Indirect Imaging Methods Research Articles

Computational Imaging Encryption with a Steganographic and Holographic Authentication Strategy

AbstractRobust data security is of paramount importance, particularly for highly classified information. To achieve this, advanced encryption and decryption methods, along with stringent access control and physical security measures, are essential to mitigate the risk of unauthorized access and data exposure. Ghost imaging (GI), a computational imaging technique that operates indirectly, offers a distinct approach compared to traditional spatially resolved imaging techniques. By utilizing computational algorithms, GI enables indirect image reconstruction, making it well‐suited for encryption applications. This proposal introduces a new computational imaging encryption scheme that combines Fourier ghost imaging (FGI) and computational holography. The scheme utilizes an untrained‐tree‐network to generate two camouflaged computer‐generated holograms (CGHs). Integration of CGH‐based steganography and holographic authentication enhances the encoding and decoding processes of FGI encryption. The effectiveness and security of the proposed scheme are rigorously validated through numerical simulations and optical experiments. The results demonstrate promising potential for effectively merging direct and indirect imaging methods in security applications.

600-GHz Fourier imaging based on heterodyne detection at the 2nd sub-harmonic.

Fourier imaging is an indirect imaging method which records the diffraction pattern of the object scene coherently in the focal plane of the imaging system and reconstructs the image using computational resources. The spatial resolution, which can be reached, depends on one hand on the wavelength of the radiation, but also on the capability to measure - in the focal plane - Fourier components with high spatial wave-vectors. This leads to a conflicting situation at THz frequencies, because choosing a shorter wavelength for better resolution usually comes at the cost of less radiation power, concomitant with a loss of dynamic range, which limits the detection of higher Fourier components. Here, aiming at maintaining a high dynamic range and limiting the system costs, we adopt heterodyne detection at the 2nd sub-harmonic, working with continuous-wave (CW) radiation for object illumination at 600 GHz and local-oscillator (LO) radiation at 300 GHz. The detector is a single-pixel broad-band Si CMOS TeraFET equipped with substrate lenses on both the front- and backside for separate in-coupling of the waves. The entire scene is illuminated by the object wave, and the Fourier spectrum is recorded by raster scanning of the single-detector unit through the focal plane. With only 56 µW of power of the 600-GHz radiation, a dynamic range of 60 dB is reached, sufficient to detect the entire accessible Fourier space spectrum in the test measurements. We present a detailed comparison between plane-to-plane imaging and Fourier imaging, and show that, with both, a lateral spatial resolution of better than 0.5 mm, at the diffraction limit, is reached.

Characterization of near-field emission and structure of an SLD by polarization parametric indirect microscopic imaging

In this paper, a novel polarization parametric indirect microscopic imaging (PIMI) method is utilized for the first time to characterize the near-field emission mode and end-face structure of nanoscale semiconductor light-emitting chips. Via polarization modulation and detection of the emitted light from an superluminescent diode chip, abundant information including the distinct border of the emission mode, which cannot be seen by the traditional method, is collected and visualized as the form of multi-dimensional photon state distribution images. The polarization property distribution of the emission mode was visualized for the first time. Besides, by concurrent analysis of PIMI images of the end-face structure and emission mode, potential impurities adhered to the emitting facet can be precisely screened and located. The proposed method here has considerable advantages in the characterization of the light-emitting devices, paving a new way for precise, convenient, cost-effective, and large-scale quality inspection in industries.

Positive Jacobian constraints for elliptic boundary value problems with piecewise-regular coefficients arising from multi-wave inverse problems

Multi-wave inverse problems are indirect imaging methods using the interaction of two different imaging modalities. One brings spatial accuracy, and the other contrast sensitivity. The inversion method typically involve two steps. The first step is devoted to accessing internal datum of quantities related to the unknown parameters being observed. The second step involves recovering the parameters themselves from the internal data. To perform that inversion, a typical requirement is that the Jacobian of fields involved does not vanish. A number of authors have considered this problem in the past two decades, and a variety of methods have been developed. Existing techniques require Hölder continuity of the parameters to be reconstructed. In practical applications, the medium may present embedded elements, with distinct physical properties, leading to discontinuous coefficients. In this article we explain how a Jacobian constraint can be imposed in the piecewise regular case, when the physical model is a divergence form second order linear elliptic boundary value problem.

Implementation of a Large-Area Diffractive Lens Using Multiple Sub-Aperture Diffractive Lenses and Computational Reconstruction

Direct imaging systems that create an image of an object directly on the sensor in a single step are prone to many constraints, as a perfect image is required to be recorded within this step. In designing high resolution direct imaging systems with a diffractive lens, the outermost zone width either reaches the lithography limit or the diffraction limit itself, imposing challenges in fabrication. However, if the imaging mode is switched to an indirect one consisting of multiple steps to complete imaging, then different possibilities open. One such method is the widely used indirect imaging method with Golay configuration telescopes. In this study, a Golay-like configuration has been adapted to realize a large-area diffractive lens with three sub-aperture diffractive lenses. The sub-aperture diffractive lenses are not required to collect light and focus them to a single point as in a direct imaging system, but to focus independently on different points within the sensor area. This approach of a Large-Area Diffractive lens with Integrated Sub-Apertures (LADISA) relaxes the fabrication constraints and allows the sub-aperture diffractive elements to have a larger outermost zone width and a smaller area. The diffractive sub-apertures were manufactured using photolithography. The fabricated diffractive element was implemented in indirect imaging mode using non-linear reconstruction and the Lucy–Richardson–Rosen algorithm with synthesized point spread functions. The computational optical experiments revealed improved optical and computational imaging resolutions compared to previous studies.

Nonlinear Reconstruction of Images from Patterns Generated by Deterministic or Random Optical Masks-Concepts and Review of Research.

Indirect-imaging methods involve at least two steps, namely optical recording and computational reconstruction. The optical-recording process uses an optical modulator that transforms the light from the object into a typical intensity distribution. This distribution is numerically processed to reconstruct the object’s image corresponding to different spatial and spectral dimensions. There have been numerous optical-modulation functions and reconstruction methods developed in the past few years for different applications. In most cases, a compatible pair of the optical-modulation function and reconstruction method gives optimal performance. A new reconstruction method, termed nonlinear reconstruction (NLR), was developed in 2017 to reconstruct the object image in the case of optical-scattering modulators. Over the years, it has been revealed that the NLR can reconstruct an object’s image modulated by an axicons, bifocal lenses and even exotic spiral diffractive elements, which generate deterministic optical fields. Apparently, NLR seems to be a universal reconstruction method for indirect imaging. In this review, the performance of NLR isinvestigated for many deterministic and stochastic optical fields. Simulation and experimental results for different cases are presented and discussed.

Detection of virus particles by scattering field using the multiperspective polarization modulation imaging method

The polarization parametric indirect microscopic imaging (PIMI) method, which employs a polarization-modulated incidence illumination and fitting the far-field variation of polarization states of scattered photons, is capable of direct identification of subdiffraction-scale structures and substances, such as virus particles. However, in the present strategy, the optical elements that collect the scattered photons are nearly fixed above the sample, making the collected information relatively limited, as the side-scattering photons are not fully utilized. To address this problem, we propose a multiperspective PIMI imaging method to maximize the collection of scattering photons from different spatial directions, which can obtain more information of optical anisotropy among particles. As a proof-of-concept study, virus detection using such a method is performed theoretically and experimentally. Results reveal that the virus particles can be detected and determined more distinctly thanks to the set of PIMI images from different spatial angles, showing notable superiority to the previous scheme, where only a plane PIMI image is derived from a fixed spatial direction. With the capability of acquiring more characteristics of the samples, the proposed multiperspective PIMI method can be applied in many fields, such as morphological characterization and biosensing.

Metasurface-based key for computational imaging encryption.

Optical metasurfaces can offer high-quality multichannel displays by modulating different degrees of freedom of light, demonstrating great potential in the next generation of optical encryption and anti-counterfeiting. Different from the direct imaging modality of metasurfaces, single-pixel imaging (SPI) as a typical computational imaging technique obtains the object image from a decryption-like computational process. Here, we propose an optical encryption scheme by introducing metasurface-images (meta-images) into the encoding and decoding processes as the keys of SPI encryption. Different high-quality meta-images generated by a dual-channel Malus metasurface play the role of keys to encode multiple target images and retrieve them following the principle of SPI. Our work eliminates the conventional digital transmission process of keys in SPI encryption, enables the reusability of a single metasurface in different encryption processes, and thereby paves the way toward a high-security optical encryption between direct and indirect imaging methods.

Digital imaging and dental record

One of the most important developments in the field of radiology is that the imaging process has started to take place in the digital environment. The advantages of digital radiography increase the interest of dentists to digital radiography, and nowadays digital systems are replacing conventional systems. The most important reasons for the increase of using the digital systems are the fast access to the image, the quality of the image, and the easy storage and transmission of the image. Nowadays, the clinicians can digitize anything and recall it with the patient. This article presents a review about digital imaging and dental record. The history of digital imaging, direct and indirect digital imaging methods, digital sensors and dental record were reviewed.

White light three-dimensional imaging using a quasi-random lens.

Coded aperture imaging (CAI) technology is a rapidly evolving indirect imaging method with extraordinary potential. In recent years, CAI based on chaotic optical waves have been shown to exhibit multidimensional, multispectral, and multimodal imaging capabilities with a signal to noise ratio approaching the range of lens based direct imagers. However, most of the earlier studies used only narrow band illumination. In this study, CAI based on chaotic optical waves is investigated for white light illumination. A numerical study was carried out using scalar diffraction formulation and correlation optics and the lateral and axial resolving power for different spectral width were compared. A binary diffractive quasi-random lens was fabricated using electron beam lithography and the lateral and axial point spread holograms are recorded for white light. Three-dimensional imaging was demonstrated using thick objects consisting of two planes. An integrated sequence of signal processing tools such as non-linear filter, low-pass filter, median filter and correlation filter were applied to reconstruct images with an improved signal to noise ratio. A denoising deep learning neural network (DLNN) was trained using synthetic noisy images generated by the convolution of recorded point spread functions with the virtual object functions under a wide range of aberrations and noises. The trained DLNN was found to reduce further the reconstruction noises.

大视场Ritchey-Chretien光学系统的间接成像方法

大视场Ritchey-Chretien光学系统的间接成像方法

Gadoxetic acid-enhanced MR imaging for hepatocellular carcinoma: molecular and genetic background.

Gadoxetic acid-enhanced magnetic resonance imaging (MRI) plays important roles in diagnosis of hepatic lesions because of its superiority in the detectability of small lesions, its differentiation ability, and its utility for the early diagnosis of hepatocellular carcinoma (HCC). In HCC, expression of organic anion transporting polypeptide (OATP) 1B3 correlates with the enhancement ratio in the hepatobiliary phase. Gadoxetic acid-enhanced MRI, an indirect molecular imaging method, reflects OATP1B3 expression in HCC. OATP1B3 expression gradually decreases from the dysplastic nodule stage to advanced HCC. Decreased expression is a sensitive marker of multistep hepatocarcinogenesis, especially in the early stages. Hypervascular HCCs commonly show hypointensity in the hepatobiliary phase corresponding to a decrease in OATP1B3; however, approximately 10% of HCCs show hyperintensity due to OATP1B3 overexpression. This hyperintense HCC shows less aggressive biological features and has a better prognosis than hypointense HCC. Hyperintense HCC can be classified into a genetic subtype of HCC with a mature hepatocyte-like molecular expression. OATP1B3 expression and the less aggressive nature of hyperintense HCC are regulated by the molecular interaction of β-catenin signaling and hepatocyte nuclear factor 4α, a tumor suppressor factor. Gadoxetic acid-enhanced MR imaging has the potential to be an imaging biomarker for HCC. KEY POINTS: • The hepatobiliary phase is a sensitive indirect indicator of organic anion transporting polypeptide1B3 (OATP1B3) expression in hepatocellular carcinoma (HCC). • The OATP1B3 expression, namely, enhancement in the hepatobiliary phase, decreases from the very early stage of hepatocarcinogenesis, contributing to early diagnosis of HCC. • HCC showing hyperintensity on the hepatobiliary phase is a peculiar genetic subtype of HCC with OATP1B3 overexpression, a less aggressive nature, and mature hepatocyte-like molecular/genetic features.

Direct evidence of non-disk optical continuum emission around an active black hole

Accretion onto black holes is key to their growth over cosmic time1, especially during the active galactic nuclei phase when the inflowing material forms a radiatively efficient accretion disk2. To probe the disk, indirect imaging methods such as reverberation mapping3–6 and microlensing7,8 are required. Recent findings suggest that the disk may be larger than theoretical predictions by a factor of a few4,6,9, thus casting doubt on our understanding of accretion in the general astrophysical context. Whether new physics is implied10–12 or poorly understood biases are in effect5,6,13,14 is a longstanding question. Here, we report new reverberation data based on a unique narrowband-imaging design15, and argue that time delays between adjacent optical bands are primarily associated with the reprocessing of light by a farther away under-appreciated non-disk component. This component is associated with high-density photoionized material that is uplifted from the outer accretion disk, probably by radiation-pressure force on dust, and thus may represent the long-sought origin of the broad-line region16. Our findings suggest that the optical phenomenology of some active galactic nuclei may be substantially affected by non-disk continuum emission with implications for measuring the fundamental properties of black holes and their active environs over cosmic time. New variability data of the accretion disk in active galactic nuclei argue for the existence of a farther away under-appreciated non-disk component associated with high-density photoionized material that is uplifted from the outer accretion disk.

Computational ghost imaging and ghost diffraction in turbulent ocean

Computational ghost imaging (CGI) is an indirect single-pixel imaging method that can retrieve an image of an object in a hostile environment by using a correlation of intensity fluctuations. Based on the theory of ghost imaging (GI) and using the spatial power spectrum of the refractive index of ocean water, we develop a unified imaging formula for the CGI and computational ghost diffraction (CGD) operating through oceanic turbulence, and numerically analyse how the image quality can be affected by oceanic turbulence including the rate of dissipation of turbulent kinetic energy per unit mass of fluid, the rate of dissipation of mean-square temperature, and the relative strength of temperature salinity fluctuations, as well as the propagation distance. To quantitatively evaluate the quality of the retrieved images, the relative mean square error is employed in the CGI system. Our results show that the quality of the CGI scheme operating through oceanic turbulence is closely related to the propagation distance. When the propagation distance is fixed to be relatively small, we can effectively obtain a sharp image in the case of strong turbulence, and the turbulence influence can be neglected. Meanwhile the turbulence effects become more serious in the CGI system with increasing propagation distance. Besides, we find the CGI system is more robust against oceanic turbulence than the CGD system.

Digital Holography as Computer Vision Position Sensor with an Extended Range of Working Distances.

Standard computer vision methods are usually based on powerful contact-less measurement approaches but applications, especially at the micro-scale, are restricted by finite depth-of-field and fixed working distance of imaging devices. Digital holography is a lensless, indirect imaging method recording the optical wave diffracted by the object onto the image sensor. The object is reconstructed numerically by propagating the recorded wavefront backward. The object distance becomes a computation parameter that can be chosen arbitrarily and adjusted to match the object position. No refractive lens is used and usual depth-of-field and working distance limitations are replaced by less restrictive ones tied to the laser-source coherence-length and to the size and resolution of the camera sensor. This paper applies digital holography to artificial visual in-plane position sensing with an extra-large range-to-resolution ratio. The object is made of a pseudoperiodic pattern allowing a subpixel resolution as well as a supra field-of-observation displacement range. We demonstrate an in-plane resolution of 50 nm and deg. in X, Y and respectively, over a working distance range of more than 15 cm. The allowed workspace extends over . Digital holography extends the field of application of computer vision by allowing an extra-large range of working distances inaccessible to refractive imaging systems.

ULTRASONOGRAPHY OF THE EXTERNAL REPRODUCTIVE ORGANS IN TOM

This study aims to delineate the tissue structure of male cat external reproductive organs using ultrasound with different types of consoles and transducers frequencies through indirect method. External organ of 5 tom weighing 2-3 kg was evaluated using ultrasound with stationary console (linear transducer, 10 MHz) and portable console (linear transducer, 6.5 MHz), transcutaneously. The results showed that both console and transducer could not visualize the structure of organs sized less than 10 mm through direct method. However, the indirect method using stationary console with a 10 MHz transducer enable to visualize the organ and depicts clearly the internal organ structure such as penis and its parts, scrotum and its constituent layers, caput and cauda of epididymis, and testicles. Furthermore, portable console with 6.5 MHz transducer was still able to provide an adequate image of those organs. In general, fibrous tissues such as tunica vaginalis, tunica Dartos, funiculusspermaticus, and urethra were visible in ultrasonogram as hyperechoic structures, while soft tissues such as the parts of testicles and penis were visible as hypoechoic structures. Tissue containing fluid such as urethral lumen was visible as anechoic structure. In conclusion, indirect ultrasound imaging method was sufficient to visualize the organs sized less than 10 mm using 3-15 MHz transducer in which was currently widely used in animal health care clinics.

Improving the extinction bandwidth of MMI chalcogenide photonic chip based MIR nulling interferometers.

Research into planets beyond our own star system has until recently relied on indirect imaging methods. Direct imaging methods are now establishing a foothold in the hunt for alien planets and habitable worlds. Nulling interferometry is a promising approach for suppressing the host star brightness and resolving surrounding planets. A key requirement in this method is the interference of light from multiple telescopes/baselines and free space optical devices have already rendered images of other worlds. Photonic chip based systems are also becoming accepted as means of accomplishing this but require, in particular, wide bandwidth, high precision on chip beam splitters. In this paper a design improvement is outlined to one of the most fabrication tolerant integrated beam splitter components that significantly increases its coupling bandwidth and therefore its bandwidth at high extinction. Preliminary experimental results from a fabricated device are also shown. The predicted bandwidth spans 3.8 - 4.1 μm at an extinction of ∼50 dB but at the expense of increasing the loss to 0.6 dB in transmission.

Identification of a Retinal Circuit for Recurrent Suppression Using Indirect Electrical Imaging

Understanding the function of modulatory interneuron networks is a major challenge, because such networks typically operate over long spatial scales and involve many neurons of different types. Here, we use an indirect electrical imaging method to reveal the function of a spatially extended, recurrent retinal circuit composed of two cell types. This recurrent circuit produces peripheral response suppression of early visual signals in the primate magnocellular visual pathway. We identify a type of polyaxonal amacrine cell physiologically via its distinctive electrical signature, revealed by electrical coupling with ON parasol retinal ganglion cells recorded using a large-scale multi-electrode array. Coupling causes the amacrine cells to fire spikes that propagate radially over long distances, producing GABA-ergic inhibition of other ON parasol cells recorded near the amacrine cell axonal projections. We propose and test a model for the function of this amacrine cell type, in which the extra-classical receptive field of ON parasol cells is formed by reciprocal inhibition from other ON parasol cells in the periphery, via the electrically coupled amacrine cell network.

Structure of an Ancient Egyptian Tomb Inferred from Ground‐Penetrating Radar Imaging of Deflected Overburden Horizons

AbstractGeophysical data acquisitions in most archaeological campaigns aim to image the target structure directly. The presence of a target, however, may be inferred from its interaction with surrounding layers, if its relationship with those layers can be characterized sufficiently. In this paper, we show the use of ground‐penetrating radar (GPR) to detect the subsurface continuation of the Ancient Egyptian tomb of the high‐official Karakhamun (Theban Tomb 223) at the South Asasif tomb complex (Luxor, Egypt). Data were acquired using a Sensors & Software pulseEKKO PRO system, equipped with antennas of 500 MHz centre‐frequency, on a silty–sandy sediment surface directly over the target structure. A test vertical radar profile (VRP) suggested that the tomb superstructure was buried too deeply beneath sedimentary overburden to be imaged directly: 500 MHz energy would propagate for only ~2 m before becoming undetectable. Attenuative layers within that overburden were strongly reflective, however, and could be used to provide indirect evidence of any underlying structure. When observed in the GPR grid, these layers showed a discrete zone of deflection, ~0.9 m in amplitude and ~4 m wide, aligned with the long‐axis of the tomb. This deflection was attributed either to a collapsed vestibule beneath the survey site, or sediment settling within an unroofed staircase descending from ground‐ to tomb‐floor‐level; supporting evidence of this was obtained towards the end of the excavation campaign and in the following year. We highlight the value of such indirect imaging methods as a potential means of improving the capabilities of a given geophysical survey system, in this case allowing the GPR to characterize a target at greater depth than would typically be considered practical. © 2014 The Authors. Archaeological Prospection published by John Wiley & Sons Ltd.

FIRST IMAGES FROM THE FOCUSING OPTICS X-RAY SOLAR IMAGER

The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket payload flew for the first time on 2012 November 2, producing the first focused images of the Sun above 5 keV. To enable hard X-ray (HXR) imaging spectroscopy via direct focusing, FOXSI makes use of grazing-incidence replicated optics combined with fine-pitch solid-state detectors. On its first flight, FOXSI observed several targets that included active regions, the quiet Sun, and a GOES-class B2.7 microflare. This Letter provides an introduction to the FOXSI instrument and presents its first solar image. These data demonstrate the superiority in sensitivity and dynamic range that is achievable with a direct HXR imager with respect to previous, indirect imaging methods, and illustrate the technological readiness for a spaceborne mission to observe HXRs from solar flares via direct focusing optics.