LASCA for personal preliminary diagnosis. In this article, a low-cost, lightweight and portable smartphone-based laser speckle contrast imaging (smartphone-LSCI) is proposed to address this issue. With a built-in image sensor and powerful computational capability of the smartphone, the proposed system could be utilized to estimate the speckle contrast of human skin under various conditions and obtain information of the blood flow velocity of capillaries along with the degree of blood perfusion. Through experiments and theoretical analysis, we systematically studied the feasibility and robustness of image sensors on smartphones-LSCI. Experiments prove that ambient light has little influence on the performance of our smartphone-LSCI. In addition, the speckle image processing flow of smartphone-LSCI is proposed, together with an enhanced spatial LASCA (esLASCA) method. In the experiments with a low-cost smartphone, i.e., Redmi K40, the 4000 × 3000 pixels images can be processed at a frame rate of 20Hz. The consumption time of both the existing state-of-the-art roll algorithm and the proposed esLASCA is linearly proportional to the width (height) of the image resolution. However, our proposed method shows a slower growth rate and lower computational time when the window size is small. [ABSTRACT FROM AUTHOR]

For controlling the visibility of the Lau patterns, we disclose the use of a zoom system that implements a zero-throw, tunable magnification of the source grating. The zoom system implements a nonmechanical technique, for controlling the in-register condition of the Lau patterns. We show that one can increase the sharpness the Lau fringes, by exploiting the noncyclic autocorrelation of the Fourier coefficients, associated to the grating acting as spatial filter. The described technique can be thought of as a frequency sweeping technique, which tunes the visibility and the shape of the Lau fringes. • Controlling Fringe Visibility in the Lau Effect. • Varifocal Lenses for Magnifying the Source Grating. • Noncyclic Autocorrelations of the Barker Sequences. • Autocorrelation Coefficients for sharp fringes. [ABSTRACT FROM AUTHOR]

Abstract Optical microscopy is believed to be an efficient method for identifying layer number of two-dimensional (2D) materials. However, since illuminants, cameras and their parameters are different from lab to lab, it is impossible to identify layer numbers merely by comparing a given optical image with standard or calculated images under standard conditions. Here we reported an image reconstruction method, converting raw optical images acquired by arbitrary illuminants and cameras into reconstructed images under the condition of specified illuminant and specified camera. After image reconstruction, the color differences of each layer number roughly equaled those calculated under the specified condition. By comparing the color differences in the reconstructed image with those calculated under the specified condition, the layer numbers of 2D materials in our lab and published papers, including MoS 2 , WS 2 , and WSe 2 , were unambiguously identified. This study makes optical microscopy a precise method to identify layer numbers of 2D materials on known substrates. [ABSTRACT FROM AUTHOR]

Abstract The resolution of traditional fluorescence microscopy is limited due to the optical diffraction. Various techniques have been developed to surpass the diffraction limit in recent years. Among these methods, nonlinear structured illumination microscopy (nonlinear SIM) is able to provide fast imaging speed, wide field of view and considerable resolution enhancement simultaneously. However, the current developed nonlinear SIM approaches have their own defects. We report a potential better nonlinear SIM for live-cell imaging termed 'Matrix STED-SIM' with patterned illumination based on both structured excitation grid and stimulated emission depletion (STED) grid. Theory and simulation analysis are presented for illustrating the feasibility of our method to achieve better super-resolution imaging than other current approaches. In addition, we demonstrate the robustness and potential practicability of this new method considering the impact of image noise and exposures. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a new quantum representation model of color digital images (QRCI) is investigated, in which the color information is encoded by the basis states of qubit sequences. QRCI model utilizes 2 n + 6 qubits to store a color digital image with size 2 n × 2 n. Compared with the existing NCQI representation model, the storage capacity of QRCI improves 2 18 times. Moreover, some quantum color image processing operations concerning channels and bit-planes based on QRCI are discussed and their quantum circuits are designed. Comparison results of the quantum circuits indicate that these operations based on QRCI have lower quantum cost than NCQI. Therefore, the new proposed QRCI representation model can save more storage space and it is more convenient to conduct quantum color image processing operations concerning channels and bit-planes. This work will help the researchers to further investigate more complex quantum color image processing operations based on QRCI. [ABSTRACT FROM AUTHOR]

Abstract Underwater imaging is attractive but challenging. Images could be severely degraded by the particles in turbid water because of backscatter generation and signal light attenuation. In this paper, we focus on the scheme of underwater imaging and study the methods of visibility enhancement of turbid underwater images based on polarimetric imaging utilizing active unpolarized illumination. Compared with traditional polarimetric imaging using linearly polarized illumination, using unpolarized illumination ensures the polarization effect of the signal light could be neglected, no matter the depolarization degree of the object is high or low, which expands the application range of underwater polarimetric imaging and makes the underwater polarimetric imaging scheme more reliable and robust. Experimentally, the visibility and the contrast of underwater images are enhanced effectively. In addition, it is demonstrated that our method is applicable for objects of different materials and different imaging distances in turbid water. The contrast of underwater images could be promoted at least 100%, meaning that this kind of technique can be potentially used in many underwater environments. [ABSTRACT FROM AUTHOR]

Abstract We propose and experimentally demonstrate an adaptive image restoration method based on constrained least squares filtering (CLS) and noise level estimation by principal component analysis of low-rank patches (PCA) that enhances the signal-to-noise ratio (SNR) of Brillouin optical time domain analysis sensor (BOTDA). The proposed method employs PCA to estimate the initial noise level of the sensing image and subsequently the input parameter for CLS can be adjusted by a constraint factor. Furthermore, to effectively remove the noise in the raw data, we introduce a calculation procedure for which the noise level of the denoising image serves as a criterion. This procedure is adaptive and can restore the optimal Brillouin gain spectrum. In the experiment, the proposed method shows an increase of 12.2 dB in SNR and that the temperature accuracy can be increased to 1.3 °C. The adaptive CLS is also applied to sensing data with the different noise level, which validates that this method is a valid denoising technique. This report describes that image restoration, including non-local means, wavelet filter and CLS, has been applied to conventional BOTDA with the spatial resolution of 1m. Due to the influence of linewidth broadening for a 10 ns pulse, these methods all show sub-meter distortion in resolution, whereas the proposed method has the least impact on the spatial resolution with 1.41m. The proposed method is adaptive and can provide faster processing speed; thus it can be considered to be an alternative technique to enhance the performance of distributed optical fiber sensors, especially for long-distance and high-resolution sensing. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a speckle noise suppression method employing time multiplexing in holographic display is proposed. The recorded object is separated into object point groups by pixel separation. For each object point group, some phase-only subcomputer-generated holograms (sub-CGHs) with independent initial random phases are generated. In the reconstruction process, a spatial light modulator (SLM) is used to load the sub-CGHs. The reconstructed image is generated through time multiplexing technology. Meanwhile, the speckle noise of the reconstructed image is reduced effectively by averaging the speckle noise and separating the adjacent image points in space. Compared with the pixel separation method, both simulation and optical experiments are carried out to confirm that the proposed method suppresses the speckle noise effectively with less computation burden. [ABSTRACT FROM AUTHOR]

Abstract A phase recovery method from a single fringe pattern with closed fringes is developed. The interferogram is first normalized and then rotated to create a new fringe pattern. Both interference images are multiplied which results in the sum of the cosines of the symmetric and asymmetric components of the phase respect to the rotating axis. If the original phase contains tilt and also possesses a high degree of symmetry respect to the rotating axis, the cosine of the asymmetric term will be composed of tilt and a small asymmetric term. In this case, the Fourier transform of the multiplication will be given by two high intensity peaks localized symmetrically respect to the origin and a broader lobule centered at the origin. The asymmetric component of the phase is then recovered with a Fourier method and used to calculate the phase of the original interferogram. The above procedure may serve as an alternative to other methods that works iteratively to recover the phase from a single interferogram with closed fringes as it is demonstrated in experimental and simulated data. [ABSTRACT FROM AUTHOR]

Abstract Optical imaging systems with extended depth of field based on wavefront coding can be used in many fields, which require more object information along the optical axis in a snapshot. When using the non-rotational symmetric phase masks such as cubic phase mask, the final images are usually restored by classical wiener restoration method. However, the existence of image artifacts in final restored images is a problem to be solved. We proposed a method to alleviate the image artifacts by processing two conjugate images, which are captured by image sensor before and after rotating the phase mask 180 degrees along the optical axis. Unlike the previous methods usually need to measure the point spread function or optical transfer function of the imaging system, we do not need to measure them anymore. Both the ZEMAX simulation and experiment verified our method. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we propose an approach to optically refocus a large-depth three-dimensional (3D) scene on its real depth based on the reprojected parallax images. In the refocusing approach, the parallax images only related to the specific depth can be generated without black zone by reprojecting the captured parallax images. The elemental image array for the same depth can be obtained simply. Therefore, a high-quality refocusing of the 3D object at arbitrary depth can be achieved. The homography matrix used for reprojection contains both the calibration parameters of the camera array and the pixel shifting value related to the specific depth. Experiments on real-world scene are carried out and the results validate the feasibility of our proposed method. [ABSTRACT FROM AUTHOR]

Abstract A layered rendering method for generating computer-generated hologram (CGH) of 3D objects based on view volume transformation is presented. The shape distortion and the size deviation of the 3D reconstructed image existing in conventional layer-based methods are avoided, and the reconstructed 3D image can preserve the real size of the original model with high quality. Real-time interaction with the digitally reconstructed holographic image with clear depth cues is experimentally demonstrated. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a joint symbol-scrambling and chaotic discrete Fourier transform (DFT) precoding scheme is proposed for orthogonal frequency-division multiplexing (OFDM) visible light communication (VLC) systems for encrypted image data. In the proposed scheme, the original image data is first divided into sub-blocks and then an inter-block scrambling operation is applied to the resulting image data. Secondly, the real and imaginary parts of the transmitted QAM symbols are encrypted using two separate chaotic sequences generated from different chaotic maps. Thirdly, the resulting encrypted QAM signals are transformed into new signals using a chaotic DFT-precoding matrix in order to further improve the security and bit error rate (BER) performance of the OFDM signals. The mathematical model of our proposed encrypted OFDM-based VLC system is established and the BER formula is derived. The obtained BER formula is confirmed by our simulation results. Our simulation results also show that both symbol scrambling and image-block scrambling have no effect on the BER of the proposed DFT-precoded OFDM-based VLC system. The proposed scheme not only improves the quality of the transmitted image but also protects the transmitted image data from eavesdroppers. Highlights • A Joint image encryption and chaotic DFT precoding was proposed in OFDM VLC to enhance the security. • The formula of BER of the proposed system is derived and its validity is verified by simulation. • The proposed scheme can both achieve reducing PAPR and improving BER performance. [ABSTRACT FROM AUTHOR]

Abstract In this paper, an asymmetric multiple-image encryption algorithm based on compressed sensing and cylindrical diffraction is proposed. Firstly, these multiple gray scale images are compressed by compressed sensing in separately. Then single amplitude ciphertext is obtained by asymmetric operation of phase truncation after cylindrical diffraction. This method not only can achieve multiple-image encryption with a small amount of data, but also can prevent information disclosure. Moreover, the proposed method has high security because it can resist the phase-retrieval attack. Numerical simulations have demonstrated the security and effectiveness of the proposed method. Highlights • Free of phase-retrieval attack and information leakage • First time to apply the cylindrical diffraction to optical multiple-image encryption • Partly solved the problem of large amount of data in the multi-image encryption • Large encryption capacity of encrypting up to eight images [ABSTRACT FROM AUTHOR]

We report a reconfigurable microwave photonic mixer with multiple functions and wide bandwidth. By changing the photodetection configuration, the mixer can be conveniently reconfigured to realize four functions: single-ended mixing, I/Q mixing, double balanced mixing and image rejection mixing. Furthermore, the filter-free system has a wide bandwidth and the ability to perform both frequency up-conversion and down-conversion. The proposed reconfigurable mixer is based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). The optical signal is modulated by the DP-DPMZM and split into two orthogonally polarized signals, which are combined by a 90° optical hybrid and detected by photodetectors. The experimental results show that the mixer has a wide bandwidth from 2 GHz to 30 GHz with a 30 dB spur suppression, and the image rejection ratio of the image rejection mixer is over 30 dB. [ABSTRACT FROM AUTHOR]

This paper proposes a Hash based authentication scheme that employs equal modulus decomposition (EMD) and fractional joint transform correlator. An 8-bit grey scale image is separated into its constituent bit plane matrices. Each bit plane matrix is subjected to EMD encryption procedure employing numerically generated random phase mask (RPM) and amplitude mask (AM). The EMD encryption results into two complex functions, which are used for the generation of phase mask and amplitude mask for the next bit plane matrix. A two round EMD procedure is carried out to obtain an 8-bit intensity matrix which is Fourier transformed and its central frequency components are extracted to obtain a 256-bit Hash value. Numerical simulations have been carried out to validate the effectiveness and performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, we propose a simple, novel method to suppress background noise in confocal scanning fluorescence microscopy images with superoscillations. The proposed method retains high resolution, while completely removing superoscillation sidebands. Simulations of images from conventional confocal scanning microscopy, superoscillations, and the proposed method are presented, demonstrating its effectiveness. [ABSTRACT FROM AUTHOR]

A non-periodic sample, which also contains a periodic structure with a period smaller than the resolution limit of the optical microscope used for imaging it, was illuminated with the cone of white-light produced by a ring-shaped condenser with a numerical aperture larger than the objective lens. By rotating a slit placed at the back focal plane of the objective lens, we obtained several pairs of real plane and Fourier plane images corresponding to different diffraction directions. We simulated, discussed, and demonstrated a numerical algorithm capable of producing a high-resolution image of the sample after processing the experimental images. [ABSTRACT FROM AUTHOR]

Based on compressed sensing theory and TDI CCD driving mode, a collaborative coding method founded on TDI CCD charge transfer and random exposure is proposed in this paper, which breaks through the limitation of pixel size and achieves the improvement of one-dimensional image resolution. By extending this method, an orthogonal dual detector super-resolution imaging system is established, which realizes the improvement of two-dimensional image resolution. Further, the convex optimization algorithm and the proportional fusion algorithm are proposed as the two-dimensional image fusion algorithm. Theoretical modeling and simulation results demonstrate the effectiveness of the proposed imaging method and system, which provide an innovative approach of system implementation for super-resolution imaging based on compressed sensing theory. [ABSTRACT FROM AUTHOR]

We propose an optical encryption method allowing the parallel encryption and hierarchical retrieval for multi-channel images based on a joint Fresnel transform correlator. In our designed scheme, the linear phase shift operation for the phase masks is utilized to achieve the aim of ensuring that the center of the complex amplitude distributions from the same group can overlap with each other in Fresnel domain, and the phase retrieval algorithm for designing the phase masks is used to avoid the cross talk between multi-channel images. The optimized phase masks can be flexibly reconfigured on the spatial light modulator without increasing the additional optical hardware and system complexity. Our designed scheme can encrypt multi-channel images simultaneously into a single cipher-text, which can also be used to recover arbitrary original images with corresponding keys. Thus, this method can achieve the aim of the hierarchical retrieval of encrypted images from a single cipher-text. Moreover, because the encryption process does not require any transformative lenses and accurate alignment of optical elements, the encryption scheme is easy to be optically implemented. Furthermore, compared with the previous JTC-based cryptosystems, the Fresnel diffraction distance and the position of the key masks in our proposed scheme can both be utilized as the additional encryption keys, which can enhance the security effectively. The theoretical analysis and numeric simulation results both validate the feasibility and effectiveness of the designed scheme. [ABSTRACT FROM AUTHOR]

Although the speckle noise in hologram reconstructed image can be effectively suppressed by averaging multiple reconstructions with different speckle patterns, the approach usually needs a lot of the reconstructions and encounters an improvement limit. In this paper, we propose a speckle noise suppression method that combines averaging several reconstructed images and a modified non-local means (MNLM) filtering method. First, the probability density function (PDF) of the averaged speckle field after averaging multiple hologram reconstructions is deduced, then the number of hologram reconstructions for the averaging process is inferred for making the speckle noise distribution approaches Gaussian distribution. Second, considering the statistical model of the multiplicative Gaussian noise, we modify the NLM filtering for effectively removing the residual noise in the averaged image. The experimental results show that the proposed method can reduce the speckle noise more than 90% and achieve nearly speckle-free. Compared with another similar method, the presented method is more effective and feasible to suppress speckle noise and preserve image contrast based on a small number of reconstructions. [ABSTRACT FROM AUTHOR]

A new type of optical in-line holographic three-dimensional (3-D) video display system with omnidirectional viewing zones by using a center-symmetric multi-sideband filtering method is proposed. The frequency spectrum of the complex hologram is center-symmetrically divided into even numbers of multi-sidebands and partitioned into two groups by being alternately selected along the angular direction. One group corresponding to the conjugate image is filtered out in both of the digital-recording and optical-reconstruction processes with their specific filter masks. Then, from the other group, the real image, which can be viewed from almost all directions with a set of angularly-subdivided viewing zones, is reconstructed on the optical 4- f lens system without a conjugate image. Fourier-optical analysis and experiments with 3-D objects in motion confirm the feasibility of the proposed system. [ABSTRACT FROM AUTHOR]

Computational ghost imaging (CGI) presents a new way to solve the problem of extended depth of field (DOF), which has been studied for a long time. The application of correlation theory confirms that a plane light source can be used to avoid the limitation of DOF in CGI. Results from experiments where real objects are imaged by CGI between 0.3 m and 1.2 m verify that images are consistent in quality. This confirms that CGI is not affected by DOF and can be used to improve the accuracy of integral and microscopic imaging. [ABSTRACT FROM AUTHOR]

Continuous-wave terahertz digital holography is a practical tool to obtain the complete wave-front information of a sample in the terahertz region that has offered unique advantages in various fields. The propagation distance plays a decisive role in the numerical reconstruction of both in-line and off-axis digital holograms. Only when a terahertz hologram is propagated back to a focal object plane can the authentic amplitude and phase distribution be reconstructed, which is actually a troublesome task. In this manuscript, the combination of hologram enhancement, spectrum filtering, phase retrieval and phase unwrapping algorithms is illustrated and organized to benefit the decision-making process of the autofocusing method not only for the amplitude distribution but also for the phase image. To guarantee the accuracy of the autofocusing results, the noise of the hologram, the intrinsic twin image in the amplitude and phase results and the wrapped ambiguity in the phase distribution are suppressed or lessened by using the four techniques stated above. The focused amplitude and unwrapped phase distributions of the sample are reconstructed, and experimental verification confirms that the present hybrid autofocusing method is a feasible, effective and promising technology with broad application prospects. [ABSTRACT FROM AUTHOR]

In an image sensor-based visible-light communication, noise reduction is essential for improving the transmission performance because each frame contains received data with various types of noises. In this study, we demonstrate the structures of receive (Rx) and transmit (Tx) frames for optical camera communication (OCC) by using the rolling shutter effect of a complementary metal-oxide semiconductor (CMOS) image sensor. We propose and demonstrate a three-step noise-reduction process for each frame. The additive white Gaussian noise is reduced by using “signal averaging,” and the background noise is reduced via “adaptive window thresholding” with “normalization.” By using the proposed method, this system shows noise tolerance. We experimentally demonstrate an 8.55-kBd error-free optical camera transmission. [ABSTRACT FROM AUTHOR]

Multipath effect in communication system is important to the quality of signals. The influence of the multipath effect on the performance of ghost imaging is investigated numerically and experimentally. The reflected light from ground glass is used as the light source to trigger the multipath effect, and we compare it with the traditional ghost imaging using transmitted light from ground glass as the light source. To compare the influence of the multipath effect, ghost imaging using reflected light from the aluminized ground glass under different distances is presented. The multipath effect is affected by the complexity of mutual interference, and it has both constructive and destructive influence on the quality of ghost imaging. The strong multipath effect increases the resolution, but it also reduces the signal-to-noise ratio of the reconstructed images. [ABSTRACT FROM AUTHOR]

Phase retrieval using single farfield image data is the key to many applications. However, this method easily falls into stagnation because of the multiple solutions. A wavefront reconstruction algorithm based on the hybrid focal lengths Fresnel zone plane is proposed in this paper. By using the proposed method the partially focused and defocused information of wavefront can be captured on just one farfield image. This method can effectively solve the phase ambiguity, and the optical structure is very simple and easy to implement. Simulation results show that the proposed method can reconstruct wavefront aberration very precisely with just one far field. [ABSTRACT FROM AUTHOR]

Based on the theory of compressive sensing, a parallel complementary compressive sensing imaging system is proposed, and the mathematical model of block parallel processing is established. Parametric analysis shows that the quality of the restored image increases with the increase of observed compression ratio and the decrease of the number of blocks, which is in conflict with total amount of data and time-consuming of algorithm, and needs to be considered comprehensively. According to the demand of space remote sensing system applied in push-broom mode, the image motion model of the system is established. The results show that the image motion has a severe effect on the quality of restored image, and increasingly responsive with the decrease of the number of blocks. when the orbital image motion parameter is constant, improving the frame rate of the detector and increasing the pixel size can obtain a smaller image motion ratio, thereby enhancing the image quality. But the application scope of the system for push-broom imaging is somewhat limited for its significantly degrade under low image motion ratio. [ABSTRACT FROM AUTHOR]

A floating aerial three-dimensional (3D) display based on the freeform-mirror and the improved integral imaging system is demonstrated. In the traditional integral imaging (II), the distortion originating from lens aberration warps elemental images and degrades the visual effect severely. To correct the distortion of the observed pixels and to improve the image quality, a directional diffuser screen (DDS) is introduced. However, the improved integral imaging system can hardly present realistic images with the large off-screen depth, which limits floating aerial visual experience. To display the 3D image in the free space, the off-axis reflection system with the freeform-mirror is designed. By combining the improved II and the designed freeform optical element, the floating aerial 3D image is presented. [ABSTRACT FROM AUTHOR]

We report on the design and implementation of an integrated dual-color stimulated emission depletion (STED) microscopy and fluorescence emission difference (FED) microscopy. This highly integrated system combines the respective advantages of STED and FED microscopies, enabling acquisition of super-resolution STED images with specific fluorophores and high laser power, or resolution-enhanced FED imaging for ordinary fluorescent dyes and other materials with moderate demand for laser power. The functional integration enables researchers to select the more appropriate microscopy according to practical scenario and requirements, giving full play to their respective strengths and satisfying the imaging demands maximally. The system’s resolution is characterized by dual-color imaging of fluorescent particles. Its practical applicability is verified through imaging various kinds of samples, including several fixed cells stained with different organic dyes and a given organic material—organometallic halide perovskite. [ABSTRACT FROM AUTHOR]

We propose a novel security scheme that uses vector beam characterized by the spatially variant polarization distribution. A vector beam is so generated that its helical components carry tailored phases corresponding to the image/images that is/are to be encrypted. The tailoring of phase has been done by employing the modified Gerchberg–Saxton algorithm for phase retrieval. Stokes parameters for the final vector beam is evaluated and is used to construct the ciphertext and one of the keys. The advantage of the proposed scheme is that it generates real ciphertext and keys which are easier to transmit and store than complex quantities. Moreover, the known plaintext attack is not applicable to this system. As a proof-of-concept, simulation results have been presented for securing single and double gray-scale images. [ABSTRACT FROM AUTHOR]

A focused plenoptic camera can effectively transform angular and spatial information to yield a refocused rendered image with high resolution. However, choosing a proper patch size poses a significant problem for the image-rendering algorithm. By using a spatial frequency response measurement, a method to obtain a suitable patch size is presented. By evaluating the spatial frequency response curves, the optimized patch size can be obtained quickly and easily. Moreover, the range of depth over which images can be rendered without artifacts can be estimated. Experiments show that the results of the image rendered based on frequency response measurement are in accordance with the theoretical calculation, which indicates that this is an effective way to determine the patch size. This study may provide support to light-field image rendering. [ABSTRACT FROM AUTHOR]

We show a method of intensity correlation imaging of targets illuminated by a sunlight-like source both theoretically and experimentally. With a Faraday anomalous dispersion optical filter (FADOF), we have modulated the coherence time of a thermal source up to 0.167 ns. And we carried out measurements of temporal and spatial correlations, respectively, with an intensity interferometer setup. By skillfully using the even Fourier fitting on the very sparse sampling data, the images of targets are successfully reconstructed from the low signal-noise-ratio(SNR) interference pattern by applying an iterative phase retrieval algorithm. The resulting imaging quality is as well as the one obtained by the theoretical fitting. The realization of such a case will bring this technique closer to geostationary satellite imaging illuminated by sunlight. [ABSTRACT FROM AUTHOR]

Color detection from a light emitting diode (LED) array using a smartphone camera is very difficult in a visual multiple-input multiple-output (visual-MIMO) system. In this paper, we propose a method to determine the LED color using a smartphone camera by applying regression analysis. We employ a multivariate regression model to identify the LED color. After taking a picture of an LED array, we select the LED array region, and detect the LED using an image processing algorithm. We then apply the k-means clustering algorithm to determine the number of potential colors for feature extraction of each LED. Finally, we apply the multivariate regression model to predict the color of the transmitted LEDs. In this paper, we show our results for three types of environmental light condition: room environmental light, low environmental light (560 lux), and strong environmental light (2450 lux). We compare the results of our proposed algorithm from the analysis of training and test R-Square (%) values, percentage of closeness of transmitted and predicted colors, and we also mention about the number of distorted test data points from the analysis of distortion bar graph in CIE1931 color space. [ABSTRACT FROM AUTHOR]

Single-pixel imaging has emerged over recent years as a novel imaging technique, which has significant application prospects. In this paper, we propose and experimentally demonstrate a scheme that can achieve single-pixel non-imaging object recognition by acquiring the Fourier spectrum. In an experiment, a four-step phase-shifting sinusoid illumination light is used to irradiate the object image, the value of the light intensity is measured with a single-pixel detection unit, and the Fourier coefficients of the object image are obtained by a differential measurement. The Fourier coefficients are first cast into binary numbers to obtain the hash value. We propose a new method of perceptual hashing algorithm, which is combined with a discrete Fourier transform to calculate the hash value. The hash distance is obtained by calculating the difference of the hash value between the object image and the contrast images. By setting an appropriate threshold, the object image can be quickly and accurately recognized. The proposed scheme realizes single-pixel non-imaging perceptual hashing object recognition by using fewer measurements. Our result might open a new path for realizing object recognition with non-imaging. [ABSTRACT FROM AUTHOR]

We propose a method of topological charge number multiplexing based on the JTC encryption system to achieve multiple-image encryption. Using this method, multi-image can be encrypted into single ciphertext, and the original images can be recovered according to the authority level. The number of encrypted images is increased, moreover, the quality of decrypted images is improved. Results of computer simulation and initial experiment identify the validity of our proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we propose a method to improve the contrast of image by using both radially symmetrical conjugating phase masks. The method is based on the generation of synthetic optical transfer function (OTF) from OTFs of both radially symmetrical conjugating phase masks. Both quartic phase mask (QPM) and its conjugating phase mask (cQPM) are used as an example. Two images are captured by QPM and cQPM. In Fourier domain, a combination of both QPM and cQPM produces the improvement of the contrast of images in all spatial frequency positions. The simulation results demonstrated that the contrast improvement of image of proposed method is obtained. [ABSTRACT FROM AUTHOR]

We theoretically study the influence of degree of polarization (DOP) of thermal light on the contrast-to-noise ratio (CNR) of the reflective ghost imaging (RGI), which is a novel and indirect imaging modality. An expression for the CNR of RGI with partially polarized thermal light is carefully derived, which suggests a weak dependence of CNR on the DOP, especially when the ratio of the object size to the speckle size of thermal light has a large value. Different from conventional imaging approaches, our work reveals that RGI is much more robust against the DOP of the light source, which thereby has advantages in practical applications, such as remote sensing. [ABSTRACT FROM AUTHOR]

A novel symmetric and asymmetric hybrid optical cryptosystem is proposed based on compressive sensing combined with computer generated holography. In this method there are six encryption keys, among which two decryption phase masks are different from the two random phase masks used in the encryption process. Therefore, the encryption system has the feature of both symmetric and asymmetric cryptography. On the other hand, because computer generated holography can flexibly digitalize the encrypted information and compressive sensing can significantly reduce data volume, what is more, the final encryption image is real function by phase truncation, the method favors the storage and transmission of the encryption data. The experimental results demonstrate that the proposed encryption scheme boosts the security and has high robustness against noise and occlusion attacks. [ABSTRACT FROM AUTHOR]

To realize volume moiré tomography (VMT) for the real three-dimensional (3D) diagnosis of combustion fields, according to 3D filtered back projection (FBP) reconstruction algorithm, the radial derivatives of the projected phase should be measured firstly. In this paper, a simple spatial phase-shifting moiré deflectometry with double cross gratings is presented to measure the radial first-order derivative of the projected phase. Based on scalar diffraction theory, the explicit analytical intensity distributions of moiré patterns on different diffracted orders are derived, and the spatial shifting characteristics are analyzed. The results indicate that the first-order derivatives of the projected phase in two mutually perpendicular directions are involved in moiré patterns, which can be combined to compute the radial first-order derivative. And multiple spatial phase-shifted moiré patterns can be simultaneously obtained; the phase-shifted values are determined by the parameters of the system. A four-step phase-shifting algorithm is proposed for phase extraction, and its accuracy is proved by numerical simulations. Finally, the moiré deflectometry is used to measure the radial first-order derivative of projected phase of a propane flame with plane incident wave, and the 3D temperature distribution is reconstructed. [ABSTRACT FROM AUTHOR]

Based on the Yamada model and rate equation model of vertical cavity surface emitting laser (VCSEL) with a saturable absorber (SA), we numerically simulate the spiking response of VCSEL–based optical spiking neuron under incoherent and coherent perturbations, respectively. First, we simply analyze the dynamics of the laser system based on the Yamada model. Then we discuss the dependence of spiking characteristics, including threshold, response time, response spike’s amplitude and pulse-width, with the amplitude of perturbations, the driving current of gain and SA region for single optical pulse injection. Finally, we study the dependence of relative refractory period of VCSEL-based optical spiking neuron with different amplitudes of perturbations. Since VCSELs are ease of integration, it provides new opportunities for realization of large-scale and ultrafast neuromorphic computing systems. [ABSTRACT FROM AUTHOR]