Shadow Images Research Articles

Soft shadow images

In traditional optics education, shadows are often regarded as a mere triviality, namely as silhouettes of obstacles to the propagation of light. However, by examining a series of shadow phenomena from an embedded perspective, we challenge this view and demonstrate how in general both the shape of the object and light source have significant impact on the resulting soft shadow images. Through experimental and mathematical analysis of the imaging properties of inverse objects, we develop a generalized concept of shadow images as complementary phenomena. Shadow images are instructive examples of optical convolution and provide an opportunity to learn about the power of embedded perspective for the study of optical phenomena in the classroom. Additionally, we introduce the less-known phenomenon of the bright shadow.

Shadow removal method of soil surface image based on GAN used for estimation of farmland soil moisture content

It is important to obtain soil moisture content (SMC) in farmland, and soil surface images can be used to rapidly estimate SMC. The objective of this study was to propose a shadow removal algorithm to eliminate the effect of shadows in soil surface images, so as to improve the accuracy of SMC estimation. The structure of the proposed soil shadow generative adversarial networks (SS GAN) was a circulating network, which is an unsupervised method and does not require paired shadow image sets for network training. Four loss functions were defined for the network to effectively remove shadows and ensure texture detail and color consistency. This method is compared with traditional methods, supervised and unsupervised deep learning techniques by comparative experiments. Evaluations were made from visual and quantitative comparisons. Visually, the best shadow removal method was proved, it almost has no shadow boundaries or shadow areas visible for samples. The peak signal to noise ratio (PSNR) and structural similarity (SSIM) were used to quantitatively compare shadow removal images with real non-shadow images. The PSNR and SSIM of SS GAN were 28.46 and 0.95 respectively, which are superior to other methods, indicating that the images processed by SS GAN were closer to the real non-shadow images. Field experiments results shown that SS GAN has excellent shadow removal performance in the self-developed vehicle-mounted detection system. In order to verify the improvement effect of shadow removal image on SMC estimation accuracy, further field test was conducted to estimate SMC. Compared with SMC estimation results before and after shadow removal, R 2 increased from 0.69 to 0.76, and root mean square error decreased from 1.39 to 0.94%. The results show that the proposed method can effectively remove the shadow of soil image and improve the accuracy of SMC estimation in farmland.

Comparison between shadow imaging and in-line holography for measuring droplet size distributions

A direct comparison of the droplet size and number measurements using in-line holography and shadow imaging is presented in three dynamically evolving laboratory scale experiments. The two experimental techniques and image processing algorithms used to measure droplet number and radii are described in detail. Droplet radii as low as r = 14 µm are measured using in-line holography and r = 50 µm using shadow imaging. The droplet radius measurement error is estimated using a calibration target (reticle) and it was found that the holographic technique is able to measure droplet radii more accurately than shadow imaging for droplets with r le 625 µm. Using the measurements of droplet number and size we quantitatively cross-validate and assess the accuracy of the two measurement techniques. The droplet size distributions, N(r), are measured in all three experiments and are found to agree well between the two measurement techniques. In one of the laboratory experiments, simultaneous measurements of droplets (r ge 14 µm, using holography) and dry aerosols (0.07 lessapprox r lessapprox 2 µm, using an scanning mobility particle sizer and 0.15 lessapprox r lessapprox 5 µm using an optical particle sizer) are reported, one of the first such comparison to the best of our knowledge. The total number and volume of droplets is found to agree well between both techniques in the three experiments. We demonstrate that a relatively simple shadow imaging technique can be just as reliable when compared to a more sophisticated holographic measurement technique over their common droplet radius measurement range. The agreement in results is shown to be valid over a large range of droplet concentrations, which include experiments with relatively sparse droplet concentrations as low as 0.02 droplets per image. Advantages and disadvantages for the two techniques are discussed in the context of our results. The main advantages to in-line holography are the greater accuracy in droplet radius measurement, greater spatial resolution, larger depth of field, and the high repetition rate and short pulse duration of the laser light source. In comparison, the main advantages to shadow imaging are the simpler experimental setup, image processing algorithm, and fewer computer resources necessary for image processing. Droplet statistics like number and size are found to be very reliable between the two methods for large range of droplet densities, {mathcal {P}}_{r>50}, ranging from 10^{-4} le {mathcal {P}}_{r>50} le 10^{-1} cm^{-3}, when the two techniques are implemented as shown in this paper.

A secure and effective image encryption scheme by combining parallel compressed sensing with secret sharing scheme

In the complex network environment, it is becoming more and more significant to protect the security of information during transmission. A secure and effective image encryption scheme by combining parallel compressed sensing with secret sharing scheme is presented in this paper. Firstly, an image is measured by parallel compressed sensing, which not only realizes compression and encryption in the meantime, but also reduces computational complexity and storage space, and enhances transmission efficiency. Secondly, a block Arnold transformation is applied to process the measurement value image, and the obtained image is called a secret image, so as to achieve the effects of scrambling and encryption. Then, the secret image is partitioned into n shadow images by Shamir’s (t,n)-threshold secret sharing scheme, at least any t of n shadows images are able to recover the secret image, so the size of shadow images can be adjusted according to different application scenarios, which is flexible. This method realizes the encryption effect, and enhances the security of the secret image. Finally, to ensure the security of shadow images, the Zigzag confusion is introduced to process n shadow images and realizes the encryption effect. Experimental results manifest that our scheme realizes security and availability of the network system under the condition of limited resources.

Exploration of Chinese cultural communication mode based on the Internet of Things and mobile multimedia technology.

Image retrieval technology has emerged as a popular research area of China's development of cultural digital image dissemination and creative creation with the growth of the Internet and the digital information age. This study uses the shadow image in Shaanxi culture as the research object, suggests a shadow image retrieval model based on CBAM-ResNet50, and implements it in the IoT system to achieve more effective deep-level cultural information retrieval. First, ResNet50 is paired with an attention mechanism to enhance the network's capacity to extract sophisticated semantic characteristics. The second step is configuring the IoT system's picture acquisition, processing, and output modules. The image processing module incorporates the CBAM-ResNet50 network to provide intelligent and effective shadow play picture retrieval. The experiment results show that shadow plays on GPU can retrieve images at a millisecond level. Both the first image and the first six photographs may be accurately retrieved, with a retrieval accuracy of 92.5 percent for the first image. This effectively communicates Chinese culture and makes it possible to retrieve detailed shadow-play images.

A plasma self-confinement method induced by mutual extrusion of shock waves for liquid analysis of LIBS

To overcome the problems of poor plasma stability and low measurement repeatability caused by fluctuation and sputtering of liquid, a method called plasma self-confinement is proposed for liquid measurement by laser-induced breakdown spectroscopy (LIBS) in this work. With the help of shadow images, it was found that the liquid target could be returned to a calm state in a very short time, and the plasma back shock wave could be suppressed effectively. A quantitative analysis of the sodium chromate solution showed that the self-absorption could be reduced and the repeatability and sensitivity could be improved by plasma self-confinement mode LIBS when compared with liquid sheet mode LIBS.

Comparative study of evolution of structured flows at boundary of the regime change “diffusion — concentration convection” in isothermal multicomponent mixing in gases by techniques of visual and numerical analysis

During isothermal multicomponent diffusion process, the number of effects appear that are not observed visually when mixed in binary mixtures. These include occurrence of convective instability with subsequent formation of structured flows. The feature of this type of mixing is that convection is realized under conditions of decrease in density of mixture with height. Flow visualization method allows to fix information about distribution of medium parameters by dynamics of structures in convective flows. Application of computer processing methods, as well as techniques of identifying images of thermophysical fields, allows to obtain quantitative information about convective flows. For an isothermal ternary gas mixture heliumargonnitrogen, shadow images of structural formations formed in convective flows due to the instability of mechanical equilibrium are represented in this work. To carry out digital analysis of experimental shadow images, a simplified virtual model of the lower chamber of the diffusion cell was created. Based on digital analysis of visual images, quantitative characteristics related to estimation of the size of convective formations, period of their formation, and linear velocity of convection cells when moving through diffusion channel are presented. It has been established that the growing convective disturbances arising in the system cause a change in the characteristic scale of convective cells. The analysis of shadow images also showed that a vortex is formed in convective flows, which consists mainly of a component with the highest molecular weight. Comparison of visual images of experimental fields with simulation flows is implemented, on the basis of which composition of mixture components in convective structures is estimated. It is shown that the obtained value of the concentration of the heavy component in the vortex filament can be taken as the minimum.

Reversible extended secret image sharing with ability to correct errors based on Chinese remainder theorem

The reversible extended secret image sharing (RESIS) scheme can safely segment the secret image into a shadow image and embed it into the cover image, while ensuring that both the secret image and the cover image are completely restored. The existing schemes do not consider the attack on the information transmission channel, and often cannot correctly recover the secret image when attacked. In view of this, this paper fully considers the active attack on the information channel, and then proposes a RESIS scheme with error correction capability. In this paper, the Reed-Solomon code is used to detect modification attacks and correct errors to a certain extent. Additionally, the lossless recovery effect of both the secret image and the cover image is accomplished in conjunction with secret sharing scheme based on the Chinese remainder theorem. According to experimental findings, this method can resist certain active attacks.

Testing symmergent gravity through the shadow image and weak field photon deflection by a rotating black hole using the M87^* and Sgr. hbox {A}^* results

In this paper, we study rotating black holes in symmergent gravity, and use deviations from the Kerr black hole to constrain the parameters of the symmergent gravity. Symmergent gravity induces the gravitational constant G and quadratic curvature coefficient c_{textrm{O}} from the flat spacetime matter loops. In the limit in which all fields are degenerate in mass, the vacuum energy V_{textrm{O}} can be wholly expressed in terms of G and c_{textrm{O}}. We parametrize deviation from this degenerate limit by a parameter {hat{alpha }} such that the black hole spacetime is dS for {hat{alpha }} < 1 and AdS for {hat{alpha }} > 1. In constraining the symmergent parameters c_{textrm{O}} and {hat{alpha }}, we utilize the EHT observations on the M87* and Sgr. A* black holes. We investigate first the modifications in the photon sphere and shadow size, and find significant deviations in the photonsphere radius and the shadow radius with respect to the Kerr solution. We also find that the geodesics of time-like particles are more sensitive to symmergent gravity effects than the null geodesics. Finally, we analyze the weak field limit of the deflection angle, where we use the Gauss-Bonnet theorem for taking into account the finite distance of the source and the receiver to the lensing object. Remarkably, the distance of the receiver (or source) from the lensing object greatly influences the deflection angle. Moreover, c_{textrm{O}} needs be negative for a consistent solution. In our analysis, the rotating black hole acts as a particle accelerator and possesses the sensitivity to probe the symmergent gravity.

Analyzing Combustion Efficiency According to Spray Characteristics of Gas-Centered Swirl-Coaxial Injector

The momentum flux ratio (MFR) significantly affects the mixing characteristics and combustion efficiency of propellants in rocket engine injectors. The spray characteristics of three gas-centered swirl-coaxial injectors used in a full-scale combustion test were investigated according to the change in the momentum flux ratio. The difference in combustion efficiency was analyzed through the comparison with combustion test results using spray visualization and quantification. The spray cross-sectional shape and droplet distribution were measured using a structured laser illumination planar imaging technique. As the swirl effect was more apparent at a low MFR, the flow rate of the liquid that was sprayed outside was high. The flow rate of the liquid sprayed around the gas injection increased with the MFR. The Sauter mean diameter (SMD) of each injector liquid spray was obtained using the laser shadow imaging method. The SMD decreased as the MFR of all injector types increased, and the injector with a high liquid flow rate and small SMD injected towards the gas center exhibited higher combustion efficiency than the injector with a dominant liquid spray and the large SMD at a large injection angle. The outcomes of the study could help contribute to the increase in the combustion efficiency of the full-scale staged combustion cycle engine combustor.

Pavement Crack Detection in Infrared Images Using a DCNN and CCL Algorithm

In-pavement crack detection, image segmentation techniques can accurately identify and extract cracks in pavement images with complex backgrounds, however, due to the interference of noise and non-crack damage, the resulting irrelevant non-crack regions reduce the extraction accuracy. To address the above problems, this research presents a road crack segmentation model consisting of a skip connection and decoder of U-Net, residual blocks in the encoding part, and the connected components labeling algorithm (CCL) in the extremity. The proposed method, depth-wise separable convolution replaces the standard convolution to reduce the number of parameters and operation cost. Post-processing using the connected components labeling algorithm solves the interference of irrelevant non-cracked regions. 4710 infrared images are used for the training and testing of the model. The testing results show that the new method for the pavement crack detection in different shadowed images is satisfactory, the detection accuracy can be up to 92.23%, and the algorithm comparison proves that the proposed algorithm is much better than that by the widely used traditional algorithms. In terms of similarity, the Dice Similarity Coefficient (DSC) is improved by 5.97%, 5.22%, and 1.49% compared to FCN, U-Net, and DeeplabV3+ networks, respectively. Therefore, the method is effective in detecting cracks in different pavement IR images, and can significantly improve the accuracy of segmentation results, reduce the error rate, improve the segmentation accuracy and robustness, and can extract cracks in pavement IR images well.

Preserving friendly stacking and weighted shadows in selective scalable secret image sharing

Preserving friendly stacking and weighted shadows in selective scalable secret image sharing

Experimental Study of the Formation and Evolution of Gas Jets in Supersonic Combustion Chambers

A simple and efficient flow field visualization method (based on shadow imaging) was applied in a direct-connect test to explore the influence of the momentum flux ratio and the jet angle on the formation and evolution of nitrogen jets in supersonic combustion chambers. The test setup adopts a rectangular flow passage to simulate a flight condition with Mach number of 6 and altitude of 25 km. The experimental results showed that (a) the flow field visualization method adopted in this paper can clearly register the formation and evolution of the shock wave structure in the flow field and the windward shear vortex on the jet surface. (b) The evolution process of the windward shear vortex is significantly affected by the jet angle. In particular, the stretching position of the windward shear vortex changed when the jet angle was obtuse. (c) The bow shocks showed local distortion due to the periodic generation of large-scale shear vortexes. (d) Under the working conditions of the test, the largest instability of the flow field was found for a jet angle of 120°. This work provides, on one hand, the experimental basis for clarifying the formation and evolution mechanism of transverse gas jets, and on the other, valuable data that can be used to validate numerical simulations.

Recording of X-ray laser plasma radiation with new coded aperture imaging system

The paper presents a method for obtaining images in the study of the spatial structure of X-ray radiation of laser plasma with a new type of coded masks. In these experiments, a special type of self-supporting structure was chosen for the coded aperture. The shadow image created by the radiation passing through the aperture was recorded with a fluorescent imaging plate. An iterative algorithm based on a probabilistic approach to solving ill-posed problems was used to reconstruct the source image. The stability of the solution of the iterative method for masks of the considered type is studied, the results of applying the method for processing experimental data are presented, and the obtained images are compared with the images recorded with a pinhole camera. It has been established that the coded aperture used makes it possible to increase the sensitivity of the recording system by 2–3 orders of magnitude, while its use in combination with the developed mathematical algorithm allows one to obtain a higher spatial resolution than with a pinhole camera.

Black holes surrounded by Einstein clusters as models of dark matter fluid

We construct a novel class of spherically symmetric and asymptotically flat black holes and naked singularities surrounded by anisotropic dark matter fluid with the equation of state (EoS) of the form P_t=omega rho . We assume that dark matter is made of weakly interacting particles orbiting around the supermassive black hole in the galactic center and the dark matter halo is formed by means of Einstein clusters having only tangential pressure. In the large distance from the black hole we obtain the constant flat curve with the upper bound for the dark matter state parameter omega lesssim 10^{-7}. To this end, we also check the energy conditions of the dark matter fluid outside the black hole/naked singularity, the deflection of light by the galaxy, and the shadow images of the Sgr A^star black hole using the rotating and radiating particles. For the black hole case, we find that the effect of dark matter fluid on the shadow radius is small, in particular the angular radius of the black hole is shown to increase by the order 10^{-4}, upmu arcsec compared to the vacuum solution. For the naked singularity we obtain significantly smaller shadow radius compared to the black hole case. Finally, we study the stability of the S2 star orbit around Sgr A^star black hole under dark matter effects. It is argued that the motion of S2 star orbit is stable for values omega lesssim 10^{-7}, however further increase of omega leads to unstable orbits. Using the observational result for the shadow images of the Sgr A^star reported by the EHT along with the tightest constraint for omega found from the constant flat curve, we show that the black hole model is consistent with the data while the naked singularity in our model can be ruled out.

Application of proper orthogonal decomposition in particle image velocimetry in ocean engineering

Particle image velocimetry (PIV) plays a vital role in flow measurement. Eliminating the effects of overexposure and shadow in particle images is an urgent problem to be solved in the detailed flow measurement of ocean engineering. Seek a robust denoising method for bad test environments, and apply it to the PIV experiments to achieve dual denoising at the image preprocessing and data postprocessing. This study verified the superiority of the Proper Orthogonal Decomposition (POD) filter in pre- and postprocessing compared with traditional mathematical filters. Subsequently, the POD filter is applied to a practical project: the wake field measurement of bulk carrier. Regarding preprocessing, the POD filter is a valuable tool for objectively filtering typical high-frequency spatial noise from the energy perspective based on preserving the original information of particles to the greatest extent, effectively alleviating the impact of overexposure and shadow areas. Regarding postprocessing, the POD filter can fill the data gap by considering the surrounding flow characteristics. At the same time, the flow's spatial distribution and time evolution characteristics can be obtained by POD. The flow reconstructed by selecting the appropriate order model can clearly show the evolution characteristics of large-scale coherent structures, which may provide a deep understanding of complex flow field mechanisms.

Quantum grayscale image encryption and secret sharing schemes based on Rubik’s Cube

In order to encrypt and safely share images using quantum computer, a quantum grayscale image encryption scheme and a quantum grayscale image secret sharing scheme are proposed in this paper. According to Rubik’s Cube rotation method, this paper initially puts forward the quantum Rubik’s Cube rotation scrambling scheme (QRRSS) to permute the pixel position. Then, based on QRRSS, quantum XOR operation and quantum SWAP operation, we design the quantum image encryption scheme. Finally, we propose a quantum image secret sharing scheme. In the secret sharing scheme, one secret image and six cover images are encrypted. Quantum least significant bit (LSB) method is used to stego the secret image into four randomly chosen cover images in order to generate four shadow images. The shared secret image can be recovered if all the shadow images can be collected from all participants. We then design the whole quantum circuits of two proposed schemes and finish simulation experiments. The simulation results indicate that our encryption scheme and secret sharing scheme have good effect. It is worth noting that the computational complexity of our two proposed quantum algorithms is exponentially decreased than the classical counterparts.

Field-portable seawater toxicity monitoring platform using lens-free shadow imaging technology

The accidental spill of hazardous and noxious substances (HNSs) in the ocean has serious environmental and human health consequences. Assessing the ecotoxicity of seawater exposed to various HNS is challenging due to the constant development of new HNS or mixtures, and assessment methods are also limited. Microalgae viability tests are often used among the various biological indicators for ecotoxicity testing, as they are the primary producers in aquatic ecosystems. However, since the conventional cell growth rate test measures cell viability over three to four days using manual inspection under a conventional optical microscope, it is labor- and time-intensive and prone to subjective errors. In this study, we propose a rapid and automated method to evaluate seawater ecotoxicity by quantification of the morphological changes of microalgae exposed to more than 30 HNSs. This method was further validated using conventional growth rate test results. Dunaliella tertiolecta, a microalgae species without rigid cell walls, was selected as the test organism. Its morphological changes in response to HNS exposure were measured at the single cell level using a custom-developed device that uses lens-free shadow imaging technology. The ecotoxicity evaluation induced by the morphological change could be available in as little as 5 min using the proposed method and device, and it could be effective for 20 HNSs out of 30 HNSs tested. Moreover, the test results of six selected HNSs with high marine transport volume and toxicity revealed that the sensitivity of the proposed method extends to half the maximum effective concentration (EC50) and even to the lowest observed effective concentration (LOEC). Furthermore, the average correlation index between the growth inhibition test (three to four days) and the proposed morphology changes test (5 min) for the six selected HNSs was 0.84, indicating great promise in the field of various point-of-care water quality monitoring. Thus, the proposed equipment and technology may provide a viable alternative to traditional on-site toxicity testing, and the potential of rapid morphological analysis may replace traditional growth inhibition testing.

Image shadow removal algorithm guided by progressive attention mechanism

Image shadow removal algorithm guided by progressive attention mechanism

Secret image sharing scheme with lossless recovery and high efficiency

As a well-known secret image sharing scheme, Thien-and-Lin’s scheme generates shadow images of reduced size, which is beneficial for storage, transmission, and processing. However, it has some drawbacks, such as lossy recovery, needing extra secure transmission channels. For decades, many improved schemes have been proposed, but none can solve all the drawbacks simultaneously. Therefore, this paper proposes a (k,n)-threshold secret image sharing scheme, trying to solve the drawbacks comprehensively. In the sharing phase, two 8-bit pixels of the secret image are linked as a 16-bit secret value, and all the coefficients of the generating polynomial are used to embed secrets. Then, Shamir’s secret sharing is implemented in Galois Field GF(65,537), and the only invalid share 65,536 will be set to 0. In the recovery phase, lossless recovery can be realized through neighborhood consistency calculation. To avoid key transmission, we develop a robust statistical invariance index of the secret image to generate permutation keys. Then Arnold permutation is performed to prevent information leakage. The proposed scheme can realize lossless recovery efficiently, without pixel expansion, complex preprocessing, and extra secure transmission channels. Theoretical analysis and experiments are given to validate the effectiveness of our scheme.