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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]

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 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]

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]

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]

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]

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]

Target-coordinate transformation in the lidar spot of the down-looking synthetic-aperture imaging lidar (SAIL) was performed, and the attitude errors were deduced in the process of imaging, according to the principle of the airborne down-looking SAIL. The influence of the attitude errors on the imaging quality was analyzed theoretically. A compensation method for the attitude errors was proposed and theoretically verified. An airborne down-looking SAIL experiment was performed and yielded the same results. A point-by-point error-compensation method for solving the azimuthal-direction space-dependent attitude errors was also proposed. [ABSTRACT FROM AUTHOR]

Since optical distortion has been a big trouble for various kinds of imaging systems, finding a simple correction method with wide applications is of significant importance. In this paper, we propose a unified and simple correction method, performing well for both photographic and projective imaging systems. The basic idea is regarding the optical distortion as geometrical deformation between the object and image, without considering the specific features of an optical system. First of all, a calibration template is employed to establish the geometrical transformation model (GTM) for the distortion of a built optical system. Two alternative algorithms are given to estimate the GTM in algebraic form. The computation is very simple because no intrinsic parameters of the optical system are needed to establish the GTM. Besides, the errors introduced by the fabricating and assembling process can be eliminated. Then, the corrected image of the photographic system or the pre-distorted image of the projective systems can be obtained accordingly utilizing the GTM. Experiments are conducted to demonstrate the effectiveness of our method with wide applications. [ABSTRACT FROM AUTHOR]

Lensless ghost imaging with fully spatially incoherent source is investigated theoretically and experimentally. The effects of positive and negative defocusing on lensless ghost imaging are studied by using classical optical theory and a fully spatially incoherent source. Based on the numerical calculation and experimental results, we find that the negative defocusing has a stronger influence on imaging resolution when compared with that from the positive defocusing. To explain this phenomenon, the analytical expression of point spread function with the positive and negative defocusing is presented. [ABSTRACT FROM AUTHOR]

The intensity correlation imaging method is a novel kind of interference imaging and it has favorable prospects in deep space recognition. However, restricted by the low detecting signal-to-noise ratio (SNR), it's usually very difficult to obtain high-quality image of deep space object like high-Earth-orbit (HEO) satellite with existing phase retrieval methods. In this paper, based on the priori intensity statistical distribution model of the object and characteristics of measurement noise distribution, an improved method of Prior Information Optimization (PIO) is proposed to reduce the ambiguous images and accelerate the phase retrieval procedure thus realizing fine image reconstruction. As the simulations and experiments show, compared to previous methods, our method could acquire higher-resolution images with less error in low SNR condition. [ABSTRACT FROM AUTHOR]

Pixel-by-pixel processed fluorescence difference microscopy is experimentally demonstrated by multiplexing excitation laser beams with Gaussian and donut spot shapes and then demultiplexing the fluorescent signals using lock-in amplifiers. With this scheme, a fixed sample of fluorescent spheres and a slice of mouse brain tissue are imaged with resolutions that exceed the diffraction limit. Compared to previously reported subtraction imaging techniques, this pixel-by-pixel scan can be applied to improve the resolution of a moving sample without introducing subtraction errors. The synchronized signal detection feature makes this method extendible to various applications. [ABSTRACT FROM AUTHOR]

In conventional imaging systems, the resolution of the final image is mainly distorted due to diffraction of higher spatial frequencies of the target object. To overcome the diffraction limit, imaging techniques which synthetically enlarge the aperture of the system are used. In this paper, synthesized aperture is produced by means of a three fiber illumination assembly coupled with an in-plane object rotation. The high order diffracted spatial frequencies of the object are brought into the pass band of optical system by illuminating the object with tilted beams. The tilt produced at the fiber assembly plane is related to the dimension of the aperture, placed at the Fourier plane of the system. To span the 2D object spectrum at the Fourier plane, an in-plane object rotation procedure is applied at the object plane. The spectrum of the object is rotated as the object is rotated and illuminated with tilted beams. The corresponding object beam is interfered with a reference beam from the same source to record interferograms. All the recorded interferograms are stored in computer and de-convolution algorithm is applied to recover the synthesized spectrum. The image of the synthesized spectrum has three times improved resolution compared to the conventional image. [ABSTRACT FROM AUTHOR]

In this paper, we present a color image encoding algorithm by combined use of the high-quality elemental image array (EIA) and the pseudo-random mask. To overcome low resolution drawbacks in widely used optical pickup system, in our scheme, the pseudo-inverse filter is introduced to improve this problem. In the cryptosystem, the proposed scheme provides high security because of the high key space of cellular automata. Meanwhile, the hologram-like attribute of the EIA can significantly improve the robustness of the encrypted image against some common image processing attacks. Experiments and analysis have both demonstrated the feasibility and efficiency of the image encryption algorithm. [ABSTRACT FROM AUTHOR]

Abstract: This paper develops a game system based on head pose identification techniques to control a virtual robot walking in a virtual maze environment built with Microsoft Robotics Developer Studio. Adaboost face classifiers are used to detect a face in the image and give a rough head pose classification. Two approaches are proposed to further determine more specific head poses. The first approach adopts PCA with nose template matching method, and the second one firstly uses a nose classifier to detect the nose in a detected face region and then directly utilizes the nose’s relative position information to achieve head pose classification. A method to select the best nose area is proposed to solve the problem that multi-nose areas may be detected in one face region. Experiment results show that the two approaches have comparable time consumed, but the second approach provides more correct identification results. [Copyright &y& Elsevier]

Abstract: In this paper we briefly review experimental techniques exploiting all-optical Fourier image processing inside the 4f system in order to characterize nonlinear refractive indices. Advantages and inconveniences of imaging characterization methods are outlined and their sensitivities are compared in the context of thin films measurements (that is small nonlinear phase-shift). Comparison of imaging methods with well-known nonlinear characterization techniques such as degenerate four wave mixing, I-scan and Z-scan is also done. The influence of nonlinear absorption on sensitivity of nonlinear refraction measurements is discussed. [Copyright &y& Elsevier]

Abstract: An optical setup is proposed for the implementation of compressive sensing with coherent images. This setup specifically exploits the natural multiplicative action of speckle noise occurring with coherent light, in order to optically realize the essential step in compressive sensing which is the multiplication with known random patterns of the image to be acquired. In the test of the implementation, we specifically examine the impact of several departures, that exist in practice, from the ideal conditions of a pure multiplicative action of the speckle. In such practical realistic conditions, we assess the feasibility, performance and robustness of the optical scheme of compressive sensing. [Copyright &y& Elsevier]

Abstract: We present a novel concept for microscopic imaging. The proposed microscope-like device does not include an objective lens neither a condenser. Instead, a metallic plate of sub-wavelength hole-array with a varying pitch is used to illuminate the inspected object that is mounted very close to it. As a result, the transmitted spectrum through each hole differs from the others and therefore, each spot of the detected object is illuminated with a unique spectrum. By measuring a single spectrum that is the sum of all the spectra that are transmitted through the sample and by using spectral decomposition algorithms, the spatial transmission pattern of the object can be extracted. [Copyright &y& Elsevier]

Abstract: In this paper, we propose an enhanced computational integral imaging system by both eliminating the occlusion in the elemental images recorded from the partially occluded 3D object and recovering the entire elemental images of the 3D object. In the proposed system, we first obtain the elemental images for partially occluded object using computational integral imaging system and it is transformed to sub-images. Then we eliminate the occlusion within the sub-images by use of an occlusion removal technique. To compensate the removed part from occlusion-removed sub-images, we use a recursive application of PCA reconstruction and error compensation. Finally, we generate the entire elemental images without a loss from the newly reconstructed sub-images and perform the process of object recognition. To show the usefulness of the proposed system, we carry out the computational experiments for face recognition and its results are presented. Our experimental results show that the proposed system might improve the recognition performance dramatically. [Copyright &y& Elsevier]

Abstract: Multiresolution analysis is very useful for characterization of textures, segmentation tasks, and feature enhancement. The development of optical methods to perform such procedures is highly promissory for real-time applications. Usually, the optical implementations of multiresolution analysis consist in the decomposition of the input scene in different frequency bands, obtaining various filtered versions of the scene. However, under certain circumstances it could be useful to provide just one version of the scene where the different filters are applied in different regions. This procedure could be specially interesting for biological and medical applications in situations when the approximate localization of the scale information is known a priori. In this paper we present a fully optical method to perform multiresolution analysis with spatial localization. By means of the proposed technique, the multi-scale analysis is performed at once in a unique image. The experimental set-up consist of a double-pass convergent optical processor. The first stage of the device allows the multiple band decomposition, while the second stage confines the information of each band to different regions of the object and recombines it to achieve the desired operation. Numerical simulations and experimental results, which prove the very good performance of the method, are presented. [Copyright &y& Elsevier]

Abstract: A wavefront reconstruction method by two-step generalized phase-shifting interferometry (GPSI) with blind phase shift extraction algorithm is verified by both the computer simulations and optical experiments. This method can retrieve complex object wave field by using two interferograms, the recorded object and reference wave intensities, and an unknown phase shift without additional processing. The simulations with irregular wavefronts have shown the effectiveness and high accuracy of this method for blind phase-shift extraction and wavefront reconstruction over a wide range of phase-shifts, while the optical experiments for both the direct and indirect objects have yielded satisfactory results with a higher resolution of reconstructed image than those reported recently. [Copyright &y& Elsevier]

Fourier ptychographic microscopy has recently attracted attention because of its ability to expand the space–bandwidth products of an imaging system. To improve the efficiency of information acquisition, large numerical apertures and low-overlapping rates should be employed. However, the pixel aliasing problem occurs in phase recovery in the under-sampling condition. An algorithm was developed to solve the pixel aliasing problem with low overlapping requirements. Combined with total variational optimization procedures, the overlapping requirements were reduced, and the noise was suppressed. Compared with the upsampled method, the proposed algorithm achieved evident overlapping rate reduction. With a spatial-sampling ratio of 0.72, satisfactory effects were achieved at the minimum overlapping rate of 24% in simulation, which meant a significant reduction in the amount of data. A limitation for the objective lens aperture was identified, and a theoretical explanation is proposed. • An algorithm to solve the pixel aliasing problem with low overlapping requirements for FPM. • Overlapping requirements were reduced, and the noise was suppressed. • Excellent results with spatial-sampling ratio of 0.72 and overlapping rate of 24%. [ABSTRACT FROM AUTHOR]

Abstract: A novel digital image watermarking system based on an iterative phase retrieval algorithm and sine–cosine modulation in the discrete-cosine-transform (DCT) domain is proposed. The original hidden image is first encrypted into two phase masks. Then the cosine and sine functions of one of the phase masks are introduced as a watermark to be embedded into an enlarged host image in the DCT domain. By extracting the watermark of the enlarged superposed image and decryption we can retrieve the hidden image. The feasibility of this method and its robustness against some attacks, such as occlusion, noise attacks, quantization have been verified by computer simulations. This approach can avoid the cross-talk noise due to direct information superposition and enhance the imperceptibility of hidden data. [Copyright &y& Elsevier]

Abstract: The tendency today is to replace high-dynamic light modulators by high-speed binary ones (of which the micromirror is the best example). This kind of spatial light modulators (SLM) fulfils all the present needs in displays. They are used in optical communications as binary systems and also in display applications (video projectors) with temporal multiplexing, in order to generate greyscale or colour images. In optical processing, and in the majority of coherent applications, temporal dithering introduces some distortions. In this paper, this point is studied with simulations. We point out that temporal multiplexing cannot be used in the Fourier plane. In the imaging plane, the distortion is weak if the filter has a positive impulse response. [Copyright &y& Elsevier]

Abstract: A method for omnidirectional real-time optical edge extraction is proposed. The method consists on the design of a complex filter that is implemented in a Vander Lugt like optical processor. It is emphasized the rotation invariance of the technique, as its equivalence with the Canny edge detector. Numerical simulations have been performed to compare the proposed implementation with some frequently used edge detectors and enhancers. Experimental results are presented to show the very good performance of the method. [Copyright &y& Elsevier]

Abstract: We present an improved method of speckle-illuminated non-scanning fluorescence confocal microscopy that uses an optically addressed spatial light modulator (OASLM) to perform real-time image processing. Results are presented from an experimental system in which a miniature LCD in combination with an analogue CCD camera operates as the OASLM. The ability of this method to produce processed images possessing confocal characteristics and to remove additive detector noise is demonstrated with both computer simulation and experimental results. [Copyright &y& Elsevier]

Abstract: We present a high-resolution spectral domain optical coherence tomography (SDOCT) device with a broad-band supercontinuum light generated in a photonic crystal fiber. The instrument we have developed has an axial resolution of 4 μm in air, a depth of image of 1 mm, and an exposure time of 128 μs per a single A-scan. We adopt and apply two methods for data analysis, which reduce the effects of a strong modulation and temporal fluctuations exhibited by the spectra of supercontinuum. To demonstrate the potential of the methods we show high-resolution SDOCT cross sectional images of the human cornea and retina in vivo. [Copyright &y& Elsevier]

Abstract: We describe a full-field optical coherence tomography (OCT) system for extracting 2D cross-sectional images from a multiple-layer information carrier. A simple and practical method is used to remove the fringes in the extracted cross-sectional interference images. To the best of our knowledge, for the first time, the inter-layer-modulation effect of 2D OCT is proposed and analyzed. The related algorithms for de-modulation and image enhancement are formulated. This system has the potential to be used for document security and object identification. [Copyright &y& Elsevier]

Demonstrated for a digital image sensor-based camera is a calibration target optimized method for finding the Camera Response Function (CRF). The proposed method uses localized known target zone pixel outputs spatial averaging and histogram analysis for saturated pixel detection. Using the proposed CRF generation method with a 87 dB High Dynamic Range (HDR) silicon CMOS image sensor camera viewing a 90 dB HDR calibration target, experimentally produced is a non-linear CRF with a limited 40 dB linear CRF zone. Next, a 78 dB test target is deployed to test the camera with this measured CRF and its restricted 40 dB zone. By engaging the proposed minimal exposures, weighting free, multi-exposure imaging method with 2 images, demonstrated is a highly robust recovery of the test target. In addition, the 78 dB test target recovery with 16 individual DR value patches stays robust over a factor of 20 change in test target illumination lighting. In comparison, a non-robust test target image recovery is produced by 5 leading prior-art multi-exposure HDR recovery algorithms using 16 images having 16 different exposure times, with each consecutive image having a sensor dwell time increasing by a factor of 2. Further validation of the proposed HDR image recovery method is provided using two additional experiments, the first using a 78 dB calibrated target combined with a natural indoor scene to form a hybrid design target and a second experiment using an uncalibrated indoor natural scene. The proposed technique applies to all digital image sensor-based cameras having exposure time and illumination controls. In addition, the proposed methods apply to various sensor technologies, spectral bands, and imaging applications. [ABSTRACT FROM AUTHOR]

A new real-time, high-precision three-dimensional (3D) laser radar with a coherent system is presented. A self-designed arbitrary waveform generator (AWG), an electro-optic modulator, and an optical filter are proposed to generation a linear frequency modulated continuous waveform (FMCW) with a bandwidth of 2.4 GHz and pulse repetition frequency (PRF) of 100kHz. The heterodyne coherent detection and Micro-Electro-Mechanical System (MEMS) scanner are implemented with high sensitivity and fast 3D imaging. At the same time, multi-phase FFT algorithm is proposed to realize the frequency calculation with real-time. In this paper, we present the system structure, signal processing, and the experimental results in detail. The system achieves static 3D target and dynamic target imaging verification, and the experiment result validates the performance of system for real-time 3D imaging. It acquires 3D imaging at 40 frames per second (fps), which can satisfy the demand of high imaging speed requirements for special situation. • A new real-time, high-precision three-dimensional (3D) laser radar with a coherent system is presented. • Multi-phase FFT algorithm is proposed to realize the frequency calculation with real-time. • The experiment result validates the performance of system for realtime 3D imaging. • The system acquires 3D imaging at 40 frames per second (fps), which can satisfy the demand of high imaging speed requirements for special situation. [ABSTRACT FROM AUTHOR]

A novel noise model is proposed for a balanced-detection ultrafast imaging system to comprehensively analyze the noise in the system. The whole noise model is obtained by solving for erbium-doped fiber amplifier (EDFA) noise, intersymbol interference (ISI) noise and low-pass filter (LPF) noise successively with stochastic process theory. Then, the nonmonotonic relationship between the cut-off frequency and the signal-to-noise ratio (SNR) for certain experimental parameters are derived quantitatively and qualitatively: the SNR first increases and then decreases when the cut-off frequency increases, while the unique extreme point is located at 6.3 GHz. In addition, imaging results are obtained accordingly. The model and the results can provide a reference for system design and parameter selection. [ABSTRACT FROM AUTHOR]

It has always been a hot topic to break the angular resolution/field-of-view (FOV) invariant and achieve a near-eye display with a large FOV and high-resolution. We present a super-resolution method for near-eye displays by overlapping images from two display panels using a half mirror. Key aspects including theoretical analysis, optimized method, system set-up, and calibration process are discussed detailly. A proof-of-concept prototype was developed to provide a super-resolution image capable of significantly higher sampling rate. [ABSTRACT FROM AUTHOR]