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The novel rotating synthetic aperture imaging system has the advantages of short processing cycle, light weight, low cost, and convenient transport, which is a potential development direction for future optical satellite payloads with ultra-large aperture. However, influenced by the coupling effects of the rectangular primary mirror, rotating imaging, and link perturbation, images from this system may have unique spatial and temporal variability with resolution anisotropy, resulting in the dynamics and weak features of targets. The insufficient recognition of system characteristics seriously restricts the application ability of corresponding target interpretation methods. To address this problem, we start with the analysis of system imaging characteristics and target interpretation mechanisms. Considering calculating texture, grayscale, and edge feature parameters in evaluation regions of different sizes, we propose a degradation assessment method based on multi-scale feature characterization. Then, combined with the theoretical calculation and practical target detection experiments, the influence of crucial parameters such as the aspect ratio and rotation angle of the primary mirror on the target interpretation capability is analyzed. The results will provide guidance for the integrated design and optimization of optical imaging systems and intelligent image processing methods. • A degradation assessment method based on multi-scale feature characterization is proposed. • The effect of rotating synthetic aperture system on image target characteristic degradation is analyzed. • The impacts of key system parameters on target detection performance are analyzed. [ABSTRACT FROM AUTHOR]

• Holographic images can be combined coherently to increase image resolution and field of view. • The choice of illumination and observation geometries affect the point-spread and transfer characteristics of the imaging system. • Phase contrast imaging in transmission and reflection geometries is possible. This paper discusses a modular implementation of synthetic aperture interferometry (SAI) using inexpensive telecommunications technologies that can be expanded for use in optical instruments with arbitrarily large fields of view. Exploiting multiple image sensors and multiple illumination sources, transmission and reflection SAI geometries, capable of emulating the phase contrast and interference modes of conventional interference microscopes, are considered. The point-spread and transfer characteristics of these geometries are illustrated for the case of a transmission mode instrument. It is shown that although imaging is strictly field dependent (i.e. shift-variant), the response of modular instruments is periodic and with careful choice of illumination and sensor positioning can be made quasi shift-invariant. We demonstrate SAI in a transmission configuration comprising of a single coherent imager that holographically records the field scattered from a test target sequentially illuminated by 16 different plane waves. This set-up is equivalent to a single module of a larger SAI system and since brightfield regions in the individual reconstructed images overlap, provides an ideal platform to examine the effect of tilt and phase offset errors in the illumination. By applying a first order correction and assuming phase continuity over the overlapping regions, we demonstrate a significant improvement in the SAI reconstruction. [ABSTRACT FROM AUTHOR]

• An ultra-compact add-on module (about 30 mm in total) based on two polarization gratings is built for single shot DIC type quantitative phase imaging. • A fast sythethis aperture (line-scanning) method is proposed. • The zdirectional sectional ability of 3D phase imaging is discuused in the supplementary material and several important conlusions are made. Differential interference contrast (DIC) microscopy is an important member of quantitative phase imaging (QPI) family owing to its simple optical implementation and high compatibility regarding to different coherence degree of illumination field. Such compactivity means that the DIC-based phase imaging can be conveniently converted between 2D-integrational and 3D-sectional modes by switching the spatial coherence degree of illumination field between low degree and high. However, there is a potential trade-off compromise in the existed experimental implementations for DIC imaging regarding to the optical simplicity, space-bandwidth utilization and temporal resolution. In this manuscript, we proposed a polarization gratings pair (PGs) based off-axis DIC system to realize integrational and sectional QPI. Building on a bright field microscope and getting rid of the additional 4f lens system, the proposed PGs-DIC system can realize single-shot QPI with an ultra-compact optical configuration. In order to improve the imaging resolution and optical sectional ability, a fast synthetic aperture technology is introduced, in which multiple interferograms with different line-filtered illumination are captured. Both high resolution 2D-integrational and 3D-sectional phase imaging results indicate that the proposed PGs-DIC system is a good candidate for QPI. Specially, a theoretical model is proposed to quantitatively estimate z-direction resolution for z -scanning 3D phase imaging technology and future application in the PGs-DIC system. [ABSTRACT FROM AUTHOR]

• The current Fourier ptychographic imaging need high aperture overlapping ratio to ensure the convergence. This limitation dictates that the images can only be acquired by dense aperture scanning. We proposed a new framework to solve the Fourier ptychographic imaging with sparse aperture. Our method breaks the limitation of dense aperture scanning and allows multiple separate imaging systems to capture images simultaneously, which could simplify the imaging configuration and improve the acquisition efficiency. • In our work, the aperture overlapping ratio is reduced to less than 25% for the first time. The imaging quality of proposed method also outperforms than the state-of-the-art methods under the same imaging parameters. Our work shows the potential for single-shot imaging by using a camera array instead of aperture scanning mentioned in previously published works, so that the observation of rapidly changing scenes can be realized. Synthetic aperture technique could effectively expand the passband and beyond the diffraction limit of aperture. Macroscopic Fourier ptychography (FP) makes synthetic aperture feasible in visible light by incorporating phase retrieval process into synthetic aperture. In FP, a dense aperture sampling is necessary to overcome the ill-posedness of phase retrieval, which leads to long acquisition time and heavy computation. Here, a total variation regularization-based Fourier ptychographic (TVFP) reconstruction method is proposed for long-range imaging. The TVFP method imposes total variation constraints to improve the ill-posedness of the imaging model, and recovers high-quality image from sparse aperture sampling. For the imaging system with aberration, a joint optimization of pupil function and target image is also proposed to achieve the aberration free image and the estimated pupil function simultaneously. The results show the aperture overlapping ratio could be reduced to 25% or less. The proposed method simplifies the imaging configuration and improves the robustness for long-range imaging. [Display omitted] [ABSTRACT FROM AUTHOR]

The blur is a problem impacting the image quality of optical synthetic aperture imaging (OSAI) system and requiring image restoration techniques for deconvolution. However, most traditional image deconvolution algorithms are non-blind methods and also highly susceptible to the unknown noise. The turbulence perturbation and the co-phase error are both factors that may affect the recovery performance. As for the image restoration under noises and turbulence correction error, a further optimized network named as RestoreNet-Plus is designed. After further optimization, RestoreNet-Plus has advantages as below: • Blind restoration ability and generalization capacity: RestoreNet-Plus could remove the blur better in the blind way facing different targets through OSAI system; • Anti-noise ability: It could beat other methods under different levels noises, including Wiener filter, Hyper-Laplacian prior algorithm, Lucy-Richardson algorithm, Blind Deconvolution algorithm and RestoreNet. • Anti-turbulence correction error ability: RestoreNet-Plus could maintain good Blind restoration ability under the influence of turbulence correction error in imaging. • Fast for applying: RestoreNet-Plus performances the best in the image restoration of OSAI system under noises and turbulence correction error with only 54 ms time costs. The synthetic aperture technology can improve the resolution effectively in the optical imaging system. In fact, the imaging blur, turbulence aberration and noise can affect the imaging quality of optical synthetic aperture imaging system seriously. Several non-blind methods are applied generally to recover the degraded maps with the prior information. However, the restoration effect is not stable enough and satisfactory. As a data-driven approach, the deep learning framework possesses advantages in solving this problem. In this paper we propose an improved network, RestoreNet-Plus, for the image restoration of optical synthetic aperture imaging system. After the proofs of numerical simulation and experiment results, RestoreNet-Plus is a better alternative compared with other methods, owing to its better restoration ability, strong denoising ability and capacity for turbulence correction error. [ABSTRACT FROM AUTHOR]

• The imaging mechanism of the novel rotating synthetic aperture system is deduced. • The image degradation model of the rotating synthetic aperture system is presented. • The effects of factors causing image quality degradation are analyzed. The Rotating synthetic aperture (RSA) is one of the most promising novel imaging systems to meet the requirements of lightweight and high resolution for optical remote sensing satellites, especially in geostationary orbit. The point spread function (PSF) orientation relative to the observed scene, intentionally changes to measure all spatial frequency information available to a filled circular aperture having a diameter approximately equal to the length of the rectangular aperture. As with all precision optical systems, RSA is also subject to dynamic disturbances from the spacecraft/environment. If not accommodated properly in the measurement and synthesis process, the dynamic disturbances can result in significant image quality degradation. To quantify methods to reduce or eliminate the errors, we first analyze the on-orbit imaging mechanism of the RSA system theoretically and then represent the worst-case on-orbit imaging degradation characteristics. [ABSTRACT FROM AUTHOR]

• A diffusing model and an aliasing-free DOF model were proposed to analyses the influence of the position and diffusing-angle for holographic diffuser based InIm display system. • The larger the diffusing-angle and the farther away from the reconstructed point, the more blurred the reconstructed image will be. • Enhanced aliasing-free depth of field and better viewing effect are achieved, when the holographic diffuser is located at the far-end of the marginal depth plane instead of the traditional central depth plane. The holographic diffuser plays a significant role in the reconstruction performance of the large-size integral imaging display system. However, the influence of the holographic diffuser on the display quality is seldom theoretically analyzed. In this paper, a quantitative beam analysis approach is proposed, and a diffusing model is established to analyses the influence of the position and diffusing-angle of the holographic diffuser on different reconstruction points, then the mechanism of the aliasing effect caused by the holographic diffuser is revealed. Both the numerical and optical experiments are implemented to prove the validity of the established model, and the results are well agreed with the theoretical analysis, which shows that when the holographic diffuser with a certain diffusing-angle is located at the far-end of the marginal depth plane instead of the traditional central depth plane (CDP), the system can obtain an enhanced aliasing-free depth of field and have a better viewing effect, which is inconsistent with the traditional intuition and experience. [ABSTRACT FROM AUTHOR]

• Non-blind algorithms, such as the Wiener filter and the Lucy-Richardson algorithm, are always used to restore images of the optical synthetic aperture imaging (OSAI) system, but can't apply in practice easily due to the unknown prior information of system. Deep learning is a new technology rising nowadays, and has many successful application cases in different fields. An improved U-shaped network named RestoreNet is designed to remove the blur and recover the image from OSAI system. • After enough training, RestoreNet has advantages as below: • Restoring ability : After enough training, RestoreNet can remove the blur definitely and easily in OSAI system; • Fast for applying : In testing period, the recovering time for one image is just ~30ms , but the restoration effect is better than the Lucy-Richardson algorithm, which takes 470ms for one image; • Prior information unknown : RestoreNet can restore images without the prior information of system , for example, the point spread function or the optical transfer function, which is not provided by the non-blind algorithms; • Generalization ability : RestoreNet has strong ability in generalization ability whether facing different types of images or imaging systems with different sub-aperture arrangements. Imaging blur is an inevitable problem in optical synthetic aperture imaging system because of the low response of frequency. Non-blind deconvolution algorithms are usually used for image restoration to obtain clear and high-resolution images. However, accurate prior information on the optical transfer function of system is required in the non-blind methods. As a data-driven approach, recent developments in deep learning have shown great potential in image processing. In this paper, a U-shaped deep learning framework named RestoreNet is proposed for image restoration, especially for removing the blur of optical synthetic aperture imaging system in a blind way. Numerical simulation and experiment results show that RestoreNet is an effective alternative with great restoration ability, stability and generalization in the image restoration of optical synthetic aperture imaging system. [ABSTRACT FROM AUTHOR]

• We present a multi-camera-based method for improving data capture speed in Fourier ptychographic microscopy. • A new reconstruction algorithm along with robust calibration methods are proposed for multi-camera Fourier ptychographic systems. • A proof-of-concept experiment is performed to validate the principle by imaging a resolution target and a plant root cross section, using 9 times fewer LED illuminations compared to a regular Fourier ptychographic setup. We present a novel microscopy concept, termed Multi-Aperture Fourier ptychographic microscopy (MA-FPM), to enable implementation of parallel detectors in microscopy to increase the space-bandwidth-time product. MA-FPM is a synthetic aperture technique: an array of objectives together with tilt-shift illumination are used to synthesize high-resolution, wide field-of-view images. Here, the phase is recovered using Fourier ptychography (FP) algorithms unlike conventional optical synthetic aperture techniques where holographic measurements are used. In this article we report a proof-of-concept experiment by translating a lens and a detector to positions according to the proposed design and demonstrate high-quality imaging performance despite using nine-fold fewer illumination angles compared to an equivalent FP setup. Calibration procedures and a reconstruction algorithm were developed to address the challenges of multiple imaging systems. [ABSTRACT FROM AUTHOR]