Defocused Images Research Articles

Quantitative high resolution electron microscopy image matching applied to the strontium titanate Σ3(112) grain boundary

Quantitative image matching has been employed in order to compare experimentally observed grain boundary structure to predicted model structures for the strontium titanate (SrTiO3) Σ3(112) grain boundary. Initially, quantitative image matching of image regions containing bulk crystal were used to determine the specimen and microscope parameters, including specimen thickness and tilt, and image defocus. Using the fitted values for thickness and defocus, images have been simulated from two proposed model structures of the SrTiO3 Σ3(112) grain boundary and quantitatively matched to experimental images.

The random-model method enables ab initio 3D reconstruction of asymmetric particles and determination of particle symmetry

Model-based, 3D reconstruction techniques depend on reliable starting models. We present an extension of the random-model method (RMM) that allows the ab initio generation of suitable starting models directly from un-averaged, experimental images of asymmetric or symmetric particles. Therefore, the asymmetric RMM can also be used to determine point-group symmetry. The procedure is facilitated by the use of (a) variable angular step-sizes during iterative origin and orientation searches, (b) high numbers of particle images, and (c) highly defocused images. The method is inhibited by mixed-handedness orientation assignments and by particles with inconspicuous features. For symmetric particles, symmetric RMMs can overcome these deficiencies.

2P1-G01 撮像領域を考慮した単眼カメラ画像のボケ量に基づく距離計測

In this paper. we propose and implement an 3D measurement system by using defocus images obtained from a single camera. Depth from Defocus (DFD) is one of methods to estimate depth information from a pair of two defocus images. In former researches, target object to be measured must be inside between the two images. We propose an algorithm to overcome the limitation, and have implemented the system by a high-speed camera and telecentric lens. We verified the efficiency of the proposed system by some experiments.

Detection and estimation of defocus in natural images

Detection and estimation of defocus in natural images

Zernike Phase Plate Cryoelectron Microscopy Facilitates Single Particle Analysis of Unstained Asymmetric Protein Complexes

Single particle reconstruction from cryoelectron microscopy images, though emerging as a powerful means in structural biology, is faced with challenges as applied to asymmetric proteins smaller than megadaltons due to low contrast. Zernike phase plate can improve the contrast by restoring the microscope contrast transfer function. Here, by exploiting simulated Zernike and conventional defocused cryoelectron microscope images with noise characteristics comparable to those of experimental data, we quantified the efficiencies of the steps in single particle analysis of ice-embedded RNA polymerase II (500 kDa), transferrin receptor complex (290 kDa), and T7 RNA polymerase lysozyme (100 kDa). Our results show Zernike phase plate imaging is more effective as to particle identification and also sorting of orientations, conformations, and compositions. Moreover, our analysis on image alignment indicates that Zernike phase plate can, in principle, reduce the number of particles required to attain near atomic resolution by 10-100 fold for proteins between 100 kDa and 500 kDa.

撮像領域を考慮した単眼カメラ画像のボケ量に基づく距離計測系

撮像領域を考慮した単眼カメラ画像のボケ量に基づく距離計測系

Estimating Moving Targets Behind Reinforced Walls Using Radar

We consider the estimation of moving targets located behind concrete walls reinforced with metallic bars, using radar measurements. The periodic structure of the rebar severely attenuates and distorts transmitted waveforms, which produces defocused images with ghost target estimates. We apply beamforming to estimate permittivity and thickness of the wall and number and position of the targets. The proposed solution is based on accurate physical models calculated using the method of moments. We show that the estimation is significantly improved by modeling the waveform distortion due to the bars. The resulting images are focused and clearly represent the contours of the targets. The algorithm is robust to the ambiguities in bar parameter values. In addition, the minimal necessary SNR is lower compared with the case in which the influence of the bars on the signal shape is ignored.

Sharp-focus image restoration from defocused images

We present a noniterative algorithm for sharp-focus image restoration from multiple defocused images having known relative defocus values between the image planes but unknown absolute defocus values with respect to the in-focus plane. Starting from an arbitrary value of defocus relative to the in-focus plane and using the optical transfer function, the algorithm evaluates the absolute defocus and retrieves the in-focus image of an incoherently illuminated planar object. Experiments with a circular-aperture imaging system confirm the efficiency and robustness of the algorithm. A reconstruction time of approximately 100 ms is attained with two defocused 512x512 pixel images (captured by a 10 bit camera) on a 2.16 GHz laptop.

Quantitative Lorentz transmission electron microscopy of structured thin permalloy films

The defocusing of images of ferromagnetic particles in the transmission electron microscope gives rise to magnetic contrast (Lorentz microscopy). We have developed a theory which allows from this contrast to determine quantitatively the distribution of the magnetic fields of the specimen. The measurements were performed on permalloy particles of disc (diameter 50 nm), and rectangular (25×50 nm2 and 50×50 nm2) shapes, thickness of 21 nm. These particles had a vortex and Landau–Lifshitz structure, respectively. The determined value of the magnetic induction in the material amounted to 1.1±0.1 T. The stray fields in angular sectors of the rectangular particles reached 0.35±0.05 T. The width of the 90° Neel wall between domains turned out to be equal to 4.5±0.5 nm.

A Novel Method For Investigating The Azimuthal Rotation Of Molecular Motors Utilizing Dielectrophoresis And Optical Tweezers

Molecular motors are studied in vitro to understand their Biophysics and Cell Biology. Most mechanical studies of myosin and other molecular motors have utilized surface-immobilized motors or filaments, which impact their range of motion. One way of avoiding surface immobilization of the filament and motor is to suspend filaments from fixed supports, giving the motor or the motor-coated cargo unimpeded freedom of motion about its track (Ali et al., Nat Struct Biol. 9:464, 2002). We used dielectrophoresis at 4-12 V, 2 MHz to stretch and suspend actin filaments across a 2 x 7 um2 trench etched between two gold electrodes patterned on a glass slide. Optical tweezers were used to bring a myosin-coated bead into close proximity to a pre-selected, suspended actin filament, facilitating bead attachment to the filament in motility buffer. Using defocused images, the bead's three-dimensional position was tracked as a function of time to obtain its trajectory on the actin. Experiments were carried out with myosin V and myosin X. Both motor proteins followed left-handed helical paths with 1.5 - 2 um pitch. Variants of this technique will enable types of higher complexity found in cells to be addressed with in vitro experiments. We thank Drs. Mitsuo Ikebe and Osamu Sato for the gift of myosin X and the Nano/Bio Interface Center (NSF NSEC DMR-0425780) and the NIH (grant AR26846) for support.

Effect of the ionosphere on defocusing of space‐based radars

Space‐based synthetic aperture radars can be detrimentally affected by electron density variations in the ionosphere, which cause signal phase variations resulting in image defocusing. In order to evaluate the significance of this problem, this paper determines how often the phase perturbations are large enough to cause defocusing. High cadence GPS TEC signals collected on Ascension Island during sunspot minimum and in Papua New Guinea over half a solar cycle have been analyzed. Both locations lie in the equatorial crest region. For a space‐based synthetic radar operating at 435 MHz, the average probability of defocusing varies from zero at quiet times, to around 1% between 18:00 and 24:00 at solar minimum, and to 45% between 18:00 and 24:00 at solar maximum. Corresponding values are given for radars operating at other frequencies. A method is developed to estimate such variations from the large database of S4 measurements.

Defocusing of echo-delay images for clutter rejection in echolocating bats.

Echolocating big brown bats emit ultrasonic FM sounds containing two prominent harmonics (FM1 and FM2) and perceive target distance from echo delay. Each broadcast and its echoes are processed by time‐domain mechanisms incorporating neuronal delay‐lines for spectrogram correlation. Pulse‐to‐pulse variability requires the bat to store a template of the FM sweeps in each broadcast to recognize its exact echoes. Ordinarily, gradations of mismatch, or decorrelation, between echoes and broadcasts would lead to a correspondingly graded decline in delay accuracy. However, when the relation between FM1 and FM2 is gradually disrupted, bats abruptly lose delay acuity through a process that amounts to deliberate defocusing of the image. Bats actually have two computational pathways for perception of delay—one involving overall delay to determine target range, and the other involving delay differences between glint reflections to determine shape, extracted from the interference spectrum between the overlapping reflections. Defocusing occurs in the shape, or fine delay part of the image, possibly due to failure of the spectrally based transformation process to converge upon a simple solution that would depict a manageably small number of glints from a regular pattern of interference notches. [Work supported by ONR and NIMH.]

Using electrical and optical tweezers to facilitate studies of molecular motors

Dielectrophoresis was used to stretch and suspend actin filaments across a trench etched between two electrodes patterned on a glass slide. Optical tweezers were used to bring a motor protein-coated bead into close proximity to a pre-selected, suspended actin filament, facilitating the attachment of the myosin-coated bead to the filament. The clearance beneath the filament allowed the bead to move freely along and around its filamentous track, unhindered by solid surfaces. Using defocused images, the three-dimensional position of the bead was tracked as a function of time to obtain its trajectory. Experiments were carried out with myosin V and myosin X. Both motor proteins followed left-handed helical paths with the myosin X motor exhibiting a shorter pitch than the myosin V. The combined use of electrostatic and optical tweezers facilitates the preparation of motility assays with suspended tracks. Variants of this technique will enable higher complexity experiments in vitro to better understand the behavior of motors in cells.

Phase front retrieval by means of an iterative shadowgraphic method

In this paper, we propose an iterative shadowgraphic method (ISM) as an interesting alternative to existing methods for self-referencing optical phase retrieval. Two defocused images of the intensity distribution of the light scattered by a weakly absorbing phase object were sufficient to retrieve the transverse phase distribution of the distorted illuminating beam. An algorithm was developed to correct for diffraction effects in phase maps retrieved with a simple shadowgraphic method. We provide a mathematical proof of the convergence of the algorithm to the true profile of the sought phase object. Several numerical tests were performed of the algorithm showing its capability of recovering the full details of the original phase distribution with increased resolution as compared with the simple shadowgraphic method. The convergence of the ISM was also compared numerically with that of a nonoptimized Gerchberg-Saxton-type algorithm and found to be faster and not affected by stagnation problems.

Application of Markov Random Field in Depth Information Estimation of Microscope Defocus Image

Application of Markov Random Field in Depth Information Estimation of Microscope Defocus Image

Improving the Sensitivity of Astronomical Curvature Wavefront Sensor Using Dual-Stroke Curvature

ABSTRACTCurvature wavefront sensors measure wavefront phase aberration by acquiring two intensity images on either side of the pupil plane. Low-order adaptive optics (AO) systems using curvature wavefront sensing (CWFS) have proved to be highly efficient for astronomical applications: they are more sensitive, use fewer detector elements, and achieve, for the same number of actuators, higher Strehl ratios than AO systems using more traditional Shack-Hartmann wavefront sensors. In higher-order systems, however, curvature wavefront sensors lose sensitivity to low spatial frequencies wavefront aberrations. This effect, often described as “noise propagation,” limits the usefulness of curvature wavefront sensing for high-order AO systems and/or large telescopes. In this paper, we first explain how this noise propagation effect occurs and then show that this limitation can be overcome by acquiring four defocused images of the pupil instead of two. This solution can be implemented without significant technology development and can run with a simple linear wavefront reconstruction algorithm at >kHz speed. We have successfully demonstrated in the laboratory that the four conjugation planes can be sequentially obtained at >kHz speed using a speaker–vibrating membrane assembly commonly used in current curvature AO systems. Closed loop simulations show that implementing this scheme is equivalent to making the guide star 1 to 1.5 magnitude brighter for the configuration tested (188 actuator elements on 8-m telescope). Higher sensitivity gains are expected on curvature systems with higher number of actuators.

New focus assessment method for iris recognition systems

In this paper, we propose a new focus assessment method (focus method) for iris recognition systems, which combines the wavelet transform method and the SVM (support vector machine) [Vapnik, V., 1998. Statistical Learning Theory. John Wiley & Sons, NY, USA]. The wavelet-based method estimates focus values by using the ratio of high and low-frequency sub-band averages. The SVM find optimal decision boundary between focused and defocused image with image brightness and focus value as input values. The proposed method has shown distinctive advantages in terms of the following four points. First, by using the proposed wavelet-based method, it detects omni-directional high-frequency which is the characteristic of iris patterns. Second, proposed method can detect slight defocusing of images by using the average of high and low-frequency sub-bands simultaneously. Third, the SVM reduces the error rate of the wavelet-based method by finding the optimum threshold. Fourth, processing time is reduced. It is 213 times faster than the maximum speeds compared with previous spatial domain methods [Kang, B., Park, K., 2006. A study on fast iris restoration based on focus checking. In: LNCS (AMDO 2006), vol. 4069, pp. 19–28; Daugman, J.G., 2004. How iris recognition works. IEEE Trans. Circuits Systems Video Technol. 14, 21–30; Wei, Z., Tan, T., Sun, Z., Cui, J., 2005. Robust and Face Assessment of Iris Image Quality. ICB. pp. 464–471]. For making the reference criteria to compare with the result of focus measures, we propose a schematic model for evaluating the pixel size of SR (specular reflection) in the cornea. To compare with the performance rate, Daugman’s kernel, Kang’s kernel, Wei’s kernel and Kautsky’s method are tested with the proposed method using five different types of data. The proposed method showed the best performance and has shown 3.03% of ER (error rate) using the Yonsei database and 2.62% of ER using the UBIRIS.

Three-dimensional particle imaging by defocusing method with an annular aperture

We propose an annular-aperture-based defocusing technique for three-dimensional (3D) particle metrology from a single camera view. This simple configuration has high optical efficiency and the ability to deal with overlapped defocused images. Initial results show that an uncertainty in depth of 23 microm can be achieved over a range of 10 mm for macroscopic systems. This method can also be applied in microscopy for the measurement of fluorescently doped microparticles, thus providing a promising solution for 3D flow metrology at both macroscales and microscales.

Investigating the correlation between the motions of the images of close stars for laser communications experiments with the artemis satellite

We investigated the correlation between the motions of the images of the components of the double star Gem. The angular distance between the components (4.8) corresponds approximately to the laser communications experiments with the geostationary Artemis satellite. The images were ac- quired with CCD cameras at the ESA's Optical Ground Station (the Canary Islands) and at the AZT-2 telescope of the Main Astronomical Observatory (Kyiv, Ukraine). Short exposures were made every second with narrow filters at a wavelength of about 850 m. Mean photometric positions of the Gem component images and their deviations were determined, and the correlation coefficients for the dis- placements of two images in the X and Y coordinates were calculated: K X = 0.96 and K Y = 0.95. The defocusing of the images was examined with the use of their full widths at half-maximum. We demon- strate that the atmospheric turbulence in the laser communications experiments with the geostationary satellite Artemis can be compensated for with the use of the data on the image motion observed in the di- rection toward the visible position of the satellite.

Calibration of defocus blur for zoom lenses

Depth from defocus(DFD) measures defocus blur, which determines the point spread function (PSF) of an image formation system. Most DFD research has been investigated with a fixed focal length, where two or more defocus images are obtained with different image distances or lens apertures. To apply DFD techniques using a zoom lens, extensive calibration of the image formation system is needed. This work presents a simple calibration technique of defocus blur for a zoom lens system. We derive the relationship of defocus blur with respect to different focal lengths of the lens. The proposed technique is applied to a spatial domain DFD technique for error analysis.