Showing papers on "Moiré pattern published in 2019"

High precision computer-generated moiré profilometry

Abstract: Recently, a computer-generated moire profilometry was proposed by our research group. It can effectively avoid the influence of the transient caused by moire fringes’ direct acquisition and generally owns a higher accuracy. But when the spatial spectrum of the captured deformed pattern is severely aliased caused by the measured object, the accuracy of this method may be affected to some extent due to the impure background light component extraction. So, a high precision computer-generated moire profilometry based on background light component’s accurate elimination is proposed. By adding an additional special phase-shifting sinusoidal grating to accurately extract valid information in the spatial domain and improve the sinusoidal feature of the pattern, the measurement precision can be improved effectively. Though the single-shot feature is broken, the real-time measuring feature is still maintained successfully. Experimental results show the feasibility and validity of the proposed method.

Rotation-Selective Moiré Magnification of Structural Color Pattern Arrays.

Abstract: When a microlens array is aligned and overlaid on an array of patterns with similar periodicity, a highly magnified image of the patterns is observed. This effect, known as moire magnification, is ...

Design of a light-field near-eye display using random pinholes.

Abstract: Light-field near-eye displays can solve the accommodation/convergence conflict problem that can cause severe discomfort to the user. However, in actual systems, convergence depth and accommodation depth may not match each other due to the repeated zones or flipped images produced by traditional light-field methods. Also, Moire fringes are another problem which is caused by interaction between two periodic structures. We present a method of constructing a light-field near-eye display based on random pinholes, where the random structure is employed as a spatial light modulator to break the periodicity of elemental images. Light-field images for a unique view zone in space without Moire fringes can be provided. A proof-of-concept prototype has been developed to verify the proposed method.

Color moiré reduction and resolution enhancement of flat-panel integral three-dimensional display

Abstract: Color moire occurs owing to the subpixel structure of the display panel in the integral three-dimensional (3D) display method, deteriorating the 3D-image quality. To address this, we propose a method for reducing the color moire and improving the 3D-image resolution, simultaneously, by combining multiple 3D images. In the prototype system, triple 3D display units with lens arrays closely attached to 8K-resolution display panels are optically combined. By controlling the color moire of the 3D image generated on each display and shifting and combining the elemental lenses constituting the lens array, sufficient reduction in the color moire is realized, while suppressing the deterioration of the 3D-image quality, at a distant position from the lens array in the depth direction, along with an approximately two-fold enhancement of the resolution near the lens array.

Ultra-large moiré-less autostereoscopic three-dimensional light-emitting-diode displays.

Abstract: Large-scale autostereoscopic three-dimensional (3D) light-emitting-diode (LED) displays can provide high-quality, even immersive, visual experiences. However, the unique structural characteristics of the LED display panel can enhance moire effects during parallax generation. We present a novel method for quantitatively characterizing the moire effect in autostereoscopic 3D-LED displays using a model applying geometrical ray tracing and a brightness distribution stack. An optical diffuser (OD) device for moire reduction and performance balance is designed and the influence of several key device parameters on moire pattern features are examined in autostereoscopic 3D-LED displays for the first time. Using the obtained optimal parameters, we assembled an ultra-large moire-less autostereoscopic 3D-LED display prototype, which was experimentally shown to be capable of reducing moire fringes without noticeable increase in crosstalk or significant reduction in visual quality. Finally, the effects on the moire and crosstalk effect of altering key influencing factors were examined.

Automatic image-domain Moiré artifact reduction method in grating-based x-ray interferometry imaging.

Abstract: In this study, we propose to remove Moire image artifact induced by system instabilities in grating-based x-ray interferometry imaging using convolutional neural network (CNN) technique. This method reduces Moire image artifact in image-domain via a learned image post-processing procedure, rather than developing signal retrieval optimization algorithms to minimize the inconsistencies between acquired phase stepping data and assumed signal model. To achieve this aim, we suggested to train the CNN network using dataset synthesized from both natural images and experimentally acquired Moire artifact-only images. In particular, a novel approach is developed to generate a large number of various high quality Moire artifact-only images from finite groups of experimental phase stepping data. Both numerical and experimental results demonstrate that the developed CNN method is able to effectively remove the undesired Moire image artifact. As a result, the image quality of a practical grating-based x-ray interferometry system can be greatly improved.

High-Resolution Angular Displacement Technology Based on Varying Moiré Figure Phase Positions

Abstract: Angular displacement measurement is a popular research subject. The grating of traditional angular measurement devices uses multi-circle code and is difficult to miniaturize. This paper proposes a novel angular displacement technology based on varying moire figure phase positions which allows for reduced volume and high-resolution angle measurements in small-size gratings. First, a moire figure phase model is established and the calculation arithmetic is written. Second, the proposed arithmetic based on differences in moire figure phase positions is completed accordingly. At last, a test device was fabricated based on the proposed theory with a total diameter of 35 mm and grating diameter of 25 mm. These tests show that angular displacement method based on differences of moire figure phase positions can achieve a high resolution measurement when the diameter of calibration grating is small. We hope the results of this paper provide a workable theoretical foundation for future photographic encoders.

Automatic image-domain Moire artifact reduction method in grating-based x-ray interferometry imaging

Abstract: The aim of this study is to demonstrate the feasibility of removing the image Moire artifacts caused by system inaccuracies in grating-based x-ray interferometry imaging system via convolutional neural network (CNN) technique. Instead of minimizing these inconsistencies between the acquired phase stepping data via certain optimized signal retrieval algorithms, our newly proposed CNN-based method reduces the Moire artifacts in the image-domain via a learned image post-processing procedure. To ease the training data preparations, we propose to synthesize them with numerical natural images and experimentally obtained Moire artifact-only-images. Moreover, a fast signal processing method has also been developed to generate the needed large number of high quality Moire artifact-only images from finite number of acquired experimental phase stepping data. Experimental results show that the CNN method is able to remove Moire artifacts effectively, while maintaining the signal accuracy and image resolution.

Multi-Wavelength Digital-Phase-Shifting Moiré Based on Moiré Wavelength

Abstract: Multi-wavelength digital-phase-shifting moire was demonstrated using multiple moire wavelengths determined by system calibration over the full working depth. The method uses the extended noisy phase map as a reference to unwrap the phase map with a shorter wavelength, and thus achieve a less noisy and more accurate continuous phase map. The moire wavelength calibration determines a moire-wavelength to height relationship that permits pixelwise refinement of the moire wavelength and height during 3D reconstruction. Only a single pattern has to be projected and, thus, a single image captured to compute each phase map with a different wavelength to perform digital-phase-shifting moire temporal phase unwrapping. Only two captured images are required for two-wavelength phase unwrapping and three captured images for three-wavelength phase unwrapping. The method has been demonstrated in the 3D surface-shape measurement of an object with surface discontinuities and spatially isolated objects.

Strain measurement of a channel between Si/Ge stressors in a tri-gate field effect transistor utilizing moire fringes in scanning transmission microscope images

Abstract: We measure the strain of a channel between Si/Ge stressors in a tri-gate p-channel metal–oxide semiconductor device, known as a fin field-effect transistor (FinFET), by utilizing moire fringes in scanning transmission electron microscopy (STEM). These fringes reveal a pseudomagnified Si lattice, resulting from undersampling of the crystalline lattice with the nodes of the scanning grid of STEM. A practical device sample is prepared using a focused ion-beam instrument. The sample lamella is cut along the X direction to allow observation of the strained channel between Si/Ge stressors. The measurement of channel strain in a FinFET is not easy, since the channel is sandwiched between top and bottom layers of gate electrodes and insulators. For the strain measurement, we use the moire fringes of the Si[220] lattice. These moire fringes extract only the targeted lattice and act as a real spatial frequency filter. Other fringes with different directions and/or spacings are thereby filtered out. The strain along the channel between the Si/Ge stressors is measured to be −0.9%, with the whole procedure taking less than 5 min, including data acquisition time, using a dedicated program. As the fringe contrast is weak owing to disturbances by the gate and insulator layers, a microscope is equipped with an aberration corrector in the probe-forming system to enhance the contrast. The proposed method offers a high-throughput strain measurement, since it is performed in the image acquisition mode, and is easily incorporated into the standard workflow for critical dimension measurements.We measure the strain of a channel between Si/Ge stressors in a tri-gate p-channel metal–oxide semiconductor device, known as a fin field-effect transistor (FinFET), by utilizing moire fringes in scanning transmission electron microscopy (STEM). These fringes reveal a pseudomagnified Si lattice, resulting from undersampling of the crystalline lattice with the nodes of the scanning grid of STEM. A practical device sample is prepared using a focused ion-beam instrument. The sample lamella is cut along the X direction to allow observation of the strained channel between Si/Ge stressors. The measurement of channel strain in a FinFET is not easy, since the channel is sandwiched between top and bottom layers of gate electrodes and insulators. For the strain measurement, we use the moire fringes of the Si[220] lattice. These moire fringes extract only the targeted lattice and act as a real spatial frequency filter. Other fringes with different directions and/or spacings are thereby filtered out. The strain along...

Minimization of Moiré effect generated by a double-layered metal mesh on top of the R-G-B optical source

Abstract: Fourier transform was utilized to analyze Moire pattern for a two-layer metal mesh structure nonadjacent to an intensity patterned light source with a micron size separation. In order to obtain the full understanding of human sensitivity, we applied the contrast sensitivity function as well as Snell’s law considering oblique observation direction. We applied a general case of a two-layer sensor structure model as the periodic metallic array, where the metal meshes were distributed in two different layers with a microscopic gap. Applying different values of in-plane mesh angles and periodicities of the metal mesh which is located above the intensity patterned light sources, we investigated the mechanism of Moire generation. According to multiplicative model the influences of 70 in-plane mesh angles, 60 mesh periodicities, various observer angles and distances with respect to the display panel on the standard deviation of Moire were thoroughly investigated to calculate the optimal parameters which provided less visibility of Moire. The simulation results were in good agreement to a prior analytical method. Moreover, the experimental results confirmed the suggested critical parameters with less Moire conditions calculated based on our numerical model. Our proposed approach is rigorously applicable for various size of display systems with more complex metal meshes.

Three-dimensional shape, displacement, and strain measurement device and method using periodic pattern, and program therefor

Abstract: In a conventional moire method, achieving both measurement accuracy and dynamic measurement and balancing field of view and measurement accuracy have been difficult. The present invention makes it possible to handle conventional moire fringes as a grating for generating phase-shifted second-order moire fringes, use a spatial phase shift method algorithm to accurately analyze the phases of the second-order moire fringes before and after deformation, and determine shape from the phase differences between gratings projected onto the surface of an object of measurement and a reference surface and determine deformation and strain from the phase differences between the second-order moire fringes, before and after deformation, of a repeating pattern on the object surface or a produced grating. As a result, it is possible to measure the three-dimensional shape and deformation distribution of an object accurately and with a wide field of view or dynamically and with a high degree of accuracy.

Improvement of fringe quality for phase extraction in double digital fringe projection

Abstract: A procedure to improve the quality of the extracted phase by a passband filter within the spatial frequency domain is proposed, using the double-digital fringe projection method for obtaining the contour of the surface of different objects. This method requires the digital projection of two fringe patterns to the same object to generate an interference pattern containing moire fringes, which are related to the shape of the measured object. The proposed method pretends to remove remnant frequencies of the projected fringes keeping only the moire pattern.

Optical distortion evaluation based on the Integrated Colour CCD Moiré Method.

Abstract: Camera calibration is an important part of high-precision optical measurement, which is especially difficult in the micro-nano field. Based on the integrated correlation calculation and CCD moire method, this paper describes the development of a lens calibration technique called the Integrated Colour CCD Moire Method (ICCM). The CCD moire fringes, formed by superimposing a periodic optical signal of a specimen grating with a CCD target array or a Bayer filter array, significantly enlarges the deformation modulated by lens distortion and the calibration plate attitude (i.e. the rotation angle relative to the camera coordinate system). To measure lens distortion using CCD moire, the deformation pattern that is governed by the lens distortion, specimen grating attitude and carrier was used to construct a CCD fringe image. If the constructed CCD fringe image based on the trial lens distortion and rotation angles have a maximum similarity to the captured CCD moire image, the lens distortion and rotation angles are correctly inversed. Particle swarm optimisation algorithm was selected to search for the true value so that the accuracy and robustness could be improved. Numerical experiments verified that the ICCM method developed in this work can simultaneously inverse the lens distortion, rotation angle and the grating pitch with high precision. The lens distortion of the metallographic microscope has been successfully characterised by the developed method with an 833 nm pitch grating. Simulations and experiments showed that ICCM is an intuitive, accurate, anti-noise and robust distortion calibration method.

Displacement measurement using Talbot effect

Abstract: Linear gratings and circular gratings are most commonly used in the applications of Talbot effect, due to their simple patterns and ease of analysis of Moire fringes. In the present paper, we demonstrate a scheme to measure the displacement of a deformed object which based on the Talbot effect. We designed a hologram of a two-dimensional square-hole grating. For the test, we used a computer-controlled liquid crystal spatial light modulator (LC–SLM) and the computer-generated Talbot array hologram. The Talbot array hologram is displayed on the LC–SLM screen. The beam diffracted by the grating is transmitted to the surface of an object. By adjusting the distance between the LC-SLM and the object, a clear image is formed on the surface of the object. A speckled pattern of the object surface is captured by a CCD camera. Two speckle patterns before and after the deformation is recorded. The information about the displacement is codified in the intensity pattern. The displacement can be obtained by digital image correlation (DIC). The DIC obtains the displacement components by comparing the gray intensity changes between the digital images of an object surface before and after the deformation. This method is simple and easy, and can be used as an alternative method to measure in-plane and out-of-plane displacements. Theoretical and experimental results are presented.

Color Moiré Reduction Method for Thin Integral 3D Displays

Abstract: The integral three-dimensional (3D) display is an ideal visual 3D user interface. It is a display method that fulfills many of the physiological factors of human vision. However, in integral 3D displays for mobile applications that use a direct viewing flat panel to display elemental images, the occurrence of color moire is a problem owing to the sampling of subpixels by the elemental lenses and the insufficient resolution and depth reproduction performance of the reconstructed 3D image. We propose a method to solve these problems that utilizes optical wobbling spatiotemporal multiplexing using a birefringent element and a polarization controller. With the conventional moire reduction method, the degree of defocus of el-ementallenses has to be set to a large value, which has also been a factor that reduces the depth reproduction performance. We show that effective color moire reduction can be achieved with a slight defocus of elemental lenses and without deteriorating depth reproducibility by using the proposed optical wobbling method.

Digital Moire interference phase real-time measurement method based on sparse Fourier transform

Abstract: The invention relates to a digital Moire phase shift interference phase real-time measurement technology based on sparse Fourier transform, and belongs to the optical measurement field. Firstly, a virtual interference pattern is constructed, and Moire synthesis is performed. On the basis of one-dimensional sparse Fourier transform (SFFT), a two-dimensional Moire fringe pattern rearrangement rule is designed, and a small number of frequency spectrum amplitude large-value points in a frequency spectrum are sparsely dispersed in the frequency spectrum through spatial domain rearrangement. Secondly, a two-dimensional SFFT window function is set, spatial domain aliasing and down-sampling FFT of two-dimensional signals are performed, an original image with a size of N*N is reduced to the size ofB*B, and a subsequent calculation amount is reduced. And frequency spectrum reduction with the N*N size is completed through position coordinate reduction and estimated value reduction. And finally,a restored frequency spectrum is applied to a phase solution process of a digital Moire phase shift method. In the invention, a calculation amount of the phase solution process can be reduced, an algorithm speed of the digital Moire phase shift phase solution method is improved, and real-time measurement of a phase in fields of precision processing, engineering practice and biomedicine can be realized.

A Phase Compensation Method for Phase Extraction of Abrupt Surfaces in Projection Moiré

Abstract: Projection moire method is a high-resolution, non-contacting and full-field optical measurement technique. But the 2π-ambiguity problem in phase unwrapping limits the phase difference between neighbouring pixels under π which makes projection moire method ineffective at measuring abrupt surfaces or steps. This paper aims at putting forward a phase compensation method to solve this 2π-ambiguity problem in projection moire. Since the phase of moire pattern is the variance between the phase of specimen grating on object’s surface and the phase of the reference grating, our method is to calculate the phases of specimen grating and the reference grating respectively, regard their difference as the phase of the moire pattern in theory and correct the wrong unwrapped moire fringe phase with integral multiple of 2π. In order to acquire the phase of specimen grating which also has the 2π-ambiguity problem, using multiple fringe pictures with different pitches. The experiments successfully reconstruct two objects with discontinuities in their surfaces. This phase compensation technique no longer requires us to count fringe orders or find a reference point to mark the zero-order moire fringe during experiments.

Quantitative differential phase microscopy based on structured illumination

Abstract: Structured illumination microscopy (SIM) is a well-known super-resolution imaging technique, which exploits moire patterns created when a sample is illuminated with periodic stripes. Conventional SIM often applies to fluorescent samples, or the samples which have absorption on illumination light. Here we report quantitative phase imaging of transparent samples with a SIM apparatus in transmittance-mode. For this purpose, two sets of fringe patterns, which have two orthogonal orientations and five phase-shifts for each orientation, were generated by a digital micro-mirror device (DMD) and projected on a sample. Under different fringe illuminations slightly-defocused images of the sample were recorded sequentially by a CCD camera, where the object waves along the ±1st orders of the illumination interfere with each other with a lateral shear in-between. The phase derivatives of the sample along the shear direction can be reconstructed from the phase-shifted intensity patterns. Eventually, the quantitative phase distribution of the sample was obtained by integrating the two phase derivatives. Furthermore, an iterative algorithm was used to enhance the resolution of the phase image, considering the structured illumination synthesizes a larger spectrum in the Fourier domain, similar to oblique illuminations in digital holography. This apparatus can also work in the conventional SIM mode, which images fluorescent samples in an in-focus manner. We believe such simple and versatile apparatus will be widely applied to biological imaging or industrial inspection.

Theoretical study of the properties of X-ray diffraction moiré fringes. II. Illustration of angularly integrated moiré images.

Abstract: Using a theory of X-ray diffraction moire fringes developed in a previous paper, labelled Part I [Yoshimura (2015). Acta Cryst. A71, 368–381], the X-ray moire images of a silicon bicrystal having a weak curvature strain and an interspacing gap, assumed to be integrated for an incident-wave angular width, are simulation-computed over a wide range of crystal thicknesses and incident-wave angular width, likely under practical experimental conditions. Along with the simulated moire images, the graphs of characteristic quantities on the moire images are presented for a full understanding of them. The treated moire images are all of rotation moire. Mo Kα1 radiation and the 220 reflection were assumed in the simulation. The results of this simulation show that fringe patterns, which are significantly modified from simple straight fringes of rotation moire, appear in some ranges of crystal thicknesses and incident-wave angular width, due to a combined effect of Pendellosung oscillation and an added phase difference from the interspacing gap, under the presence of a curvature strain. The moire fringes which slope to the perpendicular direction to the diffraction vector in spite of the assumed condition of rotation moire, and fringe patterns where low-contrast bands are produced with a sharp bend of fringes arising along the bands are examples of the modified fringe pattern. This simulation study provides a wide theoretical survey of the type of bicrystal moire image produced under a particular condition.

Passive range finder based on moiré images of Ronchi-like gratings with bilateral asymmetry.

Abstract: A passive range-finding technique utilizing moire images of Ronchi-like gratings with bilateral asymmetry, specifically fork gratings, is explored. Fork gratings are used as opposed to Ronchi gratings due to their asymmetry in the spatial and frequency domains, which enable the resolution of certain ambiguities in analysis that would otherwise be present. The two patterns which are convolved to produce the moire image are the fork grating and the nailbed pattern of the pixelated detector. A fork grating of known size and spatial frequency is imaged with a detector of a fixed pixel pitch. Multiple analysis techniques are applied in frequency space, which lead to both relative and absolute measures of distance.

A directional flat-panel antenna

Abstract: A compact, flat beam steerable antenna is described. The antenna includes a waveguide for conveying electromagnetic energy and an adjustable moire pattern assembly disposed adjacent to the waveguide. The moire pattern assembly is arranged to present varying moire patterns comprised of regions of contrasting conductivity. In use, a direction for transmission of the electromagnetic radiation through the moire pattern assembly can be varied by operation of the assembly to alter the moire pattern.

Liquid refractive index measurement method based on equal-thickness interference moire fringes

Abstract: The invention discloses a liquid refractive index measurement method based on equal-thickness interference moire fringes. The adopted device comprises a monochromatic light source and an air wedge with a wedge angle formed by two pieces of glass, wherein the bottom face of the air wedge is horizontally placed on a workbench, and gradual-change spacing stripes are preset on the upper surface of theair wedge and marked with corresponding refractive index values; a liquid to be measured is injected into the air wedge, the monochromatic light source is vertically incident on the air wedge to generate equal-thickness interference fringes, the equal-thickness interference fringes and the gradual-change spacing fringes are overlapped to generate moire fringes, and the refractive index of the liquid to be measured is determined according to the position of the unique linear moire fringes. The problems that in the prior art, the measurement process is complex, the calculation process is needed, or although direct reading can be achieved, the measurement range is limited by materials of a measurement instrument are solved.

Method for visualization of macrodefects of dynamic periodic structures, based on the effect of the emergence of moire fringes

Abstract: 1 ORCID: 0000-0002-1525-0526, avlasevichnt@tut.by 2 ORCID: 0000-0002-5761-4965, anufrick@grsu.by 3 ORCID: 0000-0003-2525-6611, amlialikov@grsu.by Abstract Of particular interest are objects characterized by a tunable periodic structure. The structure parameters of such objects change not only in space, but also in time. The study of behavior in space and visualization of defects in periodic structures is one of the main tasks of measuring control. The paper proposes a simple method of visualization of macrodefects of dynamic periodic structures based on the effect of the appearance of moire fringes. An easy-to-use visualization method involves registering a series of snapshots of a dynamic periodic structure followed by combining a selected pair of snapshots. The devices for recording a series of snapsohts and forming moiré paintings are described. A feature of the implementation of this method of visualization of macrodefects is the possibility of using incoherent light both when registering snapsohts and in the process of forming moire fringes. When creating a device for implementing the method, household LED lamps A60 with a matte bulb were used as light sources. A series of moire patterns was obtained, visualizing the spatial position of the macrodefect of the mask surface at various points in time of its mechanical deformation. A pattern of moire fringes, visualizing the position of a macrodefect of a periodic structure, was recorded by a digital camera and displayed on a personal computer monitor screen.

Scanning method for weakening moire in scanning electronic beam imaging

Abstract: The invention discloses a scanning method for weakening moire in scanning electronic beam imaging. The scanning method is used for scanning a periodic image, and comprises the following steps: S01, determining a scanning direction as a periodic direction of an image, and defining the scanning direction as a line direction of the image; dividing the image into M lines and N rows; S02, dividing eachline of image into X regions, wherein X is integer greater than zero; S03, scanning each region in the first line by an electronic beam according to a disorder scanning path, wherein the disorder scanning paths in X regions are same; and S04, repeating step S03 until the M line scanning of the periodic image. Through the scanning method for weakening moire in scanning electronic beam imaging, theordered scanning paths in the scanning electron microscope are changed as the disorder scanning paths, so that the moire strength can be weakened or the moire is eliminated when the scanning electronmicroscope scans the periodic images.

Crystal analyzer and method for analyzing crystals

Abstract: To provide a crystal analyzer that can accurately detect a crystal strain or a crystal defect in a crystal.SOLUTION: The crystal analyzer according to an embodiment includes: a first storage unit for storing a first image including a crystal lattice image in a crystal region of a sample including a crystal region; a first image processing unit for generating a moire image from the crystal lattice image; a second storage unit for storing at least one of the correspondence relation between the pattern of the moire stripe of a moire image and the crystal defect and the correspondence relation between the pattern of the moire stripe of the moire image and the crystal strain; and an analysis unit for analyzing the moire image generated from the crystal lattice image with reference to at least one of the correspondence relations and detecting at least one of the crystal defect and the crystal strain in the crystal region.SELECTED DRAWING: Figure 1