Spatiotemporal multiplexing and streaming of hologram data for full-color holographic video display

We propose a new approach to spatiotemporally multiplex sub-holograms and stream hologram data in parallel by using multiple spatial light modulators (SLMs) to increase the spatiotemporal resolution of holographic display system. With the proposed approach, we have achieved a spatiotemporal resolution of 4.5 × 10¹⁰ pixel/s, as compared with 1.89 × 10⁹ pixel/s of a single SLM. Each frame of computer-generated hologram video has a pixel count of 378 Mpixels and is divided into 288 sub-holograms, each of 1.31 Mpixels. During the playback of holographic video, these sub-holograms are spatiotemporally multiplexed and streamed in parallel to form the integrated hologram within 16.67 ms, which enables full-color holographic video display with a 10-in. diagonal at a hologram data frame rate of 60 frames per second (fps). New SLM devices with higher spatiotemporal resolution need to be developed in order to meet the data bandwidth requirement of about 10¹²–10¹⁴ pixel/s for future 3D holographic displays.     

Three-dimensional bubbly flow measurement using PIV

The experimental flow visualization tool, Particle Image Velocimetry (PIV), is being extended to determine the velocity fields in three-dimensional, two-phase fluid flows. In the past few years, the technique has attracted quite a lot of interest. PIV enables fluid velocities across a region of a flow to be measured at a single instant in time in the whole volume (global) of interest. This instantaneous velocity profile of a given flow field is determined by digitally recording particle (microspheres or bubbles) images within the flow over multiple successive video frames and then conducting flow pattern identification and analysis of the data. This paper presents instantaneous velocity measurements in various three-dimensional, bubbly two-phase flow situations. This information is useful for developing or improving existing computer constitutive models that simulate this type of flow field. It is also useful for understanding the detailed structure of two-phase flows.     

Direct measurement of fluid velocity gradients at a wall by PIV image processing with stereo reconstruction

Velocity gradient is typically estimated in Particle Image Velocimetry (PIV) by differentiating a measured velocity field, which amplifies noise in the measured velocities. If gradients near a boundary are sought, such noise is usually greater than in bulk fluid, because of small tracer displacement, uncertainty in the effective positions of velocity vectors, intense deformation of tracer patterns, and laser reflection. We consider here a modified form of the Particle Image Distortion (PID) method todirectly calculate velocity gradients at a fixed wall, and refer it as “PIV/IG” (“Interface Gradiometry”). Results from synthetic 2D PIV images suggest our method achieves higher SNR and accuracy than velocity differentiation. Also, we have developed a procedure to reconstruct three-dimensional velocity gradient at a fixed wall the two non-zero components from PIV/IG data obtained in stereo views; these equations simplify considerably thanks to the no-slip condition. Experimental data from the bottom wall of turbulent open channel flow appear to suffer from a form of pixel locking. As with standard PIV, this underlines the importance of adequate tracer diameter in the images, sufficient seeding density, and of dynamic range of the camera sensor.     

PIV and LDA measurements of secondary flow in a meandering channel for overbank flow

Secondary flow in a compound meandering channel with straight floodplain banks for overbank was investigated by a visualization method and velocity measurement using three-component laser Doppler anemometor (LDA). The secondary flow in a cross section was visualized by the neutral buoyant tracer method with a submergible video camera. Secondary flow vectors in a cross section were obtained by using PIV software with captured frames from video source through PC and also by LDA measurements. From the comparison of the PIV and LDA results, it is found that PIV data show good agreement in quality with LDA measurements when the secondary flow is strong and stable as shown in this paper.     

Sub‐microsecond‐resolved multi‐speckle X‐ray photon correlation spectroscopy with a pixel array detector

Small‐angle X‐ray photon correlation spectroscopy (XPCS) measurements spanning delay times from 826 ns to 52.8 s were performed using a photon‐counting pixel array detector with a dynamic range of 0–3 (2 bits). Fine resolution and a wide dynamic range of time scales was achieved by combining two modes of operation of the detector: (i) continuous mode, where data acquisition and data readout are performed in parallel with a frame acquisition time of 19.36 µs, and (ii) burst mode, where 12 frames are acquired with frame integration times of either 2.56 µs frame^?1 or 826 ns frame^?1 followed by 3.49 ms or 1.16 ms, respectively, for readout. The applicability of the detector for performing multi‐speckle XPCS was demonstrated by measuring the Brownian dynamics of 10 nm‐radius gold and 57 nm‐radius silica colloids in water at room temperature. In addition, the capability of the detector to faithfully record one‐ and two‐photon counts was examined by comparing the statistical distribution of photon counts with expected probabilities from the negative binomial distribution. It was found that in burst mode the ratio of 2 s to 1 s is markedly smaller than predicted and that this is attributable to pixel‐response dead‐time.     

Sustained simultaneous high-speed imaging of scalar and velocity fields using a single laser

A high-speed technique that combines planar laser induced fluorescence (PLIF) detection of biacetyl and particle image velocimetry (PIV) for simultaneous imaging of scalar and velocity fields is demonstrated at a frame rate of 12 kHz for up to 32500 consecutive frames. A single diode-pumped, frequency-tripled Nd-YAG laser was used for excitation. Wavelength-separated recording was achieved for Mie scattering from silicone oil droplets with a CMOS camera and for the red-shifted fluorescence from biacetyl with an image-intensified CMOS camera. Interference between PIV and PLIF tracers was found to be negligible. Cross-talk between PIV and PLIF signals was low and a strategy to completely eliminate it was devised and is discussed. The signal-to-noise ratio is about 9 for single-shot scalar images. Example image sequences were recorded in an atmospheric pressure air jet at Re=2000. PACS 42.62.Fi; 33.50.Dq; 06.30.Gv; 06.60.Jn     

Analysis of jet entrainment mechanism in the transitional regime by time-resolved PIV

Abstract  

The entrainment mechanism in the near field of daisy-shaped and circular orifice jets have been investigated in the transitional regime using time-resolved 2D PIV measurements. The objective is to improve the knowledge from one previous investigation at initial Reynolds number of 800, based on the construction of a pseudo-time resolved PIV fields using the combination of non time-resolved PIV measurements and time-resolved visualizations (Nastase and Meslem J Vis 11(4):309–318, 2008). As expected in the previous work, the entrainment in the circular jet is correlated to the periodic Kelvin–Helmholtz (K–H) ring passing and the entrainment is produced in the braid region where the streamwise structures develop. In the daisy jet, we found that the entrainment rate is not correlated to the periodic K–H vortex passing. The observed small variation of the entrainment rate amplitude in the daisy jet could be related to the K–H dynamics. However, at the studied low Reynolds number the contribution of the K–H vortex on the daisy jet entrainment seems negligible comparing with the streamwise structures role. Furthermore, the real-time resolved measurements allow an indepth analysis of the role played by the K–H ring in the entrainment of circular jet. It is shown that the entrainment is not only produced in the braid region but is also present in the upstream part of the K–H ring. In the downstream part of the ring, the entrainment is dramatically reduced. This new observation opens a question which still has to be answered with time-resolved 3D PIV measurements. The question is “Whether the depression formed due to the ring passing or the streamwise structures rolled-up on the ring is responsible for entrainment at the upstream part of the ring?”     

Performance evaluation of an optical flow technique applied to particle image velocimetry using the VSJ Standard Images

A Dynamic Programming based Optical Flow technique has been applied to the Particle Image Velocimetry (PIV) problem. It has been used for the extraction of dense velocity fields in a planar section of a fluid flow illuminated by a thin laser light sheet. Two (in-plane) components of the velocity vectors can be recovered using a single camera and all three components can be recovered using two or three cameras. Quantitative performance tests have been carried out on calibrated synthetic image sequences from the PIV Standard Project of the Visualization Society of Japan (VSJ). Results are presented for the 2D flow based sequences (STD01 to STD08 Standard Images) and the 3D flow based sequences (STD301, STD302, STD331 and STD337 Standard Images). The RMS error is within the 2–3% range and within the 4–8% range for recovery of the two-component and the three-component velocity vectors respectively.     

Planar velocity visualization in high-speed wedge flow using Doppler Picture Velocimetry (DPV) compared with Particle Image Velocimetry (PIV)

A technique for visualizing a velocity field in an entire plane has been developed by taking ‘Doppler Pictures’ using Michelson interferometry. With the Doppler Picture Velocimetry (DPV), information about the instantaneous and local velocities of tracers passing through a light sheet is available. The technique for taking and processing the Doppler pictures has been improved recently and the state-of-the-art of the DPV method will be described with an application in high-speed fluid flows showing the velocity distribution in a light sheet plane crossing a supersonic wedge flow generated in the high-energy shock tunnel STB of ISL. A comparison with Particle Image Velocimetry (PIV) velocity visualizations is also presented.     

Texton-based super-resolution for achieving high spatiotemporal resolution in hybrid camera system

Many super-resolution methods have been proposed to enhance the spatial resolution of images by using iteration and multiple input images. In a previous paper, we proposed the example-based super-resolution method to enhance an image through pixel-based texton substitution to reduce the computational cost. In this method, however, we only considered the enhancement of a texture image. In this study, we modified this texton substitution method for a hybrid camera to reduce the required bandwidth of a high-resolution video camera. We applied our algorithm to pairs of high- and low-spatiotemporal-resolution videos, which were synthesized to simulate a hybrid camera. The result showed that the fine detail of the low-resolution video can be reproduced compared with bicubic interpolation and the required bandwidth could be reduced to about 1/5 in a video camera. It was also shown that the peak signal-to-noise ratios (PSNRs) of the images improved by about 6 dB in a trained frame and by 1.0–1.5 dB in a test frame, as determined by comparison with the processed image using bicubic interpolation, and the average PSNRs were higher than those obtained by the well-known Freeman’s patch-based super-resolution method. Compared with that of the Freeman’s patch-based super-resolution method, the computational time of our method was reduced to almost 1/10.     

A real-time video encoded particle imaging tracking technique for velocity measurement

A real-time video encoded particle imaging tracking technique (VPIT) for velocity measurement has been developed. It can currently capture images of a seeded particle flow field at up to a video rate of 25 pictures per second. The method as shown in this paper is suitable for measuring a slow sparsely seeded flow. A VPIT image presents a triplet image pattern. The image has been encoded into a single video frame with the time history of three events. This is achieved by synchronising the video (CCIR) signal from a CCD (charge coupled device) camera, operating in frame integration mode with a suitable light source. The principle of VPIT demonstrates how the direction and the magnitude of the velocity can be recorded for a sequence or track of particles. The VPIT triplet images resolve several common difficulties associated with the application of PIV. Firstly, the time history of the laser pulse can be ‘labeled’ on an individual particle image. Secondly, there is no velocity direction ambiguity in the VPIT image. Thirdly, it is possible to extract the acceleration of the particle from a single VPIT frame. Finally, for a sequence of captured frames, the problems of particle path tracking are simplified, because each VPIT image has a video encoded time sequence ‘labelled’ on it.     

Vortical dynamics in the wake of water strider locomotion

Abstract  

Previous studies reported that the hydrodynamic propulsion of the water strider also results from transferring momentum to the underlying fluid through hemispherical dipolar vortices shed by its driving legs. However, there are no accuracy experimental measurements of these vortical structures to prove the mechanics of vortical propulsion. Here, we reveal the vortical structures by reporting the simultaneous measurements of the water strider’s motion and the fluid velocity field with the high-speed PIV, and proposing a new method of calculating the vortex kinetic energy and vortex momentum. We found that the asymmetrical vortical structure in each dipolar vortex, generated by one driving stroke, propels the water strider forward, and the outer elliptic vortex is weaker than the inner circular vortex. The movement of the dipolar vortex is divided into two stages: (1) translating backward and (2) return curving. In this way, the water strider obtains the maximum velocity with minimal consumption of energy. The fluid vortical momentum, generated by the driving stroke, accounts for about 64–90% of the water strider’s momentum.     

Video Summarization Based on Mutual Information and Entropy Sliding Window Method

This paper proposes a video summarization algorithm called the Mutual Information and Entropy based adaptive Sliding Window (MIESW) method, which is specifically for the static summary of gesture videos. Considering that gesture videos usually have uncertain transition postures and unclear movement boundaries or inexplicable frames, we propose a three-step method where the first step involves browsing a video, the second step applies the MIESW method to select candidate key frames, and the third step removes most redundant key frames. In detail, the first step is to convert the video into a sequence of frames and adjust the size of the frames. In the second step, a key frame extraction algorithm named MIESW is executed. The inter-frame mutual information value is used as a metric to adaptively adjust the size of the sliding window to group similar content of the video. Then, based on the entropy value of the frame and the average mutual information value of the frame group, the threshold method is applied to optimize the grouping, and the key frames are extracted. In the third step, speeded up robust features (SURF) analysis is performed to eliminate redundant frames in these candidate key frames. The calculation of Precision, Recall, and Fmeasure are optimized from the perspective of practicality and feasibility. Experiments demonstrate that key frames extracted using our method provide high-quality video summaries and basically cover the main content of the gesture video.     

A concept of the design of a phase-meter radionavigation system for control over high-speed objects

In the present work, a concept of the design of a navigation system for high-speed ground transport based on the phase-meter method is substantiated. It is demonstrated that the system provides high accuracy of positioning of a high-speed object (with an error of ∼10–20 cm for speeds up to 500 km/h and linear object dimensions of ∼100 m) sufficient for control over a linear engine and allows measuring information from sensors to be processed and control commands for actuators to be generated in real time. Requirements to the frequency stability of reference and mobile microwave generators are determined. A built-in subsystem of diagnostics of radionavigation system efficiency is suggested, which increases reliability of the control system for high-speed ground transport and thereby safety of high-speed transportations. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 81–87, July, 2007.     

CW laser-induced fluorescence of toluene for time-resolved imaging of gaseous flows

A laser-induced fluorescence diagnostic is presented for high-speed measurements in gaseous flows. The technique employs a toluene tracer excited at 266 nm by a cavity-doubled 532 nm diode-pumped 5.5 W CW laser. The high power (600 mW) of UV light produced by cavity doubling, together with the high fluorescence yield of toluene, yields strong signal levels needed for high-speed recording. Fluctuation detection limits for tracer mole fraction were investigated by applying the diagnostic to an atmospheric temperature and pressure nitrogen jet. For single-point measurements with a photomultiplier tube, the detection limit for fluctuations in the toluene mole fraction was 0.028%, achieved with 430 mW of laser power and 8.5 kHz bandwidth for a 1×0.4×0.4 mm collection volume. Line (1-D) imaging with a kinetic-readout camera (512 pixels/row) achieved a detection limit of 0.23% with 440 mW of laser power, 9.7 kHz frame rate, and 0.3×0.2×0.4 mm collection volume per pixel, while planar (2-D) imaging with a 512×512 pixel intensified camera achieved a detection limit of 0.88% with 205 mW of laser power, 100 μs exposure time, and 0.4×0.4×0.4 mm volume per pixel. Line and planar imaging were applied to a turbulent jet with Re of about 10000.     

Measurements-based Moving Target Detection in Quantum Video

A method to detect a moving target in multi-channel quantum video is proposed based on multiple measurements on the video strip. The proposed method is capable of detecting the location of the moving target in each frame of the quantum video thereby ensuring that the motion trail of the object is easily and efficiently retrieved. Three experiments, i.e. moving target detection (MTD) of a pixel, MTD of an object in complex shape, and MTD of a pixel whose color is conterminous with that of its background, are implemented to demonstrate the feasibility of the proposal. This study presents a modest attempt to focus on the moving target detection and its applications in quantum video.     

A new super-resolution PIV accelerated by characteristic pixel selection

A new high-speed super-resolution PIV was proposed using characteristic pixel selection to accelerate the successive abandonment (SA) with recursive window subdivision. The performance and applicability of the proposed PIV were evaluated. In the SA calculation with the characteristic pixel selection, 1000 candidates are narrowed down to only one at over 50 % of the measurement points, and the number of error vectors is reduced because the difference between the cumulative intensities of a correct candidate and of other ones becomes clear due to the characteristics of selected pixels. In all recursive processes, error checks are carefully performed using the summation of the distribution of the cumulative intensity difference distribution, which is suitable for the SA method. In a comparison of the time per velocity vector, the present super-resolution PIV was shown to be 10 times faster than the former ordinary resolution PIV. Another feature of the present super-resolution PIV is that the velocity vectors are obtained in the region very close to the image boundaries and masked regions by using the recursive algorithm.     

Cavitation under spherical focusing of acoustic pulses

The early stage of the dynamics of interacting cavitation bubbles in a transmitted spherically focused pulsed wave consisting of compression and rarefaction phases is studied. The cavitation is investigated away from the liquid boundaries for negative pressures up to −42 MPa with a decrease rate of −40 MPa/μs by high-speed microscopic filming (100 million frames per second and a spatial resolution of 5–50μm/pixel) and pressure measurements. It is demonstrated that, according to the kinematics of size variation, the bubbles are separated into two fractions: expanding and collapsing ones. Experimental data provide grounds to assume that the formation of a two-fraction bubble cluster occurs on account of different threshold values of pressure in the rarefaction wave for two characteristic sizes of nuclei, namely, micronuclei (d _I < 10μm) and nanonuclei (“bubstons,” d _II ∼ 1 nm), which become detectable only when the rarefaction wave amplitude exceeds the critical one. Pulsed compression of small bubbles in the process of transformation of a rarefaction wave into a compression wave occurs under the effect of a cluster’s internal pressure up to 20 MPa and proceeds with the conservation of the spherical shape of the second-fraction bubbles. It is demonstrated that the velocity of the center of mass of a bubble reaches its peak value close to the moment of bubble collapse. The translational and radial dynamics of a bubble are studied in a numerical experiment using the Rayleigh-Plesset equation and taking into account the viscous force and the pressure gradient. The results of measuring the translational shift may be useful for estimating the minimum bubble radius by comparing the numerical results with the experiment.     

A mixed framework for transform domain Wyner–Ziv video coding

This paper presents a mixed framework based on an efficient intra key frame coding and an improved side information (SI) generation scheme in transform domain Wyner–Ziv (WZ) video coding. The performance of the WZ video coding strongly depends on the quality of the SI. The SI can be generated from the decoded key frames resulted from intra key frame video coding. The better the decoded key frames are the better would be the SI generation. In this paper, a Burrows–Wheeler transform (BWT) based intra-frame video coding is proposed to generate improved decoded key frames. Furthermore, an improved SI generation scheme with multilayer perceptron (MLP) is proposed. Comparative analysis with other standard techniques of WZ video coding reveals that the proposed scheme has better standing as compared to its counterparts in terms of both coding efficiency and improved perceptual quality.