High Frame Rate Camera Research Articles

Heat Loss Analysis of Flow Boiling Experiments Onboard International Space Station with Unclear Thermal Environmental Conditions (1st Report: Subcooled Liquid Flow Conditions at Test Section Inlet)

Two series of flow boiling experiments have been conducted onboard the International Space Station (ISS) as a part of the TPF (Two-Phase Flow) experiment promoted by JAXA during July 2017–March 2018, February 2019–July 2019. Microgravity data on two-phase flow and heat transfer in flow boiling of n-Perfluorohexane (FC-72) have been obtained by a copper heated test tube and a transparent glass heated tube in a wide experimental range of mass velocity, liquid subcooling, vapor quality and heat flux. Furthermore, detailed two-phase flow behaviors have been observed by using high frame rate camera in the unheated observation section. In order to elucidate the accurate influence of gravity on flow boiling, it is essential to compare the heat transfer data and two-phase flow behaviors obtained under normal (terrestrial) gravity and microgravity environments at the same flow and heating conditions. However, both experiments cannot be performed by using the same experimental apparatus and under the same thermal environmental conditions. In addition, the heat loss cannot be negligible due to the forced avionics air flow inside the experimental apparatus in ISS. Therefore, exact evaluation of the fluid conditions at the inlet of the heated test tube requires the heat loss model with high-accuracy. In the present paper, the heat loss models for evaluating the degree of liquid subcooling at the inlet of the heated test tube and net heat flux from the heated tube to test fluid has been developed by using the results of preliminary heat loss experiments conducted onboard ISS. The correction of the degree of liquid subcooling by the proposed heat loss models is not negligible for the accurate analysis of gravity effects. The accuracy of the heat loss models has been verified through the evaluation of heat transfer coefficients for single-phase turbulent forced convection obtained from the heating experiments onboard ISS.

Continuous-Time Fast Motion of Explosion Fragments Estimated by Bundle Adjustment and Spline Representation Using HFR Cameras

This paper introduces a continuous-time fast motion estimation framework using high frame-rate cameras. To recover the high-speed motions trajectory, we inherent the bundle adjustment using a different frame-rate strategy. Based on the optimized trajectory, a cubic B-spline representation was proposed to parameter the continuous-time position, velocity and acceleration during this fast motion. We designed a high-speed visual system consisting of the high frame-rate cameras and infrared cameras, which can capture the fast scattered motion of explosion fragments and evaluate our method. The experiments show that bundle adjustment can greatly improve the accuracy and stability of the trajectory estimation, and the B-spline representation of the high frame-rate can estimate the velocity, acceleration, momentum and force of each fragments at any given time during its motion. The related estimated result can achieve under 1% error.

Bio-Inspired Video Enhancement for Small Moving Target Detection.

Moving targets at a very large distance from a camera appear small and of low contrast. The low signal-to-noise-ratio and the presence of clutter in the background degrade the detection performance of conventional moving object detection techniques. To address these challenges, we propose temporal pre-processing of video frames using a biologically-inspired vision model. The bio-inspired model consists of multiple layers of processing analogous to the photoreceptor cells in the visual system of small insects. The adaptive filtering mechanism in the photoreceptor cells suppresses clutter and expands the possible range of input signal changes which improves the target background contrast. We perform experiments on real world video sequences of small moving targets captured with a high bit depth, high resolution and high frame-rate camera. Experimental results show that the biological vision based pre-processing leads to improved detection performance when used in conjunction with a variety of computer vision based moving object detection algorithms. The temporal bio-processing alone has improved the area under the receiver operating characteristic (AUROC) curve of the best performing algorithm by 75.4%. Our results suggest that the bio-inspired pre-processing has strong potential to become a key component of a practical small target detection system.

Markerless Rat Behavior Quantification With Cascade Neural Network.

Quantifying rat behavior through video surveillance is crucial for medicine, neuroscience, and other fields. In this paper, we focus on the challenging problem of estimating landmark points, such as the rat's eyes and joints, only with image processing and quantify the motion behavior of the rat. Firstly, we placed the rat on a special running machine and used a high frame rate camera to capture its motion. Secondly, we designed the cascade convolution network (CCN) and cascade hourglass network (CHN), which are two structures to extract features of the images. Three coordinate calculation methods—fully connected regression (FCR), heatmap maximum position (HMP), and heatmap integral regression (HIR)—were used to locate the coordinates of the landmark points. Thirdly, through a strict normalized evaluation criterion, we analyzed the accuracy of the different structures and coordinate calculation methods for rat landmark point estimation in various feature map sizes. The results demonstrated that the CCN structure with the HIR method achieved the highest estimation accuracy of 75%, which is sufficient to accurately track and quantify rat joint motion.

Multi-speckle diffuse correlation spectroscopy to measure cerebral blood flow.

We present a multi-speckle diffuse correlation spectroscopy (DCS) system for measuring cerebral blood flow in the healthy adult human brain. In contrast to the need for a high frame rate camera to measure the multi-speckle intensity auto-correlation, we employ a low frame rate camera to measure the auto-correlation using the recently introduced multi-step volterra integral method (MVIM). The results are validated by comparison against the blood flow measured using standard DCS system.

HFR Projector Camera Based Visible Light Communication System for Real-Time Video Streaming.

This study develops a projector–camera-based visible light communication (VLC) system for real-time broadband video streaming, in which a high frame rate (HFR) projector can encode and project a color input video sequence into binary image patterns modulated at thousands of frames per second and an HFR vision system can capture and decode these binary patterns into the input color video sequence with real-time video processing. For maximum utilization of the high-throughput transmission ability of the HFR projector, we introduce a projector–camera VLC protocol, wherein a multi-level color video sequence is binary-modulated with a gray code for encoding and decoding instead of pure-code-based binary modulation. Gray code encoding is introduced to address the ambiguity with mismatched pixel alignments along the gradients between the projector and vision system. Our proposed VLC system consists of an HFR projector, which can project 590 × 1060 binary images at 1041 fps via HDMI streaming and a monochrome HFR camera system, which can capture and process 12-bit 512 × 512 images in real time at 3125 fps; it can simultaneously decode and reconstruct 24-bit RGB video sequences at 31 fps, including an error correction process. The effectiveness of the proposed VLC system was verified via several experiments by streaming offline and live video sequences.

Chemical and physical transformations of carbon-based nanomaterials observed by liquid phase transmission electron microscopy

Abstract

Monitoring and detection of meltpool and spatter regions in laser powder bed fusion of super alloy Inconel 625

Additive manufacturing is being adopted to produce metal parts directly from digital design with applications in automotive, aerospace, and biomedical products. Laser powder bed fusion (LPBF) process is a viable technology for this purpose that utilizes a high-power laser beam which follows layer-to-layer scanning of predefined paths on a metal powder bed. In situ monitoring of LPBF process is essential to detect the localized meltpool, its vicinity, and material spatter around it with a goal to control the health of the meltpool. Among many alternatives, high-fidelity video monitoring can provide cost-effective insights to the on-going process to detect changes in meltpool and its vicinity that can further be integrated into an adaptive control system. For this purpose, a high frame rate camera was employed for in situ viewing of meltpool regions during laser fusion of a super alloy, Inconel 625, powder material to be able to improve the process control capability. The size and shape of the meltpool and the heat affected region detected via in situ viewing represent the sources of information to detect possible anomalies and defects. These acquired video volumes were processed and analysed using statistical process control (SPC) charts. The results indicate that some occurrences of undermelting, overmelting, and material spatter can be detected that can then be correlated to localized defects, delamination, and layer separation.

Apparatus design for measuring electrostatic charge transfer due to particle-particle collisions

A novel apparatus was designed, built and tested to study the magnitude and direction of charge transfer in particle-particle collisions of insulator particles. This design ensured that the measured change in the charge of each particle was solely due to the binary collision between the particles. The collisions were confirmed by monitoring the particle trajectories using a high frame-rate camera coupled with particle-tracking software. This apparatus can aid in understanding the charge transfer mechanisms behind particle-particle charge transfer, leading to the development of an electrostatic model to simulate particle-particle contact charging in gas-solid flows. Upon preliminary testing of this apparatus with 3.18 mm diameter polytetrafluoroethylene (PTFE) particles, it was confirmed that triboelectrification solely due to the particle-particle collision can be observed. It was found that, if the particles carry low charges relative to their charge saturation point, their initial charge before collision does not dictate the direction of charge transfer.

Multi-exposure laser speckle contrast imaging using a video-rate multi-tap charge modulation image sensor.

Multi-exposure laser speckle contrast imaging (MELSCI) systems based on high frame rate cameras are suitable for wide-field quantitative measurement of blood flow. However, high-speed camera-based MELSCI requires high power consumption, large memory, and high processing capability, which may lead to relatively large and expensive hardware. To realize a compact and cost-efficient MELSCI system, we discuss an application of the multi-tap CMOS image sensor originally designed for time-of-flight range imaging. This image sensor operated in the global shutter mode and every pixel was provided with multiple charge-storage diodes. Multiple images for different exposures were acquired simultaneously because exposure patterns were programmable to implement an arbitrary exposure duration for each tap. The frame rate was close to video frame rates (30 frames per second (fps)) regardless of the exposure pattern. The feasibility of the proposed method was verified by simulations that were performed with real speckle images captured by a high-speed camera at 40 kfps. Experiments with a four-tap CMOS image sensor demonstrated that a flow speed map was obtained at a moderate frame rate such as 35 fps for a moving ground glass plate and 45 fps for flowing Intralipose, which were linearly moved at speeds of 1-5 mm/s.

Flicker Reduction Method for High Frame Rate Camera on Smartphone

Flicker Reduction Method for High Frame Rate Camera on Smartphone

Event-Guided Structured Output Tracking of Fast-Moving Objects Using a CeleX Sensor

In this paper, we propose an event-guided support vector machine (ESVM) for tracking high-speed moving objects. Tracking fast-moving objects with low frame rate cameras is always difficult due to motion blur and large displacements. The accuracy problem can be solved by using high frame rate cameras at the expense of tremendous computational cost. For this issue, our ESVM incorporates event-based guiding methods into the traditional structured support vector machine to improve the tracking accuracy at a relatively low-complexity level. The event-based guiding methods include two models, event position guided search localization and event intensity guided sample supplement, which are based on the event features of the CeleX motion sensor. The motion sensor continuously responds to intensity change, which is generally related to object motion. Once it has detected intensity change, the motion sensor outputs event packages, and each of them contains the pixel location, time stamp, and pixel illumination. The generated events are continuous in the temporal domain and thus record the motion trajectory of fast-moving objects, which cannot be fully captured by frame-based cameras. In this paper, we convert high-speed test sequences into sequences of spiking events recorded by the CeleX motion sensor. Our approach presents fairly high computational efficiency, and experiments over sequences from multiple tracking benchmarks demonstrate the superior accuracy and real-time performance of our method, compared to the state-of-the-art trackers.

Experimental Testing of Targets for a High Accuracy Microtarget Supply (HAMS) System on the Gemini Laser System

It is widely understood within the high-power laser community that recent developments in diode pumped and high repetition rate laser systems will give unprecedented access to laser shots. This will provide a challenge for target fabrication in making enough experimental samples. While in the past access to facilities and shot rates during access periods have been the limiting factor for high power laser experiments this will soon not be the case. There has already been a shift in development of the user base from fundamental science experiments to industrial applications using the laser experiment as a reliable source for secondary aims. The Astra Gemini laser system has been operating at a high repetition rate for high intensity (0.5PW) experiments for a number of years and the Central Laser Facility has developed a target methodology to deliver to the user community the maximum number of solid targets and to fully utilise the available time on the laser. Targets for the High Accuracy Microtarget Supply (HAMS) system have been tested and have been proven to survive in a manner to allow shot rates comparable with the available laser repetition rate (0.1Hz). Investigations into target geometry have been carried out and debris production has been studied by high frame rate camera imaging. The study of the relationship between target geometry and debris production has allowed the design of optimal target support infrastructure, such as aperture size and structure, for high rep rate experiments on the Gemini system.

An Investigation into Dynamic Puncture Resistance of the Polyester Needled Nonwoven Geotextiles using Video Processing Technique

Abstract In this study, the dynamic puncture behavior of nonwoven needle-punched polyester geotextiles has been studied using video processing technique. Twenty-seven needle-punched geotextile samples were produced by changing areal weight, needle penetration depth and punch density as independent variables. Cone drop test was carried out on the samples. In addition to measuring the hole diameter (HD), the video processing technique with a high frame rate camera was employed to calculate the energy absorbed by geotextile fabric up to puncture point (Ep) and the hole expansion energy (Ee). Multiple linear regression method was used to develop the predicting relationships between independent and reply variables. The models showed that an increase in areal weight results in an increase in Ep, whereas it causes a decrease in Ee and HD. Moreover, increasing punch density and needle penetration depth, leads to less Ep, and more Ee and HD. In addition, it was also found that significant relationships exist for Ep-HD and Ee-HD.

Tensile properties of Zr70Ni16Cu6Al8 BMG at room and cryogenic temperatures

The mechanical behaviour in tension of a hypoeutectic Zr70Ni16Cu6Al8 Bulk Metallic Glass (BMG) was studied at room (295 K) and cryogenic temperatures (150 K and 77 K) using various strain rates between 10−4 and 10−1 s−1. The yield strength was found to increase at lower temperatures with average values increasing by 16%, from 1503 MPa at 295 K to 1746 MPa at 77 K. The Zr-based BMG was found to exhibit tensile plastic elongation of about 0.4% before fracture at room temperature and high strain rates (10−1 s−1). Even higher tensile plasticity was recorded at low temperatures; plastic deformation was found highest at the intermediate temperature (150 K) reaching remarkable plastic strains in the order of 3.9%, while values up to 1.5% were recorded at 77 K. The lateral surface of the tensile specimens was observed in-situ during deformation using a high frame rate camera offering interesting insights with regard to the deformation mechanisms. Room temperature plasticity occurred through the formation and interaction of several nucleated shear bands before critical failure, while at intermediate and liquid nitrogen temperatures, most of the plastic deformation was accommodated through stable flow within a single shear band.

All-optical imaging and tracking technology for rectilinear motion targets through scattering media

Light scattering is a main factor that restricts optical transmission and deteriorates optical imaging performance. All-optical imaging for moving targets through complex scattering media is one of the most challenging techniques. In this paper, a method for real-time tracking of moving targets through scattering medium is presented by utilizing optical memory-effect and autocorrelation of speckle difference. In the experiment on imaging through a scattering medium, an object is hidden at a distance u behind a highly scattering medium. The object is illuminated by a spatially incoherent pseudothermal light source. The light is diffused through the scattering medium. Camera placed at a distance u0 on the other side of the medium records the pattern of the scattered light. According to the theory of optical memory-effect, the process of scattering imaging is a convolution process of point spread function (PSF) and object. In the procedure of object moving, the scattered signals from two frames are captured. The background noise could be removed by subtracting the two captured image. Then, the autocorrelation operation calculates the speckle difference, and hidden targets can be effectively reconstructed with the phase retrieval algorithm. The experiment demonstrates the imaging of targets with different speeds. The results have shown that the faster the speed, the worse the imaging quality is. High-speed moving objects can be imaged by using a high frame rate camera to reduce the exposure time or by disambiguating the speckle pattern. In subsequent experiments, the distance of the target movement is calculated with the magnification of the system. The collected two frames of speckle must be within the same memory effect angle. Only in this way can the calculation accuracy of the motion distance be guaranteed. With the moving of the target, the cross-correlation information of the target appears at different positions of the speckle difference autocorrelation map. Finally, according to the cross-correlation of the target at different locations, the real-time tracking of the moving target can be realized. Due to the Gaussian distribution of the laser beam, the cross-correlation intensity of the speckle difference autocorrelation map decreases with the object moving further. Therefore the target moving range is limited by the laser beam diameter, intensity distribution and camera field angle. It is verified experimentally that the imaging and tracking of moving targets which are hidden behind the ground glass can be achieved successfully by using this method. This kind of imaging and real-time tracking technology for targets moving through the scattering medium has important potential applications in biomedicine and other fields.

Webcam‐based system for video‐oculography

Video‐oculography (VOG) is a tool providing diagnostic information about the progress of the diseases that cause regression of the vergence eye movements, such as Parkinson's disease (PD). The majority of the existing systems are based on sophisticated infra‐red (IR) devices. In this study, the authors show that a webcam‐based VOG system can provide similar accuracy to that of a head‐mounted IR‐based VOG system. They also prove that the authors’ iris localisation algorithm outperforms current state‐of‐the‐art methods on the popular BioID dataset in terms of accuracy. The proposed system consists of a set of image processing algorithms: face detection, facial features localisation and iris localisation. They have performed examinations on patients suffering from PD using their system and a JAZZ‐novo head‐mounted device with IR sensor as reference. In the experiments, they have obtained a mean correlation of 0.841 between the results from their method and those from the JAZZ‐novo. They have shown that the accuracy of their visual system is similar to the accuracy of IR head‐mounted devices. In the future, they plan to extend their experiments to inexpensive high frame rate cameras which can potentially provide more diagnostic parameters.

Dynamic measurements and simulations of airborne picolitre-droplet coalescence in holographic optical tweezers.

We report studies of the coalescence of pairs of picolitre aerosol droplets manipulated with holographic optical tweezers, probing the shape relaxation dynamics following coalescence by simultaneously monitoring the intensity of elastic backscattered light (EBL) from the trapping laser beam (time resolution on the order of 100 ns) while recording high frame rate camera images (time resolution <10 μs). The goals of this work are to: resolve the dynamics of droplet coalescence in holographic optical traps; assign the origin of key features in the time-dependent EBL intensity; and validate the use of the EBL alone to precisely determine droplet surface tension and viscosity. For low viscosity droplets, two sequential processes are evident: binary coalescence first results from the overlap of the optical traps on the time scale of microseconds followed by the recapture of the composite droplet in an optical trap on the time scale of milliseconds. As droplet viscosity increases, the relaxation in droplet shape eventually occurs on the same time scale as recapture, resulting in a convoluted evolution of the EBL intensity that inhibits quantitative determination of the relaxation time scale. Droplet coalescence was simulated using a computational framework to validate both experimental approaches. The results indicate that time-dependent monitoring of droplet shape from the EBL intensity allows for robust determination of properties such as surface tension and viscosity. Finally, the potential of high frame rate imaging to examine the coalescence of dissimilar viscosity droplets is discussed.

Full‐field deformation measurements during seismic loading of masonry buildings

Summary This article demonstrates the potential of the digital image correlation (DIC) method to provide accurate full-field deformation measurements and successfully monitor the development of damage during seismic excitation of a partially grouted reinforced masonry building. The building was subjected to a sequence of earthquake ground motion records using the Large High Performance Outdoor Shake Table at the University of California, San Diego. The DIC setup was capable of measuring surface deformations of the single-story building with high frame rate cameras located at a distance greater than 50 ft away. The accuracy of the measurements was assessed with data obtained using mounted displacement transducers. The full-field deformation data collected by the DIC system was capable to detect strain localization patterns associated with the onset of wall cracking before it could be shown by the displacement sensor data or by post mortem visual inspection. The research findings reported herein demonstrate, for the first time to the authors' best knowledge, the potential of in situ monitoring of actual structures for damage induced by non-stationary loading profiles using optical metrology. Copyright © 2016 John Wiley & Sons, Ltd.

PWE-049 Small-Bowel Capsule Endoscopy with 360° Panoramic-View: Results of The First Multicenter, Observational, Study

Introduction CapsoCam®SV (CapsoVision Inc, Saratoga, USA) is a new small bowel capsule (SBC) with “panoramic view”, wire-free technology, and a long-lasting battery life. It is equipped with 4 high-frame rate cameras resulting in a high number of acquired frames. In previous studies, CapsoCam®SV showed comparable operative and diagnostic performance with frontal view SBCs. 1,2 Methods First multicenter study to assess the performance of CapsoCam®SV1 and SV2. Between January 2011 and November 2015, all consecutive patients undergoing SBC with CapsoCam® in 4 Italian, 2 British, and 1 German Institution(s) were included. Findings were classified according to their clinical significance, in line with Saurin classification, as P0: low probability; P1: intermediate probability; P2: high probability. 3 We defined SBC as “positive” when at least one P2 finding was identified. Results We enrolled 172 patients (94 M; median age±SD: 68±17 years, range: 9–97 years). Of them, 142 were referred for obscure GI bleeding (32 overt/110 occult OGIB) and 28 for suspected (17) or established (2) Crohn’s disease (CD). Median battery life was 16.4 h (range 3.7–23.4 h). System failure occurred in 4 (2%) cases for technical problems; incomplete enteroscopy in 16/168 (9%), including two structuring disorders (i.e. stricturing CD & SB adenocarcinoma) with spontaneous capsule excretion and one stricturing SB carcinoid with capsule retrieval at time of surgery.The ampulla of Vater was clearly identified in 34% cases. The overall diagnostic yield (DY; rate of positive tests) was 41%; 43% in OGIB and 30% in suspected CD. In a per-lesion analysis, overall 560 findings were detected (P0: 55, P1: 253, P2: 252). Most lesions were located in the small bowel (448/560: 80%); 48% of them were P2. Interestingly, 95/560 (17%) and 17/560 (3%) lesions were detected in the upper and in the lower GI tract, 34 and 12 of them being classified as P2, respectively. Conclusion The first multicenter study conducted in the everyday clinical practice with CapsoCam®SV, and based on the largest series so far collected, showed that SBC with 360° panoramic-view is easy to use, reliable, and has comparable DY and safety profile to forward view SCE. References 1 Friedrich K, et al . J Gastroenterol Hepatol 2013; 28 (9):1496–501. 2 Pioche M, et al . Endoscopy 2014; 46 (6):479–84. 3 Saurin JC, et al . Endoscopy 2003; 35 (7):576–84. Disclosure of Interest None Declared