Speckle Photography Research Articles

Comparison of Feature Histograms and Co-occurrence Matrix on Analysis of the Light Spectrum Effect for Identification of Surface Roughness with Speckle Images

Abstract Speckle imaging is a technique that can be used for digital image analysis. Speckle imaging technology essentially uses a laser to create a pattern of dots through the laser’s interference with an object. The advantage of speckle photography is that it is safe and does not require direct contact with the subject. In this study, speckle imaging techniques were used to analyze the surface roughness of objects. Speckle imaging techniques are used to investigate the influence of the choice of laser spectrum on the determination of the surface roughness of an object. For objects with rough surfaces, it comes in 80 sheets of coarse sandpaper and 2000 sheets of fine sandpaper. This study aims to compare the accuracy of identification results using Histogram Features and Co-occurrence Matrix Features when analyzing the influence of laser wavelength on object spot image identification. The research procedures included identifying rough objects, collecting point image data on rough surfaces using a series of experiments, pre-processing the point images, extracting features using histograms and co-occurrence matrices, and using a naive Bayes classifier. It includes determining surface roughness and performing comparisons between them. The resulting feature histogram and feature appearance matrix. This study shows that the use of Histogram Features and coexistence matrix features yields similar conclusions regarding the influence of the laser beam spectrum in determining the surface roughness of an object. The difference between Histogram Features and Co-occurrence Matrix Features lies in the pattern of detection results. Differences in the detection result patterns may be caused by differences in the characteristics of the Histogram Features and Co-occurrence Matrix Features of each speckle image used in the study. Although the detection result patterns of the Histogram Feature amount and the Co-occurrence Matrix feature amount are different, the accuracy of the detection result is equivalent. The similarity in the accuracy of the detection results may be caused by the similarity in the effectiveness of the two features in detecting the speckle image pattern.

Quality evaluation of eggs during shelf-life ambient storage by laser speckle technique

Laser speckle technique is non-destructive, cost-effective with a simple experimental setup, and has been used in the field of agriculture, food processing, medicines etc. A coherent laser source, CCD Camera, and a recording system are needed to record the speckle image. Our objective of this work is to both quantify and visualize the quality of chicken eggs using the non-destructive Laser speckle technique and also to verify the outcomes with other established destructive techniques such as calculation of Haugh Unit (HU), Yolk Index (YI), PH value etc. In this work, we have done the single exposure speckle image as well as the biospeckle activity analysis of eggs stored under ambient conditions at room temperature (29±3°C) for seven days of shelf-life storage. We have approached a new probabilistic method to quantify a single exposure speckle image and the Frequent Motion Image (FMI) method to construct the speckle activity map of the egg's internal constituents. As a result, we have found that the biospeckle activity of eggs decreased by 24–38% after seven days, its internal activity map changed significantly. An egg on the first day of storage shows high biospeckle activity compared to other days. For the single exposure speckle image, the calculated Average energy decreased by 40–60%, and Entropy increased by 10–15%, with significant differences for each day during seven days of shelf storage. The average HU decreases by around 15%, and the YI decreases by 10% during seven days of ambient storage.

Combining transmission speckle photography and convolutional neural network for determination of fat content in cow milk: an exercise in classification of parameters of a complex suspension

Combining transmission speckle photography and convolutional neural network for determination of fat content in cow milk: an exercise in classification of parameters of a complex suspension

Dynamic laser speckle study on the effect of TiO2 and SiO2 nanoparticles in coatings

The coatings of TiO2 and SiO2 nanoparticles mixed with latex paint on the sample are studied. The sample coin is coated primarily with latex paint alone and then with additives such as TiO2 and SiO2 nanoparticles separately with the same percentage of concentration. The sample is illumined by a coherent source of light and produces tiny bright and dark fingerprints by the interference effect of the scattered laser. This cigar-like granular pattern image is known as a speckle pattern which is recorded continuously during the drying process of paint. The modified properties due to the additives in paint on the coin are studied by speckle photography. The surface profile plotting method is adopted for the roughness analysis on the sample. Histogram and gray level co-occurrence matrix perform the intensity analysis in the paint. The brightness examine by means of bright/dark pixel counting method.

Effect of heat treatment on deformation inhomogeneity of carbon steel / stainless steel bimetal

The work is devoted to the study of the effect of annealing on mechanical properties and inhomogeneity of plastic deformation of a bimetallic plate made of stainless / carbon steel with the dimensions of the working part 50×7×2 mm. To develop laser technology for producing bimetals of various compositions, the contact zone of two dissimilar steels is of greatest interest. Since the performance characteristics of the entire product as a whole depend on the structure and properties of this zone, interaction of the components of the bimetal in the process of its manufacture leads to appearance of heterogeneity of various types near the interface and in the volumes adjacent to it. The research material was obtained by laser cladding of wire AISI 304 stainless steel on a plate of low-carbon steel St3. Bimetallic samples were subjected to vacuum heating at a temperature of 700 °C at various times from 2 to 8 h. The use of data on the distributions of local strains by the speckle photography method made it possible to consider the process of plastic flow in the initial section of tension diagram and to establish the effect of annealing temperature on plastic strain localization during mechanical tests. For a quantitative assessment of deformation inhomogeneity in the main and cladding layers, we used spatiotemporal distributions of local elongations and the corresponding values of the variation coefficient. It was established that the level of deformation inhomogeneity of microvolumes at the interface during tension is higher than that of the bimetal main layers. With increase in the annealing time, increase in the variation coefficient in the joint zone is noted, which is more significant on the stainless steel side, and this increases the probability of microcracks initiation. The increased level of deformation inhomogeneity of microvolumes of the cladding layer carburized zone is contingent on the increased localization of deformation in nearby microvolumes due to structural heterogeneity.

Design and validation of a convolutional neural network for fast, model-free blood flow imaging with multiple exposure speckle imaging.

Multiple exposure speckle imaging has demonstrated its improved accuracy compared to single exposure speckle imaging for relative quantitation of blood flow in vivo. However, the calculation of blood flow maps relies on a pixelwise non-linear fit of a multi-parametric model to the speckle contrasts. This approach has two major drawbacks. First, it is computer-intensive and prevents real time imaging and, second, the mathematical model is not universal and should in principle be adapted to the type of blood vessels. We evaluated a model-free machine learning approach based on a convolutional neural network as an alternative to the non-linear fit approach. A network was designed and trained with annotated speckle contrast data from microfluidic experiments. The neural network performances are then compared to the non-linear fit approach applied to in vitro and in vivo data. The study demonstrates the potential of convolutional networks to provide relative blood flow maps from multiple exposure speckle data in real time.

Speckle photography and double aperture speckle interferometry using both sides of a suitably designed hololens imaging configuration

In the present work, both sides of a suitably designed hololens imaging configuration have been used in laser speckle photography and double aperture speckle interferometry. A speckle photographic technique has been used to measure in-plane displacement, and a double aperture speckle interferometric technique has been used to measure in-plane displacement component.

Macroscopic Spatio-Temporal Patterns of Localized Plastic Flow Development under Tension of Fe-Cr-Ni Alloys

This study examines the patterns of macroscopic inhomogeneity and localization of plastic flow in Fe-Cr-Ni polycrystals subjected to uniaxial tension. By varying the test temperature, the deformation curves can be altered, allowing us to explore the behavior of the material under different conditions. The stress-strain diagrams obtained from the samples reveal the areas of elastic deformation, plastic flow, and fracture. To experimentally study plastic flow, we used speckle photography to accurately reconstruct the displacement vector fields and calculate the components of the plastic distortion tensor. The results showed that plastic flow is localized at all stages of the process for test temperatures of+65, +24, and -60 °C. The forms oflocalization are entirely determined by the dependence of the strain hardening coefficient on the deformation during the relevant stage of the process. An analysis of the spatial distributions of local shifts and local rotations was conducted. We observed spatially periodic structures that can be interpreted as autowave processes and explained in terms of the concept of self-organization of the plastic flow process.

An efficient optical diffuser fabricated from fungal mycelium

Scattering of light from randomly textured materials is ubiquitous and of great interest in biology and for diverse applications—including filtering, light trapping in solar cells, and speckle photography. One attractive means to build these materials is by harnessing the complexity present in structures of biological origin. Here, we report on the development of a random phase diffuser based on intertwined filamentous cells (hyphae) of the fungus Trichoderma atroviride. A fungal colony (mycelium) is grown on the surface of a gel medium, and then removed, fixated, and dehydrated, resulting in a free-standing, two-dimensional random mesh (1 cm × 1 cm × 5 μm) composed of rigid hyphae separated by air gaps. A laser beam incident on the bioplate results in speckle patterns of nearly equal intensity in transmission and reflection. By modeling the bioplate as composed of optical phase elements and computing Fraunhofer diffraction, we recover the overall shape of the observed diffuse light spot. As the hyphal density composing the sample is increased, all optical power is in the speckle pattern, and approximate Lambertian transmissivity is reached. Altogether, our observations suggest that a planar fungal colony can scatter light efficiently by imparting a random phase. These results underscore the potential of a biological structure to develop optical elements and to use light scattering to evaluate morphology in complex structures—such as filamentous mycelia.

Пластическое течение в твердых растворах Cu-Ni как автоволновой процесс

The influence of Ni content in Cu-Ni alloys on the localization of plastic flow under uniaxial tension has been studied. The regularities of localization of plastic deformation during linear and parabolic deformation hardening, as well as at the yield point, depending on the Ni content in the solid solution, have been studied by the speckle photography method. The influence of the Ni content on the duration of the stages of parabolic deformation hardening in alloys of different composition was found. The dependence of the spatial period of localization of plastic deformation (the length of the localization autowave) on the Ni content in the studied alloys is established. Keywords: localization of plastic deformation, autowaves, copper-nickel alloys, structure, mechanical properties, deformation and impurity hardening.

Evaluation of the difference in multilayer thickness of TiO2 thin film by laser speckle photography

TiO2 thin film thickness is measured after each layer of coatings by laser speckle photography. TiO2 thin film coatings are carried out on the steel substrate in a periodical way by the spin coating method. At the time t1, the first layer coating scatters the coherent laser and develops the self-interference pattern of an image called speckle, which is captured and auto-correlated. After time t2, the speckle image is recorded by CCD and cross-correlated with the previous one. There is pixel distance movement and it is computed by image processing. This speckle imaging practice gives 8 µm as the thickness of the second layer of Tio2 film coating. Hence, the shift of pixel distance gives the thickness of the multilayer sample coatings in a satisfactory manner.

In-process measurement of mechanical loads during electrical discharge machining

In electrical discharge machining, in-process measurements of the induced mechanical stress are essential to develop process models for improving the fatigue strength of the machined part. For this purpose, high-speed digital speckle photography is introduced to measure the workpiece-side load fields with a lateral displacement resolution of 28 nm at a spatiotemporal resolution of 29 µm and 40 µs, respectively. As a result, the load effects of even individual 100 µs short discharge pulses are temporally resolved for the first time, and the occurring spatial load inhomogeneities and their dynamics are characterized to complement our understanding of the machining process.

Digital speckle photography in the presence of displacement gradients

Digital speckle photography is a displacement field measurement method that employs laser speckles as surface markers. Since the approach requires only one reference image without a preparation of the sample and provides a fast, single-shot measurement with interferometric precision, the method is applied for in-process measurements in manufacturing engineering. Due to highly localized loads, higher-order displacement gradients occur in manufacturing processes and it is an open research question how these gradients affect the measurement errors of digital speckle photography. We simulate isotropic Gaussian surface topographies, apply a displacement field and then generate laser speckle patterns, which are evaluated with digital image correlation and subsequently the resulting random and systematic errors of the displacement field are analyzed. We found that the random error is proportional to the first-order displacement gradient and results from decorrelation of the laser speckles. The systematic error is mainly caused by the evaluation algorithm and is linearly dependent on the second-order gradient and the subset size. We evaluated in-process displacement measurements of laser hardening, grinding and single-tooth milling where we determined the relative error caused by displacement gradients to be below 2.5% based on the findings from the simulative study.

Plastic flow in Cu-Ni solid solutions as an autowave process

The influence of Ni content in Cu-Ni alloys on the localization of plastic flow under uniaxial tension has been studied. The regularities of localization of plastic deformation during linear and parabolic deformation hardening, as well as at the yield point, depending on the Ni content in the solid solution, have been studied by the speckle photography method. The influence of the Ni content on the duration of the stages of parabolic deformation hardening in alloys of different composition was found. The dependence of the spatial period of localization of plastic deformation (the length of the localization autowave) on the Ni content in the studied alloys is established. Keywords: localization of plastic deformation, autowaves, copper-nickel alloys, structure, mechanical properties, deformation and impurity hardening.

Optically rough TiO2 thin film surface study by laser speckle photography

In this work, TiO2 thin film is exposed to the red laser and the scattered light progresses the self-interference granular appearance of images called speckle patterns. The statistical database of the scattered fingerprints of the object is computed. The speckle images are captured by a Charge Coupled Device(CCD) and are then explored by digital speckle processing to acquire the surface roughness. This technique is appropriate to determine the average optical roughness(Ra) of the specimen and the sub-micron range of Root Mean Square(RMS) values of the sample agreed well by way of the stylus conventional profilometer method.

Study of deformation structures maps in metals under tension

The paper considers the regularities of macroscopic inhomogeneity of plastic flow during uniaxial tension of flat samples of Fe-Cr-Ni 2 mm thick. Their tension axis was oriented along the rolling direction. The average grain size was 12.5 ± 3 mm. The plastic flow curves of the alloy had long stages of linear strain hardening over the entire test temperature range 180 K < T < 297 K. For the experimental study of plastic deformation, we used the method of accurately reconstructing the fields of displacement vectors and calculating the components of the plastic distortion tensor using speckle photography with increments of the total strain between exposures 0.001. The field of displacement vectors as a whole over the sample during loading is inhomogeneous both in the directions of the displacement vectors and in values; in some areas, the displacement vectors nonmonotonically change directions relative to the tension axis. It has been established that in the test temperature range 180 K < T < 297 K, plastic flow is localized at all stages of the process. The appearance of the a′-martensite phase during the deformation of the alloy under study leads to a change in the mechanical characteristics, the work hardening coefficient, and the deformation localization parameters. The maps of deformation structures are analyzed in the form of spatial distributions of the components of the plastic distortion tensor: local elongations, narrowings, shifts and rotations. The non-linear nature of the change in the coefficient of transverse deformation from the level of acting stresses is established. The general form and quantitative parameters of the evolution of the components of the plastic distortion tensor indicate the connection of this process with the self-organization of a defective subsystem in a deformable medium.

Inter-day repeatability assessment of human retinal blood flow using clinical laser speckle contrast imaging.

Laser speckle contrast imaging (LSCI) can generate retinal blood flow maps inexpensively and non-invasively. These flow maps can be used to identify various eye disorders associated with reduced blood flow. Despite early success, one of the major obstacles to clinical adoption of LSCI is poor repeatability of the modality. Here, we propose an LSCI registration pipeline that registers contrast maps to correct for rigid movements. Post-registration, intra(same)-day and inter(next)-day repeatability are studied using various quantitative metrics. We have studied LSCI repeatability intra-day by using the coefficient of variation. Using the processing pipelines and custom hardware developed, similar repeatability was observed when compared to previously reported values in the literature. Inter-day repeatability analysis indicates no statistical evidence (p = 0.09) of a difference between flow measurements performed on two independent days. Further improvements to hardware, environmental controls, and participant control must be made to provide higher confidence in the repeatability of blood flow. However, this is the first time that repeatability across two different days (inter-day) using multiple exposure speckle imaging (MESI) has been analyzed and reported.

EVALUATION OF THE APPLICATION OF DOUBLE-EXPOSURE SPECKLE PHOTOGRAPHY WITH DIFFERENT APERTURES IN EXPERIMENTAL MECHANICS

The article presents an experimental evaluation of the use of double-exposure speckle photography with circular and annular apertures in experimental mechanics using the example of determining the modulus of elasticity in tension. The description of the process of registration of speckle photography and its subsequent processing is given. Based on the results of calculations of the finite element model of the sample, the areawhere the boundary conditions do not affect its tension is determined. A description is given of the procedure for processing speckle photographs to determine the modulus of elasticity and the error in its measurement with different apertures.

Interior Deformation and Failure of a Short Composite Sandwich Beam under Three-Point Bending

Composite sandwich plates and beams are increasingly employed as an engineering material in structures such as airplanes, ships, bridges, and vehicles because of their superb strength to weight ratio. Understanding a sandwich structure’s failure mechanism is a prerequisite for a safety design. In this paper, we employ a new experimental technique called DVSP (Digital Volumetric Speckle Photography) to map the interior deformation of a short composite sandwich beam under three-point bending. 3D displacement fields and shear strain fields of 5 transverse and 4 longitudinal sections of the beam are mapped quantitatively in detail as a function of increasing load. The beam fails in delamination of the interface between the face sheet and core.

Laser speckle image velocimetry by Fast Fourier Transform technique

In this paper, laser image velocimetry, a unique optical method for the velocity measurement of fluid flow has been validated. A laser sheet is illuminated on microscopic seeded particles to produce the speckle pattern at the recording plane. Double frame-single exposure speckle images are captured in such a way that the second speckle image is shifted exactly in a known direction. The auto-correlation method has an ambiguity to identify the direction of flow. To sort out this problem, the partial shift of the second image has been premeditated. Cross-correlation of sub interrogation areas of the speckle patterns is attained by the Fast Fourier Transform technique. Segmented four sub-windows are processed to acquire the velocity information with a vector map precisely.