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I suggest an irregular aperture and calculate the impulse response, or the point spread function (PSF) corresponding to this aperture. In addition, I calculated the PSF in the case of rotated irregular apertures. Secondly, I apply these irregular apertures to the confocal scanning laser microscope (CSLM). I obtained the images using the CSLM provided with irregular apertures and compared them with the case of uniform circular apertures. Finally, I differentiate speckle images that were obtained using different orientations of the irregular aperture. Then, I reconstructed the irregular aperture at different orientations from the speckle pattern. [ABSTRACT FROM AUTHOR]

The sheet metal surface crack detection during manufacturing is an essential issue because of both the product quality and process productivity. Development of solutions to eliminate defective products during the metal forming process is crucial for the smooth production and for developing an appropriate tool geometry in the initial phase of the process. Currently, the methods of surface crack detection used in the industry are mostly related to visual inspection. These are methods that require operators of industrial facilities considerable attention and effort to capture emerging discontinuities on the sheet metal surface. Also, this situation results increase in the duration of the specific operations of stamping and significantly reduces productivity. Therefore, an industrial application of a non-contact laser technique that simultaneously provides the results of the speckle imaging is presented. The authors demonstrate a specially designed machine vision system along with experimental tools for the stamping operation. Proposed solution uses the phenomenon of speckle pattern that appears in the image of the investigated sheet surface produced by the laser beam emission. In this method, coherent laser light is emitted to the surface, where a speckle pattern is generated due to scatter reflection from the sheet metal surface and then, shift-and-add technique and image processing is applied. The proposed measurement technique consists, initially, of making a sequence of images of the tested object for the moving surface of the sheet. Secondly, the object's displacement quantity in each image is determined, and the position is corrected. The test object in each image is moved to the starting position, and all images are superimposed. It allows to obtain a high-quality image with visible surface defects. Finally, the dynamically changing speckle pattern intensity is evaluated using Gaussian-of-Laplacian edge detection to investigate a surface crack location due to the surface discontinues and light scattering. This process is recommended for machine vision imaging of distant objects, which works well in industrial conditions as well as online analysis. Also, from the speckle size measurement, an experimental procedure is employed to verify the best condition for vision system resolution.

We presented a low-cost electronic speckle imaging method for quantifying and monitoring the moderate expansion and contraction of fluids. The system comprises the steps of recording a stack of electronic speckle patterns of the liquid under coherent light illumination, generating velocity vector fields of the temporal dynamic speckle sequence, calculating profile velocity at different temperatures of the liquid, evaluating the inertia moment (IM) of the temporal history of speckle patterns followed by the computation of the co-occurrence matrices. The results show that profile velocity at different temperatures may be used to determine the liquid's thermal state. The test evaluated speckle grain size as a potential criterion for monitoring the liquid's moderate thermal expansion and allowed for the measurement of thermal exchange between the system and its surroundings even at very low temperatures (4 °C). The experiment demonstrates the effectiveness of the laser speckle imaging technique at the macro- and micro-scale molecular dynamics levels. [ABSTRACT FROM AUTHOR]

The sheet metal surface crack detection during manufacturing is an essential issue because of both the product quality and process productivity. Development of solutions to eliminate defective products during the metal forming process is crucial for the smooth production and for developing an appropriate tool geometry in the initial phase of the process. Currently, the methods of surface crack detection used in the industry are mostly related to visual inspection. These are methods that require operators of industrial facilities considerable attention and effort to capture emerging discontinuities on the sheet metal surface. Also, this situation results increase in the duration of the specific operations of stamping and significantly reduces productivity. Therefore, an industrial application of a non-contact laser technique that simultaneously provides the results of the speckle imaging is presented. The authors demonstrate a specially designed machine vision system along with experimental tools for the stamping operation. Proposed solution uses the phenomenon of speckle pattern that appears in the image of the investigated sheet surface produced by the laser beam emission. In this method, coherent laser light is emitted to the surface, where a speckle pattern is generated due to scatter reflection from the sheet metal surface and then, shift-and-add technique and image processing is applied. The proposed measurement technique consists, initially, of making a sequence of images of the tested object for the moving surface of the sheet. Secondly, the object's displacement quantity in each image is determined, and the position is corrected. The test object in each image is moved to the starting position, and all images are superimposed. It allows to obtain a high-quality image with visible surface defects. Finally, the dynamically changing speckle pattern intensity is evaluated using Gaussian-of-Laplacian edge detection to investigate a surface crack location due to the surface discontinues and light scattering. This process is recommended for machine vision imaging of distant objects, which works well in industrial conditions as well as online analysis. Also, from the speckle size measurement, an experimental procedure is employed to verify the best condition for vision system resolution. [ABSTRACT FROM AUTHOR]

Imaging using scattering media is a very important yet challenging technology. As one of the most widely used scattering imaging methods, speckle autocorrelation technology has important applications in several fields. However, traditional speckle autocorrelation imaging methods usually use iterative phase recovery algorithms to obtain the Fourier phase of hidden objects, posing issues such as large data calculation volumes and uncertain reconstruction results. Here, we propose a single-shot scattering imaging method based on the bispectrum truncation method. The bispectrum analysis is utilized for hidden object phase recovery, the truncation method is used to avoid the computation of redundant data when calculating the bispectrum data, and the method is experimentally verified. The experimental results show that our method does not require uncertain iterative calculations and can reduce the bispectrum data computation by more than 80% by adjusting the truncation factor without damaging the imaging quality, which greatly improves imaging efficiency. This method paves the way for rapid imaging through scattering media and brings benefits for imaging in dynamic situations.

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

During the last century, fluorescence microscopy has played a pivotal role in a range of scientific discoveries. The success of fluorescence microscopy has prevailed despite several shortcomings like measurement time, photobleaching, temporal resolution, and specific sample preparation. To bypass these obstacles, label-free interferometric methods have been developed. Interferometry exploits the full wavefront information of laser light after interaction with biological material to yield interference patterns that contain information about structure and activity. Here, we review recent studies in interferometric imaging of plant cells and tissues, using techniques such as biospeckle imaging, optical coherence tomography, and digital holography. These methods enable quantification of cell morphology and dynamic intracellular measurements over extended periods of time. Recent investigations have showcased the potential of interferometric techniques for precise identification of seed viability and germination, plant diseases, plant growth and cell texture, intracellular activity and cytoplasmic transport. We envision that further developments of these labelfree approaches, will allow for high-resolution, dynamic imaging of plants and their organelles, ranging in scales from sub-cellular to tissue and from milliseconds to hours. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The objective of this paper is to develop a method for visualizing the onset of skin layer formation at the gas-liquid interface during the evaporation of a water-based pigment ink filled in a narrow space such as the nozzle of an inkjet printhead. We developed two methods to visualize the surface and depth-wise distributions of the diffusion coefficient near the edge of a glass capillary filled with aqueous colloidal solution by using measurements based on the dynamic light scattering method. One method generates laser speckles at the gas-liquid interface of the ink, which are analyzed to determine the temporal changes in the surface distribution of particle diffusion coefficients. Another method uses an optical coherence tomography method to acquire cross-sectional images of the ink in the depth-wise direction, and analyzes the speckles that appear on the images to determine the temporal change in the depth distribution of the particle diffusion coefficient. It was observed that, depending on the type of hardly volatile solvent in ink, there are cases where the diffusion coefficient changes while remaining spatially uniform, and other cases where the diffusion coefficient differs remarkably near the gas-liquid interface. Since the motion of particles in the ink can be visualized in three dimensions, although pseudo-lightly, it has been possible to detect signs of skin layer formation.

Abstract Background A design of equally spaced eight-circles placed at equal distances from the origin is suggested. Three models corresponding to the eight-circle design considering conic, linear, and quadratic distributions are investigated. This arrangement is considered for the sake of improving both microscope resolution and image contrast as compared with the pure annular aperture. This design is different compared with other recent work on aperture modulation. Results and discussions The point spread function (PSF) is computed in all the models using the fast Fourier transform (FFT) algorithm that computes the discrete Fourier transform (DFT) corresponding to the models and compared with the corresponding PSF in the case of uniform circular aperture. In addition, the autocorrelation images for the apertures are shown differently. It is shown smooth pattern for the circular arrangement as compared with the deformation and shrinking appeared in the central peak in case of conic model. Finally, the speckle images corresponding to the considered apertures are investigated. Reconstructed apertures are obtained from the speckle images using the FFT algorithm. Conclusions The PSF is computed for the described models, and the autocorrelation corresponding to the apertures showed difference. The reconstructed apertures from the speckle images can be improved using filtering techniques. It is noted that MATLAB codes are constructed in the computations of all images and plots.

A dynamic functional piecewise laser speckle temporal contrast imaging (PW-LSTCI) modality is proposed to show the dynamic blood flow in the macro and micro circulations. Research shows that there is always a transition point related to contact time, which separates the positive growth trend of high velocity from the negative growth trend of small velocity. It can be found that the series of transition points with the corresponding exposure time follow an exponential pattern, indicating that the increase in the exposure time is accompanied by the decrease in the value of transition point. The changes of earflap blood flow in root artery circulation induced by occlusion and reperfusion in mice are imaged to observe the existence of transition points and their effects on slow and fast dynamic blood flow imaging. The study is valuable for noninvasive imaging of microcirculation and plays an important role in dynamic functional imaging of vascular system. [ABSTRACT FROM AUTHOR]

Using 3 years of observations with the Zorro and ’Alopeke speckle interferometric instruments at Gemini South and North, respectively, we present an analysis of the sensitivity of the data taken in two narrow-band optical filters centered at 562 and 832 nm (widths of 54 and 40 nm, respectively). In this paper we focus on model calculations of the predicted signal-to-noise values achievable and the results of over 2500 actual observations. We find that S/N values of several 100 are easily achieved, but that the sky background during full moon is a very limiting factor in the observations, especially those performed in the short-wavelength (blue) optical spectral range and for targets fainter than R ∼14. A comparison of our Gemini speckle observations over six observing semesters reveals that red band-pass observations provide more robust results in general, likely due to better atmospheric performance at these wavelengths. Using the identical instruments on Gemini North and South, we find that similar results are obtained, yielding typical contrast limits of 5-9 magnitudes from the diffraction limit out to 1.2″ for a range of target brightness (optical magnitudes from ∼ 3 to >16). Using our S/N model along with the observational results, an estimation of the contrast limits achievable for a given observation can be predicted based on the target brightness, sky illumination and seeing conditions, and the total integration time.

Fluorescence imaging through ultrathin fibers is a promising approach to obtain high-resolution imaging with molecular specificity at depths much larger than the scattering mean-free paths of biological tissues. Such imaging techniques, generally termed lensless endoscopy, rely upon the wavefront control at the distal end of a fiber to coherently combine multiple spatial modes of a multicore (MCF) or multimode fiber (MMF). Typically, a spatial light modulator (SLM) is employed to combine hundreds of modes by phase-matching to generate a high-intensity focal spot. This spot is subsequently scanned across the sample to obtain an image. We propose here a novel scanning scheme, partial speckle scanning (PSS), inspired by compressive sensing theory, that avoids the use of an SLM to perform fluorescent imaging with optical fibers with reduced acquisition time. Such a strategy avoids photo-bleaching while keeping high reconstruction quality. We develop our approach on two key properties of the MCF: (i) the ability to easily generate speckles, and (ii) the memory effect that allows one to use fast scan mirrors to shift light patterns. First, we show that speckles are subexponential random fields. Despite their granular structure, an appropriate choice of the reconstruction parameters makes them good candidates to build efficient sensing matrices. Then, we numerically validate our approach and apply it on experimental data. The proposed sensing technique outperforms conventional raster scanning: higher reconstruction quality is achieved with far fewer observations. For a fixed reconstruction quality, our speckle scanning approach is faster than compressive sensing schemes which require changing the speckle pattern for each observation. [ABSTRACT FROM AUTHOR]

We have previously presented a blood perfusion parameter by means of the spatial contrast of speckle patterns observed for blood perfusion in skin tissue and a blood vessel. This parameter permits us to visualize a relative blood perfusion distribution from a single speckle pattern. Therefore, it can estimate the blood perfusion with a frame rate of an imaging device employed. This parameter is, however, dependent on the speckle size and the condition of image processing of speckle patterns. In the present study, we estimated this condition with relation to the speckle size for obtaining high sensitivity and good linearity of the parameter to the blood perfusion. Experiments were conducted for ground-glass model, flow model and human wrist to investigate perfusion sensing characteristics of the present parameter. [ABSTRACT FROM AUTHOR]

• Simultaneous quantification of skin thickness and microcirculatory flow rate is reported for the first-time using laser speckle image analysis. • The experiments were carried out on a flow phantom with physiologically relevant measures for skin thickness, scatterer concentration and flow rate, specific to healthy and scleroderma tissue. • A multiparametric model is devised for classifying tissue status after a comprehensive analysis of the extracted speckle parameters. • This approach can be extended to other physical / biological models as well where the extracted speckle parameters are interlinked with structural and functional sample properties. Scleroderma is an autoimmune disorder caused by increased collagen deposition in the dermal layer of skin, which alters the dermal layer's thickness, affecting the local perfusion. In this article, we aim to build an experimental model to simultaneously quantify the dermal thickness and perfusion changes during scleroderma progression through a comprehensive analysis of various static and dynamic laser speckle image parameters. [ABSTRACT FROM AUTHOR]

Target tracking and imaging through scattering media are challenges that must be overcome for important applications in various fields. The fundamental problem is the randomly diffused light in scattering media that prevents the formation of diffraction-limited images. In recent years, speckle correlation has emerged as a powerful approach for restoring targets through scattering media and tracking targets with high scattering. However, this method fails to achieve high-accuracy target tracking in multidimensional motion. Furthermore, retrieving the deterministic phase of a target in a low-resolution speckle pattern is limited. Here, a method based on speckle-difference-combined bispectrum analysis (SDCBA) is presented to simultaneously track and image targets. The proposed SDCBA requires no high-resolution pattern, randomly assigned initial values, nor numerous iterations. The target is tracked simultaneously in multidimension by using speckle difference autocorrelation and restored with the deterministic phase via bispectrum analysis of the low-resolution speckle pattern. This work carries out simulations and experiments to demonstrate simultaneous multidimensional target tracking and imaging in low-resolution speckle pattern through scattering media via the SDCBA. This work will benefit various fields, including biomedical applications, materials science, and military security.

Optical coherence tomography is an emerging non-invasive technology that provides high resolution, cross-sectional tomographic images of internal structures of specimens. It holds great potentials for a wide variety of applications, especially in the field of biomedical imaging. OCT images, however, are usually degraded by significant speckle noise. Here we report a 3D approach to attenuating speckle noise in OCT images. This approach is based on the 3D curvelet transform, and is conveniently controlled by a single parameter that determines the threshold in the curvelet domain. Unlike 2D approaches which only consider information in individual images, 3D processing, by analyzing all images in a volume simultaneously, has the advantage of also taking the information between images into account. This, coupled with the curvelet transform's nearly optimal sparse representation of curved edges that are common in OCT images, provides a simple yet powerful platform for speckle attenuation. We show the approach suppresses a significant amount of speckle noise, and in the mean time preserves and thus reveals many subtle features that could get attenuated in other approaches. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Optical coherence tomography is an emerging non-invasive technology that provides high resolution, cross-sectional tomographic images of internal structures of specimens. It holds great potentials for a wide variety of applications, especially in the field of biomedical imaging. OCT images, however, are usually degraded by significant speckle noise. Here we report a 3D approach to attenuating speckle noise in OCT images. This approach is based on the 3D curvelet transform, and is conveniently controlled by a single parameter that determines the threshold in the curvelet domain. Unlike 2D approaches which only consider information in individual images, 3D processing, by analyzing all images in a volume simultaneously, has the advantage of also taking the information between images into account. This, coupled with the curvelet transform's nearly optimal sparse representation of curved edges that are common in OCT images, provides a simple yet powerful platform for speckle attenuation. We show the approach suppresses a significant amount of speckle noise, and in the mean time preserves and thus reveals many subtle features that could get attenuated in other approaches. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Target tracking and imaging through scattering media are challenges that must be overcome for important applications in various fields. The fundamental problem is the randomly diffused light in scattering media that prevents the formation of diffraction-limited images. In recent years, speckle correlation has emerged as a powerful approach for restoring targets through scattering media and tracking targets with high scattering. However, this method fails to achieve high-accuracy target tracking in multidimensional motion. Furthermore, retrieving the deterministic phase of a target in a low-resolution speckle pattern is limited. Here, a method based on speckle-difference-combined bispectrum analysis (SDCBA) is presented to simultaneously track and image targets. The proposed SDCBA requires no high-resolution pattern, randomly assigned initial values, nor numerous iterations. The target is tracked simultaneously in multidimension by using speckle difference autocorrelation and restored with the deterministic phase via bispectrum analysis of the low-resolution speckle pattern. This work carries out simulations and experiments to demonstrate simultaneous multidimensional target tracking and imaging in low-resolution speckle pattern through scattering media via the SDCBA. This work will benefit various fields, including biomedical applications, materials science, and military security. [ABSTRACT FROM AUTHOR]

• The laser speckle pattern scattered from a diffuse surface is used to track object surface motions and to extract object distance and orientation for system calibration. • The proposed system can track speckle motions resulting from microscopic in-plane displacements and out-of-plane rotations at a high accuracy (6.0 %) and repeatability (2.8 %) from a 30.7-m distance. • The system has high demonstrated tilt sensitivity down to 0.0006° and can simultaneously measure absolute macroscopic surface angles beyond 10°. • The proposed approach is suitable for measuring retroreflective surfaces, like traffic signs and number plates. Defocused Speckle Imaging (DSI) is a non-contact optical method that can measure multiaxial object motions at microscopic sensitivity using a simple and mechanically robust optical setup. The object surface is illuminated by a laser beam, and the scattered interference speckle pattern is tracked with a defocused camera. DSI measurement sensitivity increases with distance, and the sensitivity can be tuned by simple camera defocus adjustment. These characteristics make DSI an attractive choice for tracking remote objects in field conditions. However, the use of DSI for practical measurements is limited because the speckle signals due to linear and rotational surface motions mix together, and because the instrument calibration requires accurate object range and surface orientation parameters. To address these issues, the work described here combines two recently presented concepts: 1) a defocused camera pair, and 2) a diffraction-based self-calibration principle. The proposed approach was demonstrated by a series of self-calibrated multiaxial motion measurements performed at an extended (30.7-m) distance. The studied motions included in-plane displacements and out-of-plane rotations (tilts), whereas out-of-plane displacements and in-plane rotations were excluded. The experiments showed DSI's capability for high tilt sensitivity down to 0.0006°, standalone remote angle measurements, and suitability for retroreflective surfaces. The diffraction-based self-calibration approach could monitor sampling distances at a 6.4 % accuracy and the relative surface angles of 2.5–7.4° at a 0.2° accuracy. The defocused camera pair tracked microscopic in-plane displacements (400 µm) and very fine out-of-plane tilts (0.003°) at a high accuracy, with a maximum uncertainty of 6.0 %. The proposed DSI approach is particularly suited for monitoring large objects and for operating in hazardous environments. The findings pave a way for interesting new applications, like high-range remote angle measurements, high-sensitivity straightness measurements, and 3D-positioning utilizing retroreflective markers that already exist in the built infrastructure. [ABSTRACT FROM AUTHOR]

Background and Objectives: Pulsed dye laser (PDL) irradiation is the standard clinical treatment for vascular lesions. However, PDL treatment of port wine stain birthmarks (PWS) is variable and unpredictable. Photodynamic therapy (PDT) using benzoporphyrin derivative monoacid ring A (BPD) and yellow light may induce substantial vascular effects and potentially offer a more effective treatment. In this study, we utilize a rodent dorsal skinfold model to evaluate the vascular effects of BPD-PDT at 576 nm as compared to PDL. Study Design/Materials and Methods: A dorsal skinfold window was created on the backs of female Sprague-Dawley rats, allowing epidermal and subdermal irradiation and subdermal imaging. One mg/kg BPD was administered intravenously via a jugular venous catheter. Study groups were: control (no BPD, no light), PDL (585 nm, τ p 1.5 ms, 10 J/cm 2), and PDT (BPD + continuous wave irradiation (CW) at 576nm, τ p 16 min, 96 J/cm 2). Vessels were imaged and assessed for damage using laser speckle imaging (LSI) before, immediately after, and 18 hours post-intervention. Results: Epidermal irradiation was accomplished without blistering, scabbing or ulceration. PDL and PDT resulted in similar reductions in vascular perfusion 18 hours post-intervention (34.6% and 33.4%, respectively). Conclusions: BPD-PDT can achieve safe and selective vascular effects and may offer an alternative therapeutic option for treatment of hypervascular skin lesions including PWS birthmarks.

Background and Objectives: Pulsed dye laser (PDL) irradiation is the standard clinical treatment for vascular lesions. However, PDL treatment of port wine stain birthmarks (PWS) is variable and unpredictable. Photodynamic therapy (PDT) using benzoporphyrin derivative monoacid ring A (BPD) and yellow light may induce substantial vascular effects and potentially offer a more effective treatment. In this study, we utilize a rodent dorsal skinfold model to evaluate the vascular effects of BPD-PDT at 576 nm as compared to PDL. Study Design/Materials and Methods: A dorsal skinfold window was created on the backs of female Sprague-Dawley rats, allowing epidermal and subdermal irradiation and subdermal imaging. One mg/kg BPD was administered intravenously via a jugular venous catheter. Study groups were: control (no BPD, no light), PDL (585 nm, τ p 1.5 ms, 10 J/cm 2), and PDT (BPD + continuous wave irradiation (CW) at 576nm, τ p 16 min, 96 J/cm 2). Vessels were imaged and assessed for damage using laser speckle imaging (LSI) before, immediately after, and 18 hours post-intervention. Results: Epidermal irradiation was accomplished without blistering, scabbing or ulceration. PDL and PDT resulted in similar reductions in vascular perfusion 18 hours post-intervention (34.6% and 33.4%, respectively). Conclusions: BPD-PDT can achieve safe and selective vascular effects and may offer an alternative therapeutic option for treatment of hypervascular skin lesions including PWS birthmarks.

We introduce the quantitative phase imaging camera with a weak diffuser (QPICWD) as an effective scheme of quantitative phase imaging (QPI) based on normal microscope platforms. The QPICWD is an independent compact camera measuring object induced phase delay under low-coherence quasi-monochromatic illumination by examining the deformation of the speckle intensity pattern. By interpreting the speckle deformation with an ensemble average of the geometric flow, we can obtain the high-resolution distortion field via the transport of intensity equation (TIE). Since the phase measured by TIE is the generalized phase of the partially coherent image, rather than the phase of the measured object, we analyze the effect of illumination coherence and imaging numerical aperture (NA) on the accuracy of phase retrieval, revealing that the sample's phase can be reliably reconstructed under the conditions that the coherence parameter (the ratio of illumination NA to objective NA) of the Köhler illumination is between 0.3 and 0.5. We present some applications for the proposed design involving nondestructive optical testing of microlens array with nanometric thickness and imaging of fixed and live unstained HeLa cells. Since the designed QPI camera does not require any modification of the widely available bright-field microscope or additional accessories for its use, it is expected to be applied by the broader communities of biology and medicine.

We discuss the possibility that the contours or details of images can be obtained by using the low-spatial-frequency or high-spatial-frequency parts of the reference beam in ghost imaging. The influence of the threshold selection which is used to divide the reference pattern into low-frequency and high-frequency parts is quite different. With the increase of the threshold, the signal-to-noise ratio (SNR) of low-frequency ghost imaging increases firstly and then decreases, while SNR of high-frequency ghost imaging decreases gradually. Under a suitable threshold, the results are compared with those by directly filtering ghost-image from the traditional ghost imaging. It is shown that better imaging quality can be obtained by using our scheme. To further improve imaging quality, the method of subtracting background before correlation calculation is also presented. [ABSTRACT FROM AUTHOR]

Multi-frame blind deconvolution (MFBD) has been a cornerstone for ground-based space situational awareness of near-Earth satellites since the early 2000's. In 2011 a variation of the classic MFBD algorithm was introduced that required solving for fewer variables than in the classic algorithm, but which still used all the available data to constrain the solution. The initial application of the new approach, referred to as compact multi-frame blind deconvolution (CMFBD), was found to be significantly faster than MFBD, and showed an indication that it may be able to provide restorations of higher quality, i.e. fewer artifacts. Since its introduction, the CMFBD approach has become the foundation of several MFBD-based algorithms that have been developed for applications such as high-accuracy wave front sensing from image plane data, and imaging through strong turbulence: both of which contribute to space situational awareness by increasing the area of sky available for surveillance. Here we show that the performance of the CMFBD approach can be improved through the addition of a new "internal consistency" constraint on the estimated point-spread functions. [ABSTRACT FROM AUTHOR]

The reflection and transmission of coherent light from a biological system can yield information about its condition. In the case of blood exposed to the air, there is a change in the properties of the speckle patterns observed in the coagulation process. This can be studied by means of the rate of temporal variation, the contrast, and also the fractality of patterns. The fractality of the speckle pattern can be investigated by a fractal dimension, which can quantify a level of the complexity of platelet aggregation structure and a fibrin network formed in the process of blood coagulation. In addition, dynamic characteristics of a movement in blood also contain information on the progress of the coagulation process. Fractality and dynamic characteristics are investigated simultaneously for speckle patterns observed in the coagulation process of stored horse blood. Experimental results show the feasibility of the proposed method for detecting hemolysis and formation of platelet aggregation structure and the fibrin network during the coagulation process. [ABSTRACT FROM AUTHOR]

Abstract Optical imaging through scattering layers based on the 'memory effect' (ME) always suffers from a limited field of view. Here, we present a method that employs prior information to provide indispensable support for imaging behind a scattering medium, in which case the transversal distance between the targets is beyond the limited range determined by the ME. We experimentally demonstrate that given a known target, or even a light point-source, the other unknown object beyond the ME can be determined with only a single-shot camera image, even if the information of targets are mixed in the speckle pattern. Based on the same concept, we show that our technique is also capable of imaging extended object, whose size is larger than the limited range of ME. This work may have potential in practical applications such as imaging through turbulent medium or the biomedical imaging. [ABSTRACT FROM AUTHOR]

When waves propagate through a strongly scattering medium the energy is transferred to the incoherent wave part by scattering. The wave intensity then forms a random speckle pattern seemingly without much useful information. However, a number of recent physical experiments show how one can extract useful information from this speckle pattern. Here we present the mathematical analysis that explains the quite stunning performance of such a scheme for speckle imaging. Our analysis is based on the white-noise paraxial model, in which the wave amplitude is described by the Itô{Schrödinger equation. We identify a scaling regime where the scheme works well, which we refer to as the scintillation regime. In this regime the wavelength is smaller than the correlation radius of the medium, which in turn is smaller than the beam radius; moreover, the propagation distance is longest scale. The results presented in this paper conform with the sophisticated physical intuition that has motivated these schemes, but give a more detailed characterization of the performance. The analysis gives a description of (i) the information that can be extracted and with what resolution and (ii) the statistical stability or signal-to-noise ratio with which the information can be extracted. [ABSTRACT FROM AUTHOR]

Application of multiexposure speckle contrast imaging (MESI) methods for perfusion measurements can correct for the contribution of static scattering of the skin, at the expense of reduced temporal resolution as compared to classical single-exposure methods. Persistence of tissue scattering properties during the measurements could allow for an initial calibration and enhancement of the temporal resolution of the measurements. We aim to study the influence of the perfusion on the light scattering of the forearm skin and to use the obtained data for the enhancement of the temporal resolution. A wide range of skin perfusion states was induced while monitoring the changes in the dynamic range of the exposure-dependent contrast. Different measurement and evaluation methods were tested based on an initial MESI calibration followed by image recording with reduced number of exposure time values. The changes in the skin perfusion can alter not only the contribution of the static scattering to the speckle images but also the short-exposure time contrast limit. The perfusion-dependent scattering of the skin can invalidate the precalibrations (e.g., β calibration) characterizing the combination of the given tissue and the measurement system. [ABSTRACT FROM AUTHOR]

The aim of the study is to determine the influence of a partial temporary ischemia and reperfusion on the development of pancreatitis in laboratory rats. Material and Methods. The experiments were performed on 73 white rats. Occluded blood vessels and blood flow were recorded by digital biomicroscopy and laser speckle contrast imaging. Statistical data processing was carried out the program Statistica for Windows 6.0 using the Student's criterion. Results. Laser speckle imaging and digital microscopes provide the monitoring of blood flow in the vessels of the pancreas. After a five-minute partial ischemia reactive hyperemia occurs, changes are invertible. After a twenty-minute partial ischemic reactive hyperemia does not occur, without developing pancreatitis necrosis. Pancreas of alcoholized rats has been found out to be more sensitive to ischemia. Conclusion. The method of laser speckle imaging and intravital microscopy after digital five- and twenty-minute partial ischemia of the pancreas revealed phase opposite directed changes in its tissue perfusion and varying severity of postischemic pancreatitis.

The purpose: to establish influence of a full ischemia of different duration and the subsequent reperfusionon pathology development in pancreas of rats by means of laser speckle-visualization and lifetime digital microscopy. Materials and Methods. The work has been performed on 42 white rats of line Wistar in weight of 200-250 Research of properties of a blood-groove was made by means of methods laser Doppler flowmetry, digital biomicroscopy and a method of laser speckle-contrast visualization. Results. After the termination of a 5-minute full ischemia the speed of bloodflow has been increased in 2-3 times, clinic pancreatic necrosis is marked does not develop. After the termination of 20-minute full ischemia the increase in speed of a bloodflow did not occur, there were morphological and clinical signs of pancreatic necrosis. Conclusion, the efficiency of monitoring of microhemodynamics of pancreas in rats by the method of speckle-capillary of full field has been shown. Multidirectional phase of perfusion changes in pancreas have been revealed after reversible infringement of blood supply of different duration.

This research focuses on speckle noise suppression by changing the angle of divergence of the diffuser. Three types of diffuser designs are compared in the experiments. For all three types, the speckle contrast value is lower than 0.027, and the speckle phenomenon is invisible to the human eye. [ABSTRACT FROM AUTHOR]

We present a tunable output-frequency filter (TOF) algorithm to reconstruct the object from noisy experimental data under low-power partially coherent illumination, such as LED, when imaging through scattering media. In the iterative algorithm, we employ Gaussian functions with different filter windows at different stages of iteration process to reduce corruption from experimental noise to search for a global minimum in the reconstruction. In comparison with the conventional iterative phase retrieval algorithm, we demonstrate that the proposed TOF algorithm achieves consistent and reliable reconstruction in the presence of experimental noise. Moreover, the spatial resolution and distinctive features are retained in the reconstruction since the filter is applied only to the region outside the object. The feasibility of the proposed method is proved by experimental results. [ABSTRACT FROM AUTHOR]

It is demonstrated herein that the use of spatial Poincaré plots provides an efficient means to describe short and long-range correlations in the spatial structure of the measured intensity distribution of scattered coherent fields. The intensity distribution over a row of pixels in single frames of speckle fields with varying speckle sizes was considered. Statistical descriptors from the spatial Poincaré plots for these intensity data with variable lags were used to estimate the short and long-term variations in the measured intensities, and from these descriptors, the minimum speckle size in the speckle patterns was estimated. This approach yielded similar results for speckle size estimates as the more standard method of calculating the power spectral density of the intensity pattern and simultaneously provided information on the relative contributions of short-term and long-term variations in the measured intensity to the spatial structure of the scattered fields.

The blind structured illumination microscopy strategy proposed by Mudry et al. is fully re-founded in this paper, unveiling the central role of the sparsity of the illumination patterns in the mechanism that drives super-resolution in the method. A numerical analysis shows that the resolving power of the method can be further enhanced with optimized one-photon or two-photon speckle illuminations. A much improved numerical implementation is provided for the reconstruction problem under the image positivity constraint. This algorithm rests on a new preconditioned proximal iteration faster than existing solutions, paving the way to 3D and real-time 2D reconstruction. [ABSTRACT FROM PUBLISHER]

A new authentication method employing a laser and a scanner is proposed to improve image contrast of the finger vein and to extract blood flow pattern for liveness detection. A micromirror reflects a laser beam and performs a uniform raster scan. Transmissive vein images were obtained, and compared with those of an LED. Blood flow patterns were also obtained based on speckle images in perfusion and occlusion. Curvature ratios of the finger vein and blood flow intensities were found to be nearly constant, regardless of the vein size, which validated the high repeatability of this scheme for identity authentication with anti-spoofing. [ABSTRACT FROM AUTHOR]

Speckle imaging method is useful for monitoring of blood flow in living bodies. We have proposed so far the method for simultaneous imaging of blood flow and blood concentration change using laser speckle patterns at two wavelengths. However, our conventional measurement system has difficulty in adjusting the illuminating optical axis of two laser sources. Therefore, we introduce a novel arrangement using a coaxial fiber illumination in the detection of speckle patterns in two wavelengths. By this arrangement, the blood flow can be stably analyzed with a frame rate using an estimation parameter proposed by the authors based on the spatial contrast of speckle patterns. This parameter is useful for estimating an autonomic nervous function which reflects stress conditions caused by tension and excitement. In this study, we present measurements of the blood flow and blood concentration change in the fiber illumination, and its application to estimation of stress condition. [ABSTRACT FROM AUTHOR]

Digital Image Correlation (DIC) is a powerful technique which is used to correlate two image segments to determine the similarity between them. A correlation image is formed which gives a peak known as correlation peak. If the two image segments are identical the peak is known as auto-correlation peak otherwise it is known as cross correlation peak. The location of the peak in a correlation image gives the relative displacement between the two image segments. Use of DIC for in-plane displacement and deformation measurements in Electronic Speckle Photography (ESP) is well known. In ESP two speckle images are correlated using DIC and relative displacement is measured. We are presenting background review of ESP and disclosing a technique based on DIC for improved relative measurements which we regard as the improved DIC method. Simulation and experimental results reveal that the proposed improved-DIC method is superior to the conventional DIC method in two aspects, in resolution and in the availability of reference position in displacement measurements. [ABSTRACT FROM AUTHOR]

Seed imbibition is a very important process in plant biology by which, thanks to a simple water income, a dry seed may turn into a developing organism. In natural conditions, this process occurs in the soil, e.g., with difficult access for a direct observation. Monitoring the seed imbibition with non-invasive imaging techniques is therefore an important and possibly challenging task if one tries to perform it in natural conditions. In this report, we describe a set of four different imaging techniques that enable to addressing this task either in 3D or in 2D. For each technique, the following items are proposed. A detailed experimental protocol is provided to acquire images of the imbibition process. With the illustration of real data, the significance of the physical quantities measured in terms of their relation to the income of water in the seed is presented. Complete image analysis pipelines are then proposed to extract dynamic information on the imbibition process from such monitoring experiments. A final discussion compares the advantages and current limitations of each technique in addition to elements concerning the associated throughput and cost. These are criteria especially relevant in the field of plant phenotyping where large populations of plants are imaged to produce quantitatively significative traits after image processing.

Fringe orientation and density are important properties of fringes. The estimation of fringe orientation and density from electronic speckle pattern interferometry (ESPI) fringe patterns with greatly variable density is still a challenging problem faced in this area. We propose an effective method based on variational image decomposition to estimate fringe orientation and density simultaneously. The BL – Hilbert model is proposed to successfully decompose an ESPI fringe pattern with greatly variable density into two images: one only includes low density fringes and the other high density fringes. The density of the two decomposed images are uniform. We estimate the orientation and density of the two decomposed images by existing methods. The whole fringe orientation and density can be obtained by combining the corresponding results of the two decomposed images. We evaluate the performance of our method via application to the computer-simulated and experimentally obtained ESPI fringe patterns with greatly variable density and comparison with the widely used three methods. [ABSTRACT FROM AUTHOR]

Imaging systems targeting macroscopic objects tend to have poor depth selectivity. In this Letter, we present a 3D imaging system featuring a depth resolution of 200 µm, depth scanning range of more than 1 m, and view field larger than 70×70 mm 2 . For depth selectivity, we set up an off-axis digital holographic imaging system using a light source with a coherence length of 400 µm. A prism pair was installed in the reference beam path for long-range depth scanning. We performed imaging macroscopic targets with multiple different layers and also demonstrated imaging targets hidden behind a scattering layer. [ABSTRACT FROM AUTHOR]

The statistical properties of speckle relevant to short- to medium-range (tactical) active tracking involving polychromatic illumination are investigated. A numerical model is developed to allow rapid simulation of speckled images including the speckle contrast reduction effects of illuminator bandwidth, surface slope, and roughness, and the polarization properties of both the source and the reflection. Regarding surface slope (relative orientation of the surface normal and illumination/observation directions), Huntley's theory for speckle contrast, which employs geometrical approximations to decrease computation time, is modified to increase accuracy by incorporation of a geometrical correction factor and better treatment of roughness and polarization. The resulting model shows excellent agreement with more exact theory over a wide range. An experiment is conducted to validate both the numerical model developed here and existing theory. A diode laser source with coherence length of 259 ± 7 µm is reflected off of a silver-coated diffuse surface. Speckle data are gathered for 16 surface slope angles corresponding to speckle contrast between about 0.55 and 1. Taking the measured data as truth, both equations show error mean and standard deviation of less than 3%. Thus, the theory is validated over the range of this experiment. [ABSTRACT FROM AUTHOR]

Defocused speckle imaging (DSI) is an optical technique where a diffuse object surface is illuminated by a laser source, and the scattered interference speckle field is sampled by a defocused camera. The recorded image contains a speckle pattern that characterizes the surface; if the object displaces or rotates, the speckles move within the camera view. Non-contact surface motion measurements are thus possible by simply tracking the speckle movements. The observed speckle motion magnitude scales proportional to the object distance, which makes DSI attractive for remote measurement applications. However, because DSI measurement sensitivity depends on the specific geometric arrangement, object range and orientation must be known to properly scale the measured speckle motions. In field conditions, manual extraction of the geometric parameters is challenging and time-consuming due to large distances and harsh conditions. To solve the scaling problem, a diffraction-based self-calibration method is proposed here to extract the geometric parameters from the captured speckle patterns directly with no additional sensors. The solution utilizes multi-longitudinal mode laser illumination combined with speckle pattern diffraction analysis. A laser with a multi-wavelength spectrum creates several copies of partially overlapping speckle patterns that propagate at slightly different directions. The related spatial speckle offset measured on the image sensor depends on the surface angle and scales proportional to the sampling distance. Therefore, all calibration parameters can be explicitly determined from a pair of speckle patterns recorded at axially separated focal planes. The speckle offset equations are derived from the general diffraction equation using simple geometric treatment. The speckle pattern dependence on the laser source spectrum is experimentally studied, and the proposed self-calibration method is demonstrated. The diffraction analysis can extract 500–1000 mm sampling distances at a 1.7% accuracy and determine 15–45˚ oblique surface angles at a 0.7˚ accuracy. [ABSTRACT FROM AUTHOR]

Phase-contrast X-ray imaging using a paper analyzer enables the visualization of X-ray transparent biological structures using the refractive properties of the sample. The technique measures the sample-induced distortions of a spatially random reference pattern to retrieve quantitative sample information. This phase-contrast method is promising for biomedical application due to both a simple experimental set-up and a capability for real-time imaging. The authors explore the experimental configuration required to achieve robustness and accuracy in terms of (i) the paper analyzer feature size, (ii) the sample-to-detector distance, and (iii) the exposure time. Results using a synchrotron source confirm that the technique achieves accurate phase retrieval with a range of paper analyzers and at exposures as short as 0.5 ms. These exposure times are sufficiently short relative to characteristic physiological timescales to enable real-time dynamic imaging of living samples. A theoretical guide to the choice of sample-to-detector distance is also derived. While the measurements are specific to the set-up, these guidelines, the example speckle images, the strategies for analysis in the presence of noise and the experimental considerations and discussion will be of value to those who wish to use the speckle-tracking paper analyzer technique. [ABSTRACT FROM AUTHOR]

The presented paper deals with the data processing of correlograms acquired by an electronic speckle pattern interferometry (ESPI). Correlograms are highly noised by the speckle pattern and special care should be taken to denoise these correlograms before calculating the demanded phase map or phase profile. This paper presents a process that utilizes two stage use of wavelet transform (WT) for both denoising and a phase profile retrieval. In the first stage the correlogram is denoised by thresholding of wavelet transform coefficients. Unlike the common use, WT phase retrieval process is not directly applied to the denoised correlogram, but rather to its intensity thresholded image, which is done in the second stage. Proposed algorithm is verified by its application to the artificially generated correlograms and in the final step also to the experimentally acquired correlograms. [ABSTRACT FROM AUTHOR]

Laser speckle technique is a useful means for imaging blood flow in living bodies and, it has been utilized for analyzing the condition of living bodies or the health state. However, depth of a blood flow region has not been measured yet by this method. In the present study, we investigate use of a decorrelation in a pair of speckle patterns in a temporal sequence for measuring depth of the blood flow region. Blood flow is also measured simultaneously by means of a spatio-temporal difference of the same pair of speckle patterns as that used for depth measurement. Experiments are conducted for reference and sample models using ground-glass plates and a silicone layer and for a human finger, to confirm the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

One way to restore scattered optical imaging is retrieving its phase through the speckle autocorrelation. However, the commonly used methods have the disadvantages such as poor recovery quality, the need to select the initial value multiple times and insufficient noise immunity. A method named imaging through scattering layers by exploiting the sum of gradient amplitude guided phase retrieval is proposed in this paper. Sparsity enhancement operation is added to the solution obtained in each iteration and a value called the sum of gradient amplitudes is used to control the number of iterations. This method can effectively improve the quality of restored images. It can also effectively recover the object with any initial iteration value and have better noise resistance by a specific designed parameter in the iteration. • An algorithm called the sum of gradient amplitude guided phase retrieval is proposed in this paper. • A sparsity enhancement step is added in the phase retrieved algorithm to decrease the times of selecting initial values. • The concept of the sum of the Fourier transform amplitude of the gradient is designed as the error criterion and the controller of number of iterations. • A parameter is introduced to control step size in the iteration process, which can improve the noise resistance of the algorithm. [ABSTRACT FROM AUTHOR]

In imaging of blood flow by means of a laser speckle technique, we have proposed so far an estimation parameter based on the spatial contrast of speckle patterns observed for the blood flow in skin tissue and a blood vessel. This parameter enable us to image a relative blood flow distribution from a single speckle pattern, thus, it analyzes the blood flow with a frame-rate of an imaging device used. In this study, we investigated availability of this parameter for detecting changes in arterial blood flow caused by medication and cold stimulation to the skin tissue. Experiments were conducted for an anesthetized rat and a human wrist to confirm the feasibility of the present parameter. [ABSTRACT FROM AUTHOR]

The potential benefits of real-time, or near-real-time, image processing hardware to correct for turbulence-induced image defects for long-range surveillance and weapons targeting are sufficient to motivate significant resource commitment to their development. Quantitative comparisons between potential candidates are necessary to decide on a preferred processing algorithm. We begin by comparing the mean-square-error (MSE) performance of speckle imaging (SI) methods and multiframe blind deconvolution (MFBD), applied to long-path horizontal imaging of a static scene under anisoplanatic seeing conditions. Both methods are used to reconstruct a scene from three sets of 1000 simulated images featuring low, moderate, and severe turbulence-induced aberrations. The comparison shows that SI techniques can reduce the MSE up to 47%, using 15 input frames under daytime conditions. The MFBD method provides up to 40% improvement in MSE under the same conditions. The performance comparison is repeated under three diminishing light conditions, 30, 15, 8 photons per pixel on average, where improvements of up to 39% can be achieved using SI methods with 25 input frames, and up to 38% for the MFBD method using 150 input frames. The MFBD estimator is applied to three sets of field data and representative results presented. Finally, the performance of a hybrid bispectrum-MFBD estimator that uses a rapid bispectrum estimate as the starting point for the MFBD image reconstruction algorithm is examined. [ABSTRACT FROM AUTHOR]