Backlit Images Research Articles

Restoration of UAV-Based Backlit Images for Geological Mapping of a High-Steep Slope.

Unmanned aerial vehicle (UAV)-based geological mapping is significant for understanding the geological structure in the high-steep slopes, but the images obtained in these areas are inevitably influenced by the backlit effect because of the undulating terrain and the viewpoint change of the camera mounted on the UAV. To handle this concern, a novel backlit image restoration method is proposed that takes the real-world application into account and addresses the color distortion issue existing in backlit images captured in high-steep slope scenes. Specifically, there are two main steps in the proposed method, which consist of the backlit removal and the color and detail enhancement. The backlit removal first eliminates the backlit effect using the Retinex strategy, and then the color and detail enhancement step improves the image color and sharpness. The author designs extensive comparison experiments from multiple angles and applies the proposed method to different engineering applications. The experimental results show that the proposed method has potential compared to other main-stream methods both in qualitative visual effects and universal quantitative evaluation metrics. The backlit images processed by the proposed method are significantly improved by the process of feature key point matching, which is very conducive to the fine construction of 3D geological models of the high-steep slope.

Influence of deposited liquid structures on the separation efficiency of thin oleophilic fiber layers of mist filters

The presence of oil mists constitutes a significant hazard to both, human health and the environment. In industrial applications, the effective separation of these mists typically relies on the utilization of multi-layer nonwoven coalescence filters. The underlying mechanisms governing droplet deposition, liquid transport within the filter matrix, and the evolution of the overall differential pressure have been extensively documented in the existing literature. However, limited and contradictory information is currently available regarding the impact of deposited liquid structures under varying saturation levels on the separation efficiency of coalescence filters.In this study, the influence of an increased liquid saturation at different filtration velocities on the fractional and total separation efficiency of thin porous non-woven fiber layers comparable to the first fiber layers of the first filter layer of commercially utilized coalescence filters are evaluated. As the oil load increases to a saturation of S≤ 0.4, the total separation efficiency (number-based) decreases, for all investigated filtration velocities. In addition, a shift of the most penetrating particle size (MPPS) to smaller droplet sizes and a decrease of the MPPS efficiency is observed. This decrease is attributed to a higher interstitial velocity resulting from the accumulation of liquid within the filter matrix, leading to a lower fractional separation efficiency in the diffusion regime. However, at saturation levels S≥ 0.6, the separation efficiency (meaning both, fractional and total separation efficiency) begins to increase due to the formation of partial oil films, leading to a blockage of void space. These films significantly enhance inertial separation. At the highest investigated saturations (S=0.8), the highest separation efficiencies due to a nearly complete coverage of the filter layers by an oil film are observed. The film formation is confirmed through backlit images of the oil-loaded filter material. Furthermore, an increase of the MPPS efficiency for a saturation of S=0.8 with increasing filtration velocity due to increased diffusional separation is recorded, which cannot yet conclusively answered by the authors. Additionally, the differential pressure across the fiber sheets is presented, revealing a more pronounced influence of the oil film on the differential pressure at increasing filtration velocities.

Spatio-temporal dynamics of an acoustically forced cryogenic coaxial jet injector

This study focuses on the application of dynamical systems theory to characterize the local susceptibility of a nonreacting, cryogenic, coaxial-jet, rocket injector to transverse acoustics. This is achieved using trajectories of the phase space obtained from high-speed imaging data, which reveal the underlying dynamical states of the system. Recurrence analysis is then used to obtain regular patterns in low-dimensional sub-space plots and provide a measure of the local response through recurrence quantification analysis. Of particular interest is quantification of the spatio-temporal coupling of the jet with the external acoustics as a function of the relative momentum flux ratio between the outer and inner jets. At lower outer-to-inner jet momentum flux ratios (J < 1), the jets have a relatively strong local response to acoustic coupling in the near field. This is followed by a sharp drop in this response further downstream where a broad range of instabilities indicates turbulent breakdown of the acoustic mode. This is in contrast to higher outer-to-inner jet momentum flux ratios (J > 1), for which the jets are intermittently coupled to the acoustic mode throughout the entire axial domain due to the presence of a second harmonic or natural instability mode. These dynamical systems analysis tools are used in conjunction with wavelet filtering to improve the utility of high-speed backlit images and are qualitatively consistent with wavelet analysis of the acoustic mode within the flow. The utility of these methods for quantifying the local susceptibility of turbulent coaxial jets to acoustic perturbations can provide powerful insight for the design and optimization of passive or active control systems for bipropellant rocket injectors and other potential propulsion applications.

Diffusiophoresis of latex driven by anionic nanoparticles and their counterions

HypothesisDiffusiophoresis of colloidal latex particles has been reported for molecular anions and cations of comparable size. In the present study, this phenomenon is observed for two types of charged colloids acting as multivalent electrolyte: (i) anionic charge-stabilised silica nanoparticles or (ii) minimally-charged sterically-stabilised diblock copolymer nanoparticles. ExperimentsUsing a Hele-Shaw cell, a thin layer of relatively large latex particles is established within a sharp concentration gradient of nanoparticles by sequential filling with water, latex particles and nanoparticles. Asymmetric diffusion is observed, which provides strong evidence for diffusiophoresis. Quantification involves turbidity measurements from backlit images. FindingsThe latex particles diffuse across a concentration gradient of charged nanoparticles and the latex concentration front scales approximately with time1/2. Moreover, the latex particle flux is inversely proportional to the concentration of background salt, confirming electrostatically-driven motion. These observations are consistent with theory recently developed to account for diffusiophoretic motion driven by multivalent ions.

Multi-illumination Mapping-Based Fusion Method for Low-Light Area’s Visibility and Backlit Image Enhancement

Multi-illumination Mapping-Based Fusion Method for Low-Light Area’s Visibility and Backlit Image Enhancement

Contrast enhancement of region of interest of backlit image for surveillance systems based on multi-illumination fusion

The surveillance images under backlit conditions is a potential and challenging research problem in image processing and computer vision. Low contrast regions of interest of backlit images form an indiscernible part for the real-time surveillance and biometrics applications. However, current state-of-the-art techniques typically offer limited dark-region contrast enhancement, are susceptible to colour distortion. This research work uses region of interest segmentation and a transfer learning-based strategy to improve the contrast of the dark intensity regions in backlit image using multi-illumination mappings, motivated by its usefulness. To generate a diversified collection of illumination-maps and enhance the brightness and contrast of the backlit image, the proposed framework applies the varied set of log and gamma transforms. The experimental findings confirm the assertion that the proposed method provides better performance than state-of-the-art methods both objectively and subjectively.

Enhancement of underwater shock wave by coupling electrical explosion and al-powder-suspension combustion: Facing advanced reservoir stimulation technology

The development of fossil energy requires eco-friendly and high-efficient approaches, especially in contemporarily low-carbon scenarios. Using the high-power pulsed discharge to induce fractures has drawn increasingly academic and industrial attention in reservoir stimulation. Therein, the electrical wire explosion is commonly adopted as the pulsed discharge load to transfer electrical energy to mechanical one (shock wave and plasma bubble) efficiently. To strengthen mechanical loadings, a discharge capsule with a metallic wire inside Al-powder suspension has been designed and tested. Experiments were performed with a μs-timescale pulsed power source with stored energy from 150 to 750 J, and the electrical explosion were diagnosed via high-speed photography, electrophysical, and mechanical measurements. The experiment shows that there is an optimal concentration of Al-powder suspension in order to obtain the maximum peak pressure of shock wave for a given discharge condition. Too high or low concentrations of the aluminum powder will cause a lower peak pressure. This paper shows that at the stored energy of 500 J, when the concentration of Al-powder suspension is 20 g/L, the peak pressure can reach 4.81 ± 0.27 MPa, which is 2.01 times as large as the shock wave generated by the electrical explosion under the same conditions in pure water. Through the electrophysical measurement, it is found that the aluminum powder almost does not affect the phase transition of the wire. However, in the subsequent plasma formation, the gaseous reaction products make the discharge channel more complex and in a higher pressure density state, which is shown by the increase of channel resistance. Through the backlit images taken by the high-speed camera, it is obvious that two discrete strong shock waves can be seen in the Al-powder-suspension environment.

PLUME ANALYSIS OF PLUNGING LIQUID JETS WITH FLOOR INTERACTIONS USING STEREOGRAPHIC BACKLIT IMAGING

Plunging liquid jets occur when a liquid jet travels through a gas and enters a liquid pool. They are studied in order to understand and model the highly efficient gas-liquid mixing in the resulting bubble plume. Among the aspects of plunging jets studied, compression effects at the bottom or within the pool, while relatively common in application, remain less understood in current literature. The presence of a tank floor spreads the resultant bubble plume which reduces the flow resistance between the rising bubble plume and the incoming liquid jet. The effect of the tank floor on the overall entrainment and mixing is unknown. In order to understand the compression effects of the plume-floor interaction, a liquid-filled tank was designed to simulate multiple tank depths. This work describes the apparatus used to produce a plunging jet with floor effects, as well as the image analysis methodology for identifying and comparing plume formations. Data were collected for multiple liquid flow rates encompassing different entrainment regimes as well as multiple plate positions, varying the level of plume and base interaction. Stereographic backlit images were acquired and several different identification methods are described to better define and compare bubble plume features. Limitations in the image analysis procedures are also described.

Low-Artifact and Fast Backlit Image Enhancement Method Based on Suppression of Lightness Order Error

Low-Artifact and Fast Backlit Image Enhancement Method Based on Suppression of Lightness Order Error

BacklitNet: A dataset and network for backlit image enhancement

Backlit images are usually taken when the light source is opposite to the camera. The uneven exposure (e.g., underexposure on the foreground and overexposure on the background) makes the backlit images more challenging than general image enhancement tasks that only need to increase or decrease the exposure on the whole images. Compared to traditional approaches, Convolutional Neural Networks perform well in enhancing images due to the abilities of exploiting contextual features. However, the lack of large benchmark datasets and specially designed models impedes the development of backlit image enhancement. In this paper, we build the first large-scale BAcklit Image Dataset (BAID), which contains 3000 backlit images and the corresponding ground truth manually adjusted by trained photographers. It covers a broad range of categories under different backlit conditions in both indoor and outdoor scenes. Furthermore, we propose a saliency guided backlit image enhancement network, namely BacklitNet, for robust and natural restoration of backlit images. In particular, our model innovatively combines a nested U-structure with bilateral grids, which enables fully extracting multi-scale saliency information and rapidly enhancing arbitrary resolution images. Moreover, a carefully designed loss function based on prior knowledge of brightness distribution of backlit images is proposed to enforce the network to focus more on backlit regions during the training phase. We evaluate the proposed method on the BAID dataset and two public small-scale backlit image datasets. Experimental results demonstrate that our method performs favorably against the state-of-the-art approaches.

A single backlit image enhancement method by image fusion with a weight map for improvement of dark area’s visibility

A single backlit image enhancement method by image fusion with a weight map for improvement of dark area’s visibility

An improved fusion strategy based on transparency-guided backlit image enhancement

An improved fusion strategy based on transparency-guided backlit image enhancement

Multiple feature-based contrast enhancement of ROI of backlit images

Multiple feature-based contrast enhancement of ROI of backlit images

Spatio-temporal dynamics and disintegration of a fan liquid sheet

The dynamic behavior and disintegration mechanisms of a fan liquid sheet in a quiescent atmosphere are investigated over a broad range of differential injection pressures up to Δp≈70 bar through experiments, proper orthogonal decomposition (POD) and spectral analyses, and linear stability analysis (LSA). By fan liquid sheet, we mean a diverging and attenuating liquid stream emanating from a flat fan nozzle with high velocity. High spatiotemporal resolution backlit images reveal the formation-growth-fragmentation process of bag-like structures along the fan liquid sheets, which we predict to be responsible for the overall breakup of the sheets through a mechanism known as “wavy corridor.” Therefore, we propose a conjugate model based on LSA to take into account the role of different shear and surface tension-driven instabilities in defining the liquid sheet intact radius and primary droplet sizes. The predictions of LSA from the dynamic features of the liquid sheets, which mainly depend on the sheet Weber number We, are consistent with the quantitative results obtained from the POD and spectral analyses of the images. While the Strouhal number St and the intact radius R of the fan liquid sheets reduce like We−1/3 with increasing We, the volume median diameter of primary droplets decreases like We−11/12. An image feature consolidation technique along with a machine-learning technique, receiver operating characteristic curve analysis, was used to estimate the mean diameter of spray droplets with a large range of sizes.

Region of interest enhancement for backlit images using global tone mappings and fusion

ABSTRACT Backlit images simultaneously include dark as well as light regions of intensity. Objects in dark and low-contrast regions are complex for humans to perceive. In particular, such parts are selected as the image's region of interest (ROI). In backlit images, ROI is typically very dark and of low contrast, which makes visualization difficult. This paper explores and presents an approach for contrast enhancement and preserving the naturalness of the ROI of the backlit image. The proposed methodology considers stretching the contrast and balancing other aspects of the ROI, such as textural details, visibility, etc. In the last stage, a fusion-based approach is carried out to obtain enhanced ROI of the backlit image. It also examines the experimental results of the proposed method using various steps and, based on the validation, confirms that the proposed solution produces better results for the ROI of the backlit image than the other state-of-the-art methods.

Interaction between negative corona discharge and droplet emission from liquid Taylor cone

We investigated the behavior of droplets, the Taylor cone tip, and discharge current characteristics in electrospraying with negative corona discharge, and analyzed the interaction among them in the time scale of several micro seconds. Negative corona discharges using 1 wt% sodium dodecyl sulfate solution or ethylene glycol as liquid cathode were investigated, and the discharge current pulse had a distinctive structure with serial pulse trains. The pulse train structure indicated that the discharges from the Taylor cone are in the form of Trichel pulses with a dynamic cathode. We found that the electric field, liquid conductivity, and liquid viscosity had no significant effect on the discharge current characteristics, with the exception of the current peak value, whereas a higher electric field or higher liquid viscosity led to extended pulse train intervals and durations. These effects can be attributed to the change in time scale of the cone tip curvature variation. The above results indicate that the curvature radius of the cone tip dominates the discharges from the Taylor cone. The emission and transfer of droplets between electrodes were observed using back-lit images and Mie-scattered light images taken by a high-speed camera. The droplet emission was synchronized with the leading current in the Trichel pulses. The terminal velocity of the droplets transferring discharge gap was proportional to the revised electric field. The experimental results indicate that the droplet emission mechanism from the Taylor cone with discharges is supposed to differ from that without discharges explained by the Rayleigh limit. The reasonable explanation for the droplet emission mechanism is that the droplets are torn off the liquid cone tip by the strong electric field associated with discharges.

Effect of 2, 5-dimethylfuran concentration on micro-explosive combustion characteristics of biodiesel droplet

Micro-explosive combustion is considered as an effective way to improve combustion efficiency in combustor. In this work, the micro-explosive combustion characteristics of biodiesel and DMF blended droplet are investigated using high-speed backlit image technique. The droplet is suspended at the intersection of two quartz fiber and ignited by a pair of electrodes. Flame temperature and soot concentration are measured using two-color pyrometry method. Moreover, two new parameters are proposed to analysis droplet micro-explosion, namely droplet instability and breakup index. The results shown that the instability of DMF25BD75, DMF50BD50 and DMF75BD25 droplets is mainly caused by bubbles coalescence, internal circulation of bubbles, micro-explosion and vapor jetting. The low-temperature flame region is mainly located near the droplet surface and flame edge. However, the soot concentration is highest in these two regions. The combustion of blended droplet includes a micro-explosive combustion stage and a stable combustion stage. Four modes of secondary atomization is determined according to droplet breakup index. When the DMF concentration is 50% and 75%, the burning rate is 9% and 37.5% higher than diesel, which is expected to realize rapid and high-efficient combustion.

A combined experimental and computational study of flow-blurring atomization in a twin-fluid atomizer

A twin-fluid pneumatic injector system with coaxial liquid and air streams mixed slightly upstream of the outlet, is studied in a cross-flow arrangement to understand its working principle. The gap between the orifice and the liquid tube, where the air and liquid cross-flow occurs, is known to determine the modes of working of the atomizer for the given operating flow rates of air and liquid. The two distinct modes, namely the flow focusing (FF) and flow blurring (FB) are observed in the present study, and the transition from FF to FB mode is explored using optical visualization. The characteristics of the internal two-phase flow mixing that occurs due to backflow recirculation in FB mode are also investigated by performing large eddy simulation (LES) using the volume of fluid (VoF) approach. The results of the numerical simulation are validated with experimental observations for the length of backflow recirculation observed in the liquid tube. The present study demonstrates the development of multiple microjets, which explains experimental observations of the lack of core jet and the almost uniform distribution of radial Sauter mean diameter (SMD) reported in the literature. The high-resolution backlit image of a scaled-up transparent injector with a 6 mm orifice diameter validates the numerical results that describe the internal two-phase flow.

A Real-Time 3D Measurement System for the Blast Furnace Burden Surface Using High-Temperature Industrial Endoscope.

Capturing the three-dimensional (3D) shape of the burden surface of a blast furnace (BF) in real-time with high accuracy is crucial for improving gas flow distribution, optimizing coke operation, and stabilizing BF operation. However, it is difficult to perform 3D shape measurement of the burden surface in real-time during the ironmaking process because of the high-temperature, high-dust, and lightless enclosed environment inside the BF. To solve this problem, a real-time 3D measurement system is developed in this study by combining an industrial endoscope with a virtual multi-head camera array 3D reconstruction method. First, images of the original burden surface are captured using a purpose-built industrial endoscope. Second, a novel micro-pixel luminance polarization method is proposed and applied to compensate for the heavy noise in the backlit images due to high dust levels and poor light in the enclosed environment. Third, to extract depth information, a multifeature-based depth key frame classifier is designed to filter out images with high levels of clarity and displacement. Finally, a 3D shape burden surface reconstruction method based on a virtual multi-head camera array is proposed for capturing the real-time 3D shape of the burden surface in an operational BF. The results of an industrial experiment illustrate that the proposed method can measure the 3D shape of the entire burden surface and provide reliable burden surface shape information for BF control.

Backlit images enhancement using global tone mappings and image fusion

The authors present a method for the enhancement of backlit images, i.e. images in which the main source of light is behind the photography subject. These images contain, simultaneously, very dark and very bright regions. In this situation, a single tone mapping function is unable to enhance the whole image. They propose the use of several such tone mappings, some of them enhancing the dark regions while others enhancing the bright regions, and then the combination of all these results using an image fusion algorithm. Qualitative and quantitative results confirm the validity of the proposed method.