Accurate Shape Measurement Research Articles

Mechanical Characterization of Liposomes and Extracellular Vesicles, a Protocol.

Both natural as well as artificial vesicles are of tremendous interest in biology and nanomedicine. Small vesicles (<200 nm) perform essential functions in cell biology and artificial vesicles (liposomes) are used as drug delivery vehicles. Atomic Force Microscopy (AFM) is a powerful technique to study the structural properties of these vesicles. AFM is a well-established technique for imaging at nanometer resolution and for mechanical measurements under physiological conditions. Here, we describe the procedure of AFM imaging and force spectroscopy on small vesicles. We discuss how to image vesicles with minimal structural disturbance, and how to analyze the data for accurate size and shape measurements. In addition, we describe the procedure for performing nanoindentations on vesicles and the subsequent data analysis including mechanical models used for data interpretation.

Investigation of Phase Pattern Modulation for Digital Fringe Projection Profilometry

Abstract The fringe projection profilometry with sinusoidal patterns based on phase-shifting algorithms is commonly distorted by the nonlinear intensity response of commercial projector. In order to solve this issue, sinusoidal width modulation is presented to generate binary sinusoidal patterns for defocusing the projection. However, the residual errors in the phase maps are usually notable for highly accurate three-dimensional shape measurements. In this paper, we propose the fringe patterns of the sinusoidal, square, and triangular periodic waveforms with seven-step phase-shifting algorithm to further improve the accuracy of three-dimensional profile reconstruction. The absolute phase values are calculated by using quality guided path unwrapping. We learn that by properly selecting fringe patterns according to the target shape, the undesired harmonics of the measured surface have negligible effect on the phase values. The experiments are presented to verify the imaging performances of three fringe patterns for different testing targets. The triangular fringe patterns are suitable for the shape measurements of complex targets with curved surfaces. The results provide a great possibility for high-accuracy shape measurement technique with wider measuring depth range.

Flexible gamma calculation algorithm based on probability distribution function in digital fringe projection system.

The gamma effect of phase-measuring profilometry systems yields nonlinear errors, which will substantially reduce the 3D shape measurement accuracy. Here, a robust and flexible gamma correction method based on the probability distribution function (PDF) of the wrapped phase is presented. First, a series of PDF curves are generated from the simulated wrapped phase distributions with different gamma values. Second, an experimental PDF curve will be produced after obtaining the wrapped phase from the captured three-step phase-shift fringe images. Then, a correlation procedure will be used to find the most similar PDF curve from the simulated PDF curves, and the gamma value of the matched PDF curve is that of the current system. Note that the gamma value detected by this method will be smaller than the true value due to the defocusing effect of the projection system with a large aperture. Therefore, an improved PDF-based algorithm, which projects two sets of three-step phase-shifting sinusoidal fringe patterns with different pre-coded gamma values and produces two PDF curves, is also added. Then after one more correlation procedure, a more accurate systematic gamma value could be calculated. It does not need large-step phase-shift images and 2×3 fringe images are quite enough. The experimental results show that the technique is very fast, easy to use and quite accurate.

Real-time 3D shape measurement using 3LCD projection and deep machine learning.

For 3D imaging and shape measurement, simultaneously achieving real-time and high-accuracy performance remains a challenging task in practice. In this paper, a fringe-projection-based 3D imaging and shape measurement technique using a three-chip liquid-crystal-display (3LCD) projector and a deep machine learning scheme is presented. By encoding three phase-shifted fringe patterns into the red, green, and blue (RGB) channels of a color image and controlling the 3LCD projector to project the RGB channels individually, the technique can synchronize the projector and the camera to capture the required fringe images at a fast speed. In the meantime, the 3D imaging and shape measurement accuracy is dramatically improved by introducing a novel phase determination approach built on a fully connected deep neural network (DNN) learning model. The proposed system allows performing 3D imaging and shape measurement of multiple complex objects at a real-time speed of 25.6fps with relative accuracy of 0.012%. Experiments have shown great promise for advancing scientific and engineering applications.

A flexible and easy-to-implement single-camera microscopic 3D digital image correlation technique

We propose a novel, flexible and easy-to-implement single-camera microscopic three-dimensional digital image correlation (3D-DIC) technique for accurate full-field shape, motion and deformation measurements at the microscale. The established microscopic 3D-DIC system comprises a single 3CCD color camera, a high-magnification zoom lens, and a specially designed color separation device using a beam splitter, two optical bandpass filters and three plane mirrors. To perform accurate stereo measurement, color images of a test sample surface are recorded by the 3CCD camera, which observes the test sample via the microscopic imaging system from two different optical paths with the aid of the color separation device. The recorded color images can be subsequently separated to red and green channel sub-images which constitute stereo pairs corresponding to different perspectives. The separated stereo pairs can be subsequently analyzed using regular 3D-DIC to extract full-field 3D shape and deformation of the test object surface. The method was first validated by a series of benchmark tests, involving the 3D shape reconstruction of steel balls with different diameters, in-plane and out-of-plane translation tests. Surface 3D deformation measurement of a planar acrylic plate with micro-features was also performed to show the practicality of the proposed method. This method provides new simple and practical avenues for performing shape and deformation measurement at microscale, showing great potential in both material testing and bio-tissue characterization.

Optimal pulse width modulation technique combined with stair phase-coding method for absolute phase retrieval with projector defocusing

The accurate three-dimensional shape measurement of a complex surface is significantly important in industrial testing. However, three-dimensional profilometry by conventional sinusoidal fringe projection using a phase-shifting algorithm performs suboptimally because of the nonlinear intensity response of projectors. To overcome this problem, the present paper proposes using a combined optimizing sinusoidal pulse width modulation (SPWM) technique and stair phase-coding approach to obtain the unwrapped phase. Properly optimizing SPWM with a small degree of a defocusing projector to generate sinusoidal fringe patterns can overcome the undesired harmonics and nonlinear gamma effect. Two groups of four-step phase-shifting fringe patterns are used. One group of the stripes contains four sinusoidal patterns generated by the SPWM technique, which is used to determine the wrapped phase. The other group of stripes contains four sinusoidal patterns with the codeword embedded into the stair phase, whose stair changes are perfectly aligned with the 2π discontinuities of the sinusoidal fringe phase, which is used to determine the fringe order for the phase unwrapping. Moreover, for the defocusing projection, because the frequency of the phase-coding fringe increases, the fringe order decision becomes less reliable. Thus, a self-correction phase unwrapping method is applied for phase retrieval. Experiments were conducted to verify the performance of the proposed method.

A Structured Light RGB-D Camera System for Accurate Depth Measurement

The ability to reliably measure the depth of the object surface is very important in a range of high-value industries. With the development of 3D vision techniques, RGB-D cameras have been widely used to perform the 6D pose estimation of target objects for a robotic manipulator. Many applications require accurate shape measurements of the objects for 3D template matching. In this work, we develop an RGB-D camera based on the structured light technique with gray-code coding. The intrinsic and extrinsic parameters of the camera system are determined by a calibration process. 3D reconstruction of the object surface is based on the ray triangulation principle. We construct an RGB-D sensing system with an industrial camera and a digital light projector. In the experiments, real-world objects are used to test the feasibility of the proposed technique. The evaluation carried out using planar objects has demonstrated the accuracy of our RGB-D depth measurement system.

5D hyperspectral imaging: fast and accurate measurement of surface shape and spectral characteristics using structured light.

Measuring the shape (coordinates x, y, z ) and spectral characteristics (wavelength-dependent reflectance R (λi)) of macroscopic objects as a function of time (t) is of great interest in areas such as medical imaging, precision agriculture, or optical sorting. Here, we present an approach that allows to determine all these quantities with high resolution and accuracy, enabling measurement in five dimensions. We call this approach 5D hyperspectral imaging. We describe the design and implementation of a 5D sensor operating in the visible to near-infrared spectral range, which provides excellent spatial and spectral resolution, great depth accuracy, and high frame rates. The results of various experiments strongly indicate the great benefit of the new technology.

Size and Shape Distribution of Bipyramidal TiCh Nanoparticles by Transmission Electron Microscopy - an Inter-Laboratory Comparison

Extraction of true, 3D shape (and size) of non-spherical nanoparticles (NPs) is associated with errors by conventional 2D electron microscopy using projection images. Significant efforts within the ISO technical committee TC 229 ‘Nanotechnologies’ are aimed at establishing accurate TEM and SEM measurement of NP size and shape as robust, standard procedures. Study groups have been organizing inter-laboratory comparisons on well-selected NP systems according to the market needs, such as aggregated titania nano-powder for which size and shape distribution of primary crystallites of irregular shape must be measured accurately. To be noticed is e. g. the fact that the measurement procedure allows only manual selection of the particles clearly distinguishable for analysis as well as manual definition of the contour of the imaged NPs. An inter-laboratory exercise on titania NPs (pure anatase, grown by hydrothermal synthesis) of well-defined non-spherical shape, i.e. bipyramidal has been recently started within ISO/TC 229 under similar conditions as for the irregular shaped titania. Overlapped particles were allowed to be considered, as long as they are clearly distinguishable. One decisive NP selection criterion was to analyze only those NPs with a roundness value below 0.7, i.e. the NPs laying on the support foil and, hence, with projection areas clearly deviating from perfect circles (R=1). The overall evaluation (for 15 labs) of the size descriptors (area, Feret, minFeret, perimeter) and shape descriptors (aspect ratio, roundness, compactness, extent) by analysis of variance is just to be finished and included in ISO/WD 21363 Nanotechnologies -- Protocol for particle size distribution by transmission electron microscopy.

Analytical noise bias correction for weak lensing shear analysis with ERA

Highly precise weak lensing shear measurement is required for statistical weak gravitational lensing analysis such as cosmic shear measurement to achieve severe constraint on the cosmological parameters. For this purpose, the accurate shape measurement of background galaxies is absolutely important in which any systematic error in the measurement should be carefully corrected. One of the main systematic error comes from photon noise which is Poisson noise of flux from the atmosphere(noise bias). We investigate how the photon noise makes a systematic error in shear measurement within the framework of ERA method we developed in earlier papers and gives a practical correction method. The method is tested by simulations with real galaxy images with various conditions and it is confirmed that it can correct $80 \sim 90\%$ of the noise bias except for galaxies with very low signal to noise ratio.

Electron beam-based metrology after CMOS.

The magnitudes of the challenges facing electron-based metrology for post-CMOS technology are reviewed. Directed selfassembly, nanophotonics/plasmonics, and resistive switches and selectors, are examined as exemplars of important post-CMOS technologies. Materials, devices, and architectures emerging from these technologies pose new metrology requirements: defect detection, possibly subsurface, in soft materials, accurate measurement of size, shape, and roughness of structures for nanophotonic devices, contamination-free measurement of surface-sensitive structures, and identification of subtle structural, chemical, or electronic changes of state associated with switching in non-volatile memory elements. Electron-beam techniques are examined in the light of these emerging requirements. The strong electron-matter interaction provides measurable signal from small sample features, rendering electron-beam methods more suitable than most for nanometer-scale metrology, but as is to be expected, solutions to many of the measurement challenges are yet to be demonstrated. The seeds of possible solutions are identified when they are available.

3D bubble reconstruction using multiple cameras and space carving method

An accurate measurement of bubble shape and size has a significant value in understanding the behavior of bubbles that exist in many engineering applications. Past studies usually use one or two cameras to estimate bubble volume, surface area, among other parameters. The 3D bubble shape and rotation angle are generally not available in these studies. To overcome this challenge and obtain more detailed information of individual bubbles, a 3D imaging system consisting of four high-speed cameras is developed in this paper, and the space carving method is used to reconstruct the 3D bubble shape based on the recorded high-speed images from different view angles. The proposed method can reconstruct the bubble surface with minimal assumptions. A benchmarking test is performed in a 3 cm × 1 cm rectangular channel with stagnant water. The results show that the newly proposed method can measure the bubble volume with an error of less than 2% compared with the syringe reading. The conventional two-camera system has an error around 10%. The one-camera system has an error greater than 25%. The visualization of a 3D bubble rising demonstrates the wall influence on bubble rotation angle and aspect ratio. This also explains the large error that exists in the single camera measurement.

The galaxy–subhalo connection in low-redshift galaxy clusters from weak gravitational lensing

We measure the gravitational lensing signal around satellite galaxies in a sample of galaxy clusters at $z<0.15$ by combining high-quality imaging data from the Canada-France-Hawaii Telescope with a large sample of spectroscopically-confirmed cluster members. We use extensive image simulations to assess the accuracy of shape measurements of faint, background sources in the vicinity of bright satellite galaxies. We find a small but significant bias, as light from the lenses makes the shapes of background galaxies appear radially aligned with the lens. We account for this bias by applying a correction that depends on both lens size and magnitude. We also correct for contamination of the source sample by cluster members. We use a physically-motivated definition of subhalo mass, namely the mass bound to the subhalo, $m_\mathrm{bg}$, similar to definitions used by common subhalo finders in numerical simulations. Binning the satellites by stellar mass we provide a direct measurement of the subhalo-to-stellar-mass relation, $\log m_\mathrm{bg}/\mathrm{M}_\odot = (11.54\pm0.05) + (0.95\pm0.10)\log[m_\star/(2\times10^{10}\mathrm{M}_\odot)]$. This best-fitting relation implies that, at a stellar mass $m_\star\sim3\times10^{10}\,\mathrm{M}_\odot$, subhalo masses are roughly 50 per cent of those of central galaxies, and this fraction decreases at higher stellar masses. We find some evidence for a sharp change in the total-to-stellar mass ratio around the clusters' scale radius, which could be interpreted as galaxies within the scale radius having suffered more strongly from tidal stripping, but remain cautious regarding this interpretation.

Calibration of colour gradient bias in shear measurement using HST/CANDELS data

Accurate shape measurements are essential to infer cosmological parameters from large area weak gravitational lensing studies. The compact diffraction-limited point-spread function (PSF) in space-based observations is greatly beneficial, but its chromaticity for a broad band observation can lead to new subtle effects that could hitherto be ignored: the PSF of a galaxy is no longer uniquely defined and spatial variations in the colours of galaxies result in biases in the inferred lensing signal. Taking Euclid as a reference, we show that this colourgradient bias (CG bias) can be quantified with high accuracy using available multi-colour Hubble Space Telescope (HST) data. In particular we study how noise in the HST observations might impact such measurements and find this to be negligible. We determine the CG bias using HST observations in the F606W and F814W filters and observe a correlation with the colour, in line with expectations, whereas the dependence with redshift is weak. The biases for individual galaxies are generally well below 1%, which may be reduced further using morphological information from the Euclid data. Our results demonstrate that CG bias should not be ignored, but it is possible to determine its amplitude with sufficient precision, so that it will not significantly bias the weak lensing measurements using Euclid data.

Accurate shape measurement of focusing microstructures in Fourier digital holographic microscopy.

This paper proposes a measurement method of focusing objects with a high gradient shape of a small and large radius of curvature. The measurements are carried out on a Fourier digital holographic microscope with optimized illumination conditions maximizing the usage of the system's numerical aperture. The obtained fringe patterns are the result of interference of deformed spherical object and spherical reference waves. The key elements of the method are the aberration compensation and calibration procedures. They provide accurate reconstruction of the object wave and determination of the focus position of the sample. The shape is calculated in two steps. First, the object wave is reconstructed at the plane of the object focus using single or multiframe phase extraction algorithm and the specialized propagation method. The step includes compensation for spherical aberration. In the second step, the sample shape is computed with the local ray approximation approach. The proposed method is experimentally validated with measurements of challenging, high gradient shapes (convex, concave) of different radiuses of curvature.

3D shape, deformation, and vibration measurements using infrared Kinect sensors and digital image correlation.

Consumer-grade red-green-blue and depth (RGB-D) sensors, such as the Microsoft Kinect and the Asus Xtion, are attractive devices due to their low cost and robustness for real-time sensing of depth information. These devices provide the depth information by detecting the correspondences between the captured infrared (IR) image and the initial image sent to the IR projector, and their essential limitation is the low accuracy of 3D shape reconstruction. In this paper, an effective technique that employs the Kinect sensors for accurate 3D shape, deformation, and vibration measurements is introduced. The technique involves using the RGB-D sensors, an accurate camera calibration scheme, and area- and feature-based image-matching algorithms. The IR speckle pattern projected from the Kinect projector considerably facilitates the digital image correlation analysis in the regions of interest with enhanced accuracy. A number of experiments have been carried out to demonstrate the validity and effectiveness of the proposed technique and approach. It is shown that the technique can yield measurement accuracy at the 10μm level for a typical field of view. The real-time capturing speed of 30 frames per second makes the proposed technique suitable for certain motion and vibration measurements, such as non-contact monitoring of respiration and heartbeat rates.

The Complete Calibration of the Color–Redshift Relation (C3R2) Survey: Survey Overview and Data Release 1

Abstract A key goal of the Stage IV dark energy experiments Euclid, LSST, and WFIRST is to measure the growth of structure with cosmic time from weak lensing analysis over large regions of the sky. Weak lensing cosmology will be challenging: in addition to highly accurate galaxy shape measurements, statistically robust and accurate photometric redshift (photo-z) estimates for billions of faint galaxies will be needed in order to reconstruct the three-dimensional matter distribution. Here we present an overview of and initial results from the Complete Calibration of the Color–Redshift Relation (C3R2) survey, which is designed specifically to calibrate the empirical galaxy color–redshift relation to the Euclid depth. These redshifts will also be important for the calibrations of LSST and WFIRST. The C3R2 survey is obtaining multiplexed observations with Keck (DEIMOS, LRIS, and MOSFIRE), the Gran Telescopio Canarias (GTC; OSIRIS), and the Very Large Telescope (VLT; FORS2 and KMOS) of a targeted sample of galaxies that are most important for the redshift calibration. We focus spectroscopic efforts on undersampled regions of galaxy color space identified in previous work in order to minimize the number of spectroscopic redshifts needed to map the color–redshift relation to the required accuracy. We present the C3R2 survey strategy and initial results, including the 1283 high-confidence redshifts obtained in the 2016A semester and released as Data Release 1.

Accurate particle speed prediction by improved particle speed measurement and 3-dimensional particle size and shape characterization technique

Accurate particle mass and velocity measurement is needed for interpreting test results in erosion tests of materials and coatings. The impact and damage of a surface is influenced by the kinetic energy of a particle, i.e. particle mass and velocity. Particle mass is usually determined with optical methods, e.g. laser light scattering, and velocity by the double disk (DD) method. In this article we present two novel techniques, which allow a more accurate measurement of mass, velocity and shape, and we later compare the experimentally obtained flow velocities of particles with a simulation that also includes the particle's shape parameter, known as sphericity. Mass and sphericity are obtained from 3-dimensional data with an industrial X-ray computed tomography (CT) scanner. CT data can be used to accurately determine the volume-basis median of the particles (using the volume-equivalent particle diameter). Velocity is measured with a fast 2-dimensional particle imaging method using a pulsed LED. Good agreement of the measured and simulated particle velocity was found when including the sphericity from CT results. 2-dimensional optical particle size measurements in the jet of an erosion rig are compared with detailed 3-dimensional CT measurements and a low angle laser light scattering (LALLS) measurement system for six different samples of particles. It is shown that the particle volume or mass is usually overestimated by 16–22% when using 2-dimensional methods or LALLS. For CT allows additionally the surface-equivalent diameter to be calculated by using 2-dimensional projections of each particle, these results can be used to correct particle diameters measured with the particle imaging method using a pulsed LED.

A study of the sensitivity of shape measurements to the input parameters of weak-lensing image simulations

Improvements in the accuracy of shape measurements are essential to exploit the statistical power of planned imaging surveys that aim to constrain cosmological parameters using weak lensing by large-scale structure. Although a range of tests can be performed using the measurements, the performance of the algorithm can only be quantified using simulated images. This yields, however, only meaningful results if the simulated images resemble the real observations sufficiently well. In this paper we explore the sensitivity of the multiplicative bias to the input parameters of Euclid-like image simulations.We find that algorithms will need to account for the local density of sources. In particular the impact of galaxies below the detection limit warrants further study, because magnification changes their number density, resulting in correlations between the lensing signal and multiplicative bias. Although achieving sub-percent accuracy will require further study, we estimate that sufficient archival Hubble Space Telescope data are available to create realistic populations of galaxies.

Interferometric measurement of surface shape by wavelength tuning suppressing random intensity error.

In this research, the susceptibility of the phase-shifting algorithms to the random intensity error is formulated and estimated. The susceptibility of the random intensity error of conventional windowed phase-shifting algorithms is discussed, and the 7N-6 phase-shifting algorithm is developed to minimize the random intensity error using the characteristic polynomial theory. Finally, the surface shape of the transparent wedge plate is measured using a wavelength-tuning Fizeau interferometer and the 7N-6 algorithm. The experimental results indicate that the surface shape measurement accuracy for the transparent plate is 2.5 nm.