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Nowadays, new technologies such as Internet of Things (IoT) applications depend on biometrics for authentication and identity verification. These biometrics contain confidential information about the user. It is necessary to keep these biometrics in a secure template. The Cancelable Biometric System (CBS) aims to protect biometric traits by preserving them in an intended distorted template. This paper presents a cancelable multimodal biometric authentication system based on optical encryption algorithms and watermarking. The new trend in biometric authentication systems is to use Electroencephalography (EEG) signals. The proposed CBS is based on merging the EEG signal with another biometric image, then the obtained data is encrypted by optical encryption software. Double Random Phase Encoding (DRPE), Optical Scanning Holography (OSH), cascade DRPE-OSH, and cascade OSH-DRPE are applied separately to encrypt the merged data and get the final cancelable template. Simulation results prove the high accuracy and efficiency of the proposed system, as the Equal Error Rate (EER) value is close to 0 and the Area under the Receiver Operator Characteristic (AROC) is close to 1. Simulation results indicate the performance stability of the proposed system in the presence of different types of noise and attacks. [ABSTRACT FROM AUTHOR]

Holographic techniques are indispensable tools for modern optical engineering. Over the past two decades, research about incoherent digital holography has continued to attract attention. Optical scanning holography (OSH) can obtain incoherent holograms using single-pixel detection and structured illumination with Fresnel zone patterns (FZPs). Particularly by changing the size of a detector, OSH can also obtain holograms under coherently illuminated conditions. Since 1979, OSH has continuously evolved. According to the evolution of semiconductor technology, spatial light modulators (SLMs) come to be useful for various imaging fields. By using SLM techniques for OSH, the practicality of OSH is improved. These SLM-based OSH methods are termed computational OSH (COSH). In this review, the configurations, recording and reconstruction methods, and proposed applications of COSH are reviewed. [ABSTRACT FROM AUTHOR]

Holographic techniques are indispensable tools for modern optical engineering. Over the past two decades, research about incoherent digital holography has continued to attract attention. Optical scanning holography (OSH) can obtain incoherent holograms using single-pixel detection and structured illumination with Fresnel zone patterns (FZPs). Particularly by changing the size of a detector, OSH can also obtain holograms under coherently illuminated conditions. Since 1979, OSH has continuously evolved. According to the evolution of semiconductor technology, spatial light modulators (SLMs) come to be useful for various imaging fields. By using SLM techniques for OSH, the practicality of OSH is improved. These SLM-based OSH methods are termed computational OSH (COSH). In this review, the configurations, recording and reconstruction methods, and proposed applications of COSH are reviewed.

Polarization information is useful for various applications such as remote sensing and biomedical imaging. In general, polarization information is obtained using a polarization camera; however, the measured data are two-dimensional (2D) images, which limits its application. In this paper, three-dimensional (3D) polarization imaging by use of optical scanning holography (OSH) is proposed. Polarization-dependent digital holograms are recorded by changing directly the transmission axis of a polarizer in front of a photo detector. In the proof-of-principle experiment, partially Stokes parameters are calculated from the obtained holograms and are compared with the results obtained by a polarization camera. Experimental results show that the proposed method can measure a polarization object although there is the object behind a scattering medium, which opens the door of alternative imaging fields. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a physical experiment of optical scanning holography based on random-phase encoding and connected component labeling. Usually, a pinhole is used as one of pupil functions in conventional optical scanning holography experiment. Although such a structure is relatively simple, defocus noise trends to appear as a blur in sectional image reconstruction. In our experiments, a random-phase pupil is used, and it can easily transform defocus noise into speckle-like patterns with the increase in defocus distance. We apply connected component labeling to deal with the speckles, and the focus image can be recovered clearly from reconstructed images. [ABSTRACT FROM AUTHOR]

Optical scanning holography (OSH) is a powerful holographic recording technique that employs a single-pixel photo-detector and 2D scanning mechanism to capture the hologram of a wide-view and 3D object. However, in OSH experiments, we found that 2D $X$ – $Y$ scanning mirrors would cause unavoidable magnification and lateral resolution issues in 3D recording or sectioning imaging. In this letter, we will discuss this problem both theoretically and experimentally. The experiment results show that our results have a good performance on these issues. [ABSTRACT FROM AUTHOR]

Optical scanning holography (OSH) is a powerful and effective method for capturing the complex hologram of a three-dimensional (3-D) scene. Such captured complex hologram is called optical scanned hologram. However, reconstructing a focused image from an optical scanned hologram is a difficult issue, as OSH technique can be applied to acquire holograms of wide-view and complicated object scenes. Solutions developed to date are mostly computationally intensive, and in so far only reconstruction of simple object scenes have been demonstrated. In this paper we report a low complexity method for reconstructing a focused image from an optical scanned hologram that is representing a 3-D object scene. Briefly, a complex hologram is back-propagated onto regular spaced images along the axial direction, and from which a crude, blocky depth map of the object scene is computed according to non-overlapping block partitioned entropy minimization. Subsequently, the depth map is low-pass filtered to decrease the blocky distribution, and employed to reconstruct a single focused image of the object scene for extended depth of field. The method proposed here can be applied to any complex holograms such as those obtained from standard phase-shifting holography. [ABSTRACT FROM AUTHOR]

In sectional image reconstruction based on optical scanning holography (OSH) system, tomographic images are always contaminated by defocus noise. Though lots of methods have been proposed to solve this problem, some unsatisfactory results remain. In this article, a modified image fusion method is presented based on wavelet transform and connected component algorithms to deal with the defects in a random-phase OSH system where different sectional images usually have a relative displacement, rotation and loss. The method can fully utilize redundant information and affine transformation to repair the defects, and the defocus noise can be removed well. The final sectional images are more visible. [ABSTRACT FROM AUTHOR]

Digital holography (DH) is a promising technique for modern three-dimensional (3D) imaging. Coherent holography records the complex amplitude of a 3D object holographically, giving speckle noise upon reconstruction and presenting a serious drawback inherent in coherent optical systems. On the other hand, incoherent holography records the intensity distribution of the object, allowing a higher signal-to-noise ratio as compared to its coherent counterpart. Currently there are two incoherent digital holographic techniques: optical scanning holography (OSH) and Fresnel incoherent correlation holography (FINCH). In this review, we first explain the principles of OSH and FINCH. We then compare, to some extent, the differences between OSH and FINCH. Finally, some of the recent applications of the two incoherent holographic techniques are reviewed. [ABSTRACT FROM AUTHOR]

• Off-axis optical scanned holograms are recorded experimentally and reconstructed. • Without the use of heterodyning, we devised a phase-monitoring module to calibrate the phase of the recorded holograms. • Both coherent-mode and incoherent-mode off-axis OSH are demonstrated and discussed. We have built a system for off-axis optical scanning holography (OSH) and for the first time experimentally demonstrated the recording of a hologram without heterodyning or a spatial light modulator for temporal frequency shifting. To solve the problem of phase fluctuation, a phase monitoring module is included in the system. Single sideband filtering together with phase compensation is performed for the reconstruction without the zeroth-order light and the twin image. Properties and practical issues in the coherent-mode and incoherent-mode of off-axis OSH are also discussed. [ABSTRACT FROM AUTHOR]

Optical scanning holography (OSH) is a distinct digital holography technique, which uses a single two-dimensional (2D) scanning process to record the hologram of a three-dimensional (3D) object. Usually, these 2D scanning processes are in the form of mechanical scanning, and the quality of recorded hologram may be affected due to the limitation of mechanical scanning accuracy and unavoidable vibration of stepper motor’s start-stop. In this paper, we propose a new framework, which replaces the 2D mechanical scanning mirrors with a Digital Micro-mirror Device (DMD) to modulate the scanning light field, and we call it OSH based on Compressive Sensing (CS) using a digital micro-mirror device (CS-OSH). CS-OSH can reconstruct the hologram of an object through the use of compressive sensing theory, and then restore the image of object itself. Numerical simulation results confirm this new type OSH can get a reconstructed image with favorable visual quality even under the condition of a low sample rate. [ABSTRACT FROM AUTHOR]

Optical scanning holography (OSH) is a powerful and effective method for capturing the complex hologram of a three-dimensional (3-D) scene. Such captured complex hologram is called optical scanned hologram. However, reconstructing a focused image from an optical scanned hologram is a difficult issue, as OSH technique can be applied to acquire holograms of wide-view and complicated object scenes. Solutions developed to date are mostly computationally intensive, and in so far only reconstruction of simple object scenes have been demonstrated. In this paper we report a low complexity method for reconstructing a focused image from an optical scanned hologram that is representing a 3-D object scene. Briefly, a complex hologram is back-propagated onto regular spaced images along the axial direction, and from which a crude, blocky depth map of the object scene is computed according to non-overlapping block partitioned entropy minimization. Subsequently, the depth map is low-pass filtered to decrease the blocky distribution, and employed to reconstruct a single focused image of the object scene for extended depth of field. The method proposed here can be applied to any complex holograms such as those obtained from standard phase-shifting holography.

Digital holography (DH) is a promising technique for modern three-dimensional (3D) imaging. Coherent holography records the complex amplitude of a 3D object holographically, giving speckle noise upon reconstruction and presenting a serious drawback inherent in coherent optical systems. On the other hand, incoherent holography records the intensity distribution of the object, allowing a higher signal-to-noise ratio as compared to its coherent counterpart. Currently there are two incoherent digital holographic techniques: optical scanning holography (OSH) and Fresnel incoherent correlation holography (FINCH). In this review, we first explain the principles of OSH and FINCH. We then compare, to some extent, the differences between OSH and FINCH. Finally, some of the recent applications of the two incoherent holographic techniques are reviewed.

Spatial light modulators (SLMs), used for wavefront modulation in holography, present considerable limitations. Undesired contributions, e.g., zeroth diffraction order and twin images, degrade image quality, whereas higher diffraction orders limit the imaging window. We present an innovative approach for displaying complex information with two SLMs by numerically compensating for the physical misalignment of devices. This complex display enables the reduction of noise that originates from twin images, and extends the imaging window. Our alignment method is demonstrated in the case of complex modulation, though its application can be extended to other cases where precise alignment of multiple SLMs is needed. [ABSTRACT FROM PUBLISHER]

For the implementation of a real-time holographic camera, fast and automatic holographic image reconstruction is an essential technology. In this paper, we propose a new automatic depth-detection algorithm for fast holography reconstruction, which is particularly useful for optical scanning holography. The proposed algorithm is based on the inherent phase difference information in the heterodyne signals, and operates without any additional optical or electrical components. An optical scanning holography setup was created using a heterodyne frequency of 4 MHz with a 500-mm distance and 5-mm depth resolution. The reconstruction processing time was measured to be 0.76 s, showing a 62% time reduction compared to a recent study. [ABSTRACT FROM AUTHOR]

• The manuscript propose a deep-learning network for high quality image reconstruction of digital holograms recorded by optical scanning holography (OSH) system for the first time. • A two-pupil optical heterodyne scanning system is used to obtain the training data where a five-fold cross validation method is applied to prevent from overfitting and produce enough images in the dataset. • Numerical simulations and optical experiments demonstrate that our proposed method can eliminate the defocus noise and generate high quality reconstruction results significantly if correctly trained with our dataset. Optical scanning holography (OSH) can be used to record holograms of large three-dimensional (3-D) objects, based on a two-dimensional (2-D) optical scan. For semi-transparent objects, diffraction waves from all the sections can be recorded in the hologram. Numerical reconstruction of a 3-D volumetric image from an optical scanned hologram is a difficult task. The main problems are the intensive computational load, and the heavy blurring of each reconstructed section with the defocused noise from other sections. In this paper, we propose a deep-learning network for high quality image reconstruction from the optical scanned holograms. Within the framework, a U-net structure is adopted to learn the mapping between a collection of holograms, and their reconstructed volumetric images. We use a two-pupil optical heterodyne scanning system to obtain the training data where a five-fold cross validation method is used to prevent from overfitting and produce enough images in the dataset. The deep-learning based OSH can eliminate the defocus noise and generate high quality reconstruction results from an unknown hologram. Our proposed method is significantly faster than conventional OSH reconstruction algorithms, and hence suitable for processing large holograms that are captured by OSH. The feasibility of our approach is demonstrated with numerical simulations and optical experiments. The deep-learning reconstruction method proposed in the present paper is also applicable to other digital holograms obtained from conventional digital holographic systems. [ABSTRACT FROM AUTHOR]

In optical scanning holography (OSH), the object is raster scanned by a heterodyne fringe pattern. The light scattered from the object is detected by a photodetector. Traditionally, the photo-electric signal is demodulated by a dual-channel lock-in amplifier (LIA) to extract a complex hologram. The use of LIA complicates the detection module of the system and increases the cost, especially when the heterodyne frequency is high. In this paper, an alternative demodulation method called a spatial–temporal demodulation technique (STDT) is studied. In STDT, the photo-electric temporal signal is directly digitized as scanning lines. The spectrum of each scanning line is band-pass filtered to remove the zeroth-order term and the complex conjugate term. Finally, a complex hologram is obtained from the filtered spectrum. The first merit of STDT is that the phase of the demodulated complex hologram is insensitive to the modulation error. Thus it is easily applied to the applications of particle holography. Besides, the bandwidth of the zeroth-order term in STDT is narrow, which allows the system to be operated in a wide range of heterodyne frequency. This feature enables STDT-based OSH to be applied in low-cost and high-speed dynamic holographic imaging. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, by analyzing variance and noise probability distribution of the reconstructed image, a point spreading situation of adjacent section under the conventional optical scanning holography (OSH) method and a new one based on random-phase encoding (RPE) are studied. Simulation results show that, compared to the conventional OSH at the same de-focus distance, the RPE-OSH can lead the distribution of reconstructed adjacent sections to be more homogeneous and manifested as a speckle-like pattern on the in-focus image. Further study shows that the complex amplitude probability distribution of adjacent section meets the shape of Gaussian curve, and noise can be filtered out by some corresponding filters. So aliasing and interference on the in-focus image can be removed. [Copyright &y& Elsevier]

With the advancement of computers, digital holography (DH) has become an area of interest that has gained much popularity. Research findings derived from this technology enables holograms representing three dimensional (3-D) scenes to be acquired with optical means, or generated with numerical computation. In both cases, the holograms are in the form of numerical data that can be recorded, transmitted, and processed with digital techniques. On top of that, the availability of high capacity digital storage and wide-band communication technologies also cast light on the emergence of real time video holographic systems, enabling animated 3-D contents to be encoded as holographic data, and distributed via existing medium. At present, development in DH has reached a reasonable degree of maturity, but at the same time the heavy computation involved also imposes difficulty in practical applications. In this paper, a summary on a number of successful accomplishments that have been made recently in overcoming this problem is presented. Subsequently, we shall propose an economical framework that is suitable for real time generation and transmission of holographic video signals over existing distribution media. The proposed framework includes an aspect of extending the depth range of the object scene, which is important for the display of large-scale objects. [ABSTRACT FROM AUTHOR]

A method of digital filtering for eliminating the twin-image noise of reconstructed images in optical scanning holography is proposed and demonstrated by the example of slit objects. The fringe number of the scanning beam in relation to the twin-image noise is investigated in detail. Some results of computer simulations are obtained. In the far field, the further object scanned by the scanning beam with fewer fringes has lower and flatter amplitude of the twin-image noise for reconstructed images. However, being independent of the fringe number the twin-image noise affects seriously on the reconstruction in the near field. So the twin-image noise should be considered in reconstruction in the near field. [ABSTRACT FROM AUTHOR]