Showing papers on "Moiré pattern published in 2020"

Strain measurement in semiconductor FinFET devices using a novel moiré demodulation technique

Abstract: Moire fringes are used throughout a wide variety of applications in physics and engineering to bring out small variations in an underlying lattice by comparing with another reference lattice. This method was recently demonstrated in Scanning Transmission Electron Microscopy imaging to provide local strain measurement in crystals by comparing the crystal lattice with the scanning raster that then serves as the reference. The images obtained in this way contain a beating fringe pattern with a local period that represents the deviation of the lattice from the reference. In order to obtain the actual strain value, a region containing a full period of the fringe is required, which results in a compromise between strain sensitivity and spatial resolution. In this paper we propose an advanced setup making use of an optimised scanning pattern and a novel phase stepping demodulation scheme. We demonstrate the novel method on a series of 16 nm Si-Ge semiconductor FinFET devices in which strain plays a crucial role in modulating the charge carrier mobility. The obtained results are compared with both Nano-beam diffraction and the recently proposed Bessel beam diffraction techniques. The setup provides a much improved spatial resolution over conventional moire imaging in STEM while at the same time being fast and requires no specialised diffraction camera as opposed to the diffraction techniques we compare to.

Switchable Asymmetric Moiré Patterns with Strongly Localized States.

Abstract: Most moire pattern structures are constructed by twisting the angle of two similar 2D materials. The corresponding electronic structures are fixed in device applications. Here we study moire patter...

Single-shot digital phase-shifting Moiré patterns for 3D topography.

Abstract: A simple and robust technique of Moire topography with single-image capture and incorporating digital filtering along with a four-step digitally implemented phase-shifting method is introduced for three-dimensional (3D) surface mapping. Feature details in the order of tens to hundreds of microns can be achieved using interferometrically generated structured light to illuminate the object surface. Compared to the traditional optical phase-shifting method, a digital phase-shifting method based on Fourier processing is implemented with computer-generated sinusoidal patterns derived from the recorded deformed fringes. This enables a single capture of the image that can be used to reconstruct the 3D topography of the surface. Single-shot imaging is simple to implement experimentally and avoids errors in introducing the correct phase shifts. The feasibility of this technique is verified experimentally, and applications to metallic surfaces are demonstrated.

Second-order moiré method for accurate deformation measurement with a large field of view.

Abstract: In this study, we propose a second-order moire method by performing digital sampling at two stages to realize high-accuracy deformation measurement in a wide field of view, where a grid image is recorded at a low magnification. Simulations have verified that this method has high strain measurement accuracy when the grid pitch is close to or even smaller than two pixels for both parallel and oblique grids with random noise. As an application, the two-dimensional microscale strain distributions of a carbon fiber reinforced plastic specimen when the grid pitch was about 2.1 pixels were presented. Shear strain concentration was detected before an interlaminar crack emerged, and tensile strain concentration was found prior to the occurrence of a transverse crack. The proposed method makes the two-step phase-shifting technique achieved indirectly, not only enlarging the field of view, but also maintaining the measurement accuracy.

Modified color CCD moiré method and its application in optical distortion correction

Abstract: The characterization and correction of lens distortion is an important part of optical measurement. This work analyzes the formation mechanism of color fringes and multiplication moire, and discusses modification of the color CCD moire method for correcting lens distortion. A demosaicing algorithm was used to simulate the color fringes in a CCD moire pattern. We then performed a detailed analysis of the carrier field, and adopted a universal polynomial distortion model to characterize lens distortion, which increased the accuracy of distortion correction. Comparison experiments verified the feasibility of the modified method and the correctness of the formation mechanism for color CCD moire. The modified method was then applied to lens distortion correction in the DIC measurement process, effectively reducing errors in displacement measurement.

Sampling moiré method: a tool for sensing quadratic phase distortion and its correction for accurate quantitative phase microscopy

Abstract: The advantages of quantitative phase microscopy (QPM) such as label-free imaging with high spatial sensitivity, live cell compatibility and high-speed imaging makes it viable for various biological applications. The measurement accuracy of QPM strongly relies on the shape of the recorded interferograms, whether straight or curved fringes are recorded during the data acquisition. Moreover, for a single shot phase recovery high fringe density is required. The wavefront curvature for the high-density fringes over the entire field of view is difficult to be discerned with the naked eye. As a consequence, there is a quadratic phase aberration in the recovered phase images due to curvature mismatch. In the present work, we have implemented sampling moire method for real-time sensing of the wavefront curvature mismatch between the object and the reference wavefronts and further for its correction. By zooming out the interferogram, moire fringes are generated which helps to easily identify the curvature of the fringes. The wavefront curvature mismatch correction accuracy of the method is tested with the help of low temporal coherent light source such as a white light (temporal coherence ∼ 1.6 µm). The proposed scheme is successfully demonstrated to remove the quadratic phase aberration caused due to wavefront mismatch from an USAF resolution target and the biological tissue samples. The phase recovery accuracy of the current scheme is further compared with and found to better than the standard method called principle component analysis. The proposed method enables recording of the corrected wavefront interferogram without needing any additional optical components or modification and also does not need any post-processing correction algorithms. The proposed method of curvature compensation paves the path for a high-throughput and accurate quantitative phase imaging.

Combination of Convolutional and Generative Adversarial Networks for Defect Image Demoiréing of Thin-Film Transistor Liquid-Crystal Display Image

Abstract: In thin-film transistor liquid crystal display (TFT-LCD) manufacturing, the automatic recognition and classification of defects can help manufacturers monitor abnormalities, identify potential process problems, and swiftly respond to these process problems Thus, yield loss can be reduced However, capturing the content displayed on screen using cameras is challenging because it is often contaminated with moire patterns Moire patterns originate from the interference between the pixel grids of inspection camera sensors and panel screens and adversely affect the visual quality of images, causing difficulty in determining the defect type, especially mura defects Therefore, eliminating moire patterns in defect images without impairing image quality is critical However, moire patterns are often dynamic and vary with sensor resolution, distance, and direction Moreover, the frequency distribution of moire patterns is broad, encompassing both low- and high-frequency components Therefore, demoireing is more challenging than other image restoration tasks We investigated this problem and proposed an approach to eliminate moire patterns from defect images based on a generative adversarial network architecture by using the U-net network as a generator and adding a discriminator Moreover, we added an attention mechanism to focus on the local consistency of the restored moire regions The peak-signal-to-noise ratio (PSNR) and structural similarity index measure (SSIM) obtained using the proposed model were compared with those obtained using the U-net and pixel-to-pixel models The experimental results of this study demonstrated that the proposed method can efficiently remove moire patterns from defect images, and the proposed method quantitatively and qualitatively outperforms other methods

Moire Image Restoration using Multi Level Hyper Vision Net

Abstract: A moire pattern in the images is resulting from high frequency patterns captured by the image sensor (colour filter array) that appear after demosaicing. These Moire patterns would appear in natural images of scenes with high frequency content. The Moire pattern can also vary intensely due to a minimal change in the camera direction/positioning. Thus the Moire pattern depreciates the quality of photographs. An important issue in demoireing pattern is that the Moireing patterns have dynamic structure with varying colors and forms. These challenges makes the demoireing more difficult than many other image restoration tasks. Inspired by these challenges in demoireing, a multilevel hyper vision net is proposed to remove the Moire pattern to improve the quality of the images. As a key aspect, in this network we involved residual channel attention block that can be used to extract and adaptively fuse hierarchical features from all the layers efficiently. The proposed algorithms has been tested with the NTIRE 2020 challenge dataset and thus achieved 36.85 and 0.98 Peak to Signal Noise Ratio (PSNR) and Structural Similarity (SSIM) Index respectively.

Static moiré patterns in moving grids.

Abstract: We describe an optical phenomenon of unmovable moire patterns in sliding (moving) grids and gratings. The phenomenon was observed visually in the planar straight movement of the black-and-white gratings with a period of several mm. This is a velocity-independent effect confirmed analytically and in a computer simulation based on the spatial averaging. We found the static directions of the moire patterns in the regular grids, but our technique can be also applied to other objects. The orientation and period of the static moire patterns are not obvious, especially in the presence of the distance effect. The phenomenon can be practically used in security applications.

Modeling the Moiré fringe visibility of Talbot-Lau X-ray grating interferometry for single-frame multi-contrast imaging

Abstract: Moire fringe method in X-ray grating interferometry is characterized by its advantage to obtain multi-contrast data through single-frame imaging However, how the visibility of the Moire fringe is influenced by the system parameters, such as the misalignment angle, still lacks investigation, although it closely relates to the signal-to-noise ratio of the image data In this paper, a simplified model of the Moire fringe visibility is presented, which reveals that the Moire fringe visibility can be expressed as the product of a misalignment-angle-related "sinc" function and a relatively independent factor The following experimental results further suggest that the crosstalk between the detector pixels in the direction perpendicular to the Moire fringe orientation is another main cause for the visibility reduction of the Moire fringes

Single-shot Digital Phase-shifting Moiré Pattern for 3D Metallic Surface Imaging

Abstract: A four-step digital phase-shifting method using Moire patterns and single shot recording is proposed and conducted to map submillimeter-scale 3D surface features.

3-DOF measurement method for non-diffracting Moiré fringes based on CGH

Abstract: Aiming at the motion errors of the linear stage, a measurement method for the determination of three-degree-of-freedom (3-DOF) error motions is proposed based on non-diffracting Moire fringes produced by computer-generated holograms (CGHs). A liquid crystal spatial light modulator (SLM) is used to generate non-diffracting beams, and two non-diffracting beams form Moire fringes. A 3-DOF measuring optical path of non-diffracting Moire fringes is designed. Meanwhile, a 3-DOF mathematical model of motion errors is established, and three kinds of motion errors (yaw angle, roll angle and pitch angle) are separated by geometric analysis method. A rotary table is used to simulate the 3-DOF motion errors on different conditions. The NDB and non-diffracting Moire fringe patterns are obtained by CCD1 and CCD2 respectively. Experimental results show that the motion errors calculated by the positions of the central points agree well with the theoretical value with the error less than 0.0104°, which can verify the feasibility and correctness of the 3-DOF measurement system for non-diffracting Moire fringes.

Real-time computer-generated moiré profilometry with adaptive filtering algorithm

Abstract: A real-time computer-generated moire profilometry (CGMP) with adaptive filtering algorithm is proposed. In CGMP proposed previously, only one static sinusoidal grating needs to be projected onto the measured object and only one deformed pattern caused by the object needs to be captured, which is ideal for real-time three-dimensional (3-D) measurement. By means of generating moire fringes between the captured deformed pattern and the prestored fringe patterns on the reference plane via computer, the 3-D shape of the measured object can be reconstructed successfully. In phase calculating, this method needs to extract the DC component by filtering. If filtering operation required manual intervention each time, its real-time measuring feature may be limited. For this, an adaptive filtering algorithm based on the maximum fundamental frequency component proportion evaluation function is proposed. It can automatically retrieve an object’s phase information according to the Fourier spectrum distributions of different measured objects without any manual intervention. Experimental results demonstrate the feasibility and validity of the real-time 3-D measuring application.

New Design for Compact Color Screen Sets for High-End Digital Color Press

Abstract: Digital halftoning is an essential part of the process for printing color, continuous-tone content. Traditionally, the highest quality has been achieved with analog, offset lithographic presses, using color screen sets that yield periodic, clustered-dot halftone patterns. Increasingly, these systems are being supplanted by digital presses that are based on either electrophotographic or inkjet marking processes. Due to the inherent instability of the electrophotographic marking process, periodic, clustered-dot halftone patterns are also widely used with such presses. However, digital presses have much lower resolution than their analog counterparts. Simply mimicking the traditional screen designs used with commercial, offset presses will result in halftone patterns that are more susceptible to moire due to the interaction between the periodic patterns used to render the different color channels. This causes instability in the printed colors. The moire can be reduced by increasing the frequency of the halftone patterns. But this may make the print appear grainier than its analog counterpart. In this paper, we introduce a principled design procedure that allows one to design color screen sets that generate periodic, clustered-dot halftone patterns that improve color stability without increasing graininess. We present experimental results to support the benefits of our new color screen set design framework.

Random phase-shifting digital holography based on a self-calibrated system.

Abstract: Random phase-shifting digital holography based on a self-calibrated system is proposed. In the proposed method, the hologram and the calibration interference fringes can be recorded simultaneously in a single image based on the space-division-multiplexing technique. Three randomly phase-shifted holograms and corresponding interference fringes are recorded, and the phase-shifting amount between each two adjacent holograms is calculated by the sampling Moire method from the calibration interference fringes. A reflective object is used to demonstrate the effectiveness of the proposed method in the numerical and experiment.

Computer-generated moiré profilometry based on fringe-superposition

Abstract: A computer-generated moire profilometry based on algebraic addition instead of algebraic multiplication is proposed. Firstly, the two AC components of the captured fringe patterns on the reference plane with [Formula: see text] phase difference are retrieved and saved in advance. While measuring, two sinusoidal gratings with [Formula: see text] phase difference are projected onto the measured object alternatively, and the corresponding deformed patterns are captured. Then the AC component of the captured deformed pattern can be separated exactly. When the positive and negative AC component of the captured deformed pattern are added to the two prestored AC components respectively, two moire fringes only reflect sine and cosine of the object's phase information can be successfully generated via a series of data processing procedures. Finally, the phase distribution of the measured object can be extracted by arctangent of the ratio of these two moire fringes. Compared with computer-generated moire profilometry based on algebraic multiplication, this proposed method can reduce the effect of high frequency noise and residual DC component on measurement and improve the measurement accuracy. While compared with [Formula: see text] phase shifting FTP, this method can measure more complex objects with better measurement capability. Experimental results verify the feasibility and validity of the proposed method.

Dynamic phase retrieval for fringe image processing in moiré tomography

Abstract: The measurement and visualization of transient three-dimensional (3-D) physical parameters (density and temperature) distribution of complex flow fields are critical technologies for the characteristics studies of flow fields in modern energy engineering. Among the optical computed tomography (OCT) methods, Moire tomography has the advantages of simple optical path structure, strong anti-interference ability and wide measurement range, which is especially suitable for complex flow field measurement in noisy environments. Acquiring the transient phase information from the moire projection is of great importance for the dynamic 3-D parameters reconstruction of complex flow fields. In this paper, the dynamic phase retrieve methods including Fourier and spatial phase-shifting in moire tomographic are studied, respectively. In the Fourier method, an adaptive first-order spectrum extraction algorithm for Fourier transform moire fringe and a phase calculation method are proposed. Through this, the projection phase can be obtained directly by multiplying the inverse Fourier transform of the positive first-order spectrum of deformed fringe with the inverse Fourier transform of the negative first-order spectrum of reference fringe. In spatial phase-shifting method, a spatial phase-shifting- interferometry-based moire volume computed tomography (MVCT) method was proposed to extract the radial shearing phase distribution of grid moire fringe. The measured results for the first-order partial derivative of the phase projection of a propane flame both by Fourier and spatial phase-shifting methods in the experimental moire computed tomography systems are presented. The research will be valuable for monitoring the combustion state in energy engineering.

Dynamic effect in the moiré magnifier by using the weak domain transformation.

Abstract: The design of an image with dynamic effect usually adopts an interlacing strategy, but it suffers from the crosstalk between the neighboring images. Here, by introduction of the weak domain transformation to the micro pattern array (MPA), striking motion effects are realized with no crosstalk. A complete theoretical model based on both the moire and fix point theorem is developed for interpretation of the kinetics. A microlens array-based moire magnifier is fabricated to demonstrate the visually striking motion effect. The moire magnifier is of primary interest for a wide variety of applications in appealing decoration, information encryption, and displacement measurement, etc.

Fabrication of moiré on curved surfaces.

Abstract: Moire is an appealing visual effect observable when two or more repetitive patterns are superposed. Fabrication of moire effects has already proven to be useful in a range of applications, from art to engineering. Here, we introduce a method for designing and fabricating level-line moires on curved surfaces. These moire shapes are obtained by superposing a partly absorbing layer and a layer formed by an array of cylindrical lenses or by two layers of cylindrical lenses. We formulate the problem of placing an array of cylindrical lenses on a curved surface as a design problem with a small number of dimensions. The range of possible solutions can therefore be explored by a human observer. We demonstrate the quality of our method by rendered simulations and by fabrication. The resulting static displays can be manufactured using different fabrication techniques, from multi-material 3D printing to molding.

High speed, high accuracy displacement extraction from sinusoidal like Moiré fringes in a novel optical encoding technology

Abstract: Optical encoding technology is one of the most popular technologies with nano-meter degree accuracy in precise displacement metrology field. Basically, two optical gratings overlap in the encoder, resulting in Moire fringes. An optical sensor records the Moire fringes signal. When one of the optical gratings moves, the Moire fringes will vary. The phase of the Moire fringes is extracted from the signal, and the displacement is obtained from the phase. The fabrication always becomes more difficult and the cost is higher when the measurement accuracy becomes higher for such optical encoder. We have developed a simple, novel encoder with only one optical grating and an optical imaging system. The Moire fringe curve is obtained when the optical grating overlaps with two complementary digital gratings which are virtually constructed with a CCD or CMOS sensor in a camera. In this technique, the Moire fringe curve is not a strict sine wave, leading to some difficulty to accurately extract the phase value. This paper compares the performance of four phase extraction algorithms, i.e., Fourier transform, polynomial fitting, Hilbert transform and wavelet transform. The experimental results show that both the measurement accuracy and repeatability of the four algorithms are within 30 nm after calibration. The overall accuracy of the wavelet transform is the best with minimum error of only 5 nm. The processing speed of FFT is the fastest, reaching sub millisecond level.

Deep Learning-based Moiré Pattern Removal from a Single Image: A Survey and Comparative Study

Abstract: Moire pattern in a single image is common in image visual quality degradation induced by frequency aliasing between cameras and monitors when taking a screen-shot photo. It is mainly resulted from the interference between the pixel grids of the camera sensor and the device screen. However, removal of the Moire patterns is challenging based on the complex frequency distribution and imbalanced magnitude in color channels. Only a few studies in the literature focused on the solution of Moire pattern removal from a single image. Traditional studies usually treated the problem as an image denoising problem and applied some filtering or signal decomposition operations based on some image priors (e.g., sparsity). Relying on the rapid development of the deep learning techniques, some deep learning-based approaches of Moire pattern removal have been presented recently. This paper presents a brief survey and comparative study for the recent deep learning-based research works on Moire pattern removal and discusses possible further research directions.

Acoustic Shadow Moiré Interference, Experimental Proof

Abstract: Shadow moire techniques are developed for optical waves to image 3D objects to determine their surface topology. In this paper we prove experimentally that also ultrasound can be used to create moire images. Using moire techniques will enhance ultrasound applications, such as medical imaging and material characterization. In our experiment, we used a grating mask made of aluminum, an ultrasound source in the megahertz range, and an acousto-optic detector to create and capture Talbot images for the grating. Talbot images are captured using and acousto-optic camera. The captured image was created from ultrasound waves with λ=0.43 mm. The fringes of the images proved that they are shadow moire fringes.

Transient digital Moire phase shift interference measuring device and method for surface shape of optical element

Abstract: The invention discloses a transient digital Moire phase-shift interference measuring device and method for the surface shape of an optical element, and the device and method solve a defect that the measurement range needs to be changed through sacrificing the instantaneous vibration resistance when a two-step carrier splicing method is used, expand the measurement range of a conventional digital Moire phase-shift method, and also retain the instantaneous vibration resistance of the digital Moire phase-shift method. The device comprises a light source (1), a spectroscope (2), a reference mirror(3), a first polarization grating (4), a measured mirror (5), a second polarization grating (6), a first imaging objective lens (7), a first camera (8), a second imaging objective lens (9) and a second camera (10). Different carriers are loaded through the light splitting performance of the polarization grating, the two beams of interference light are separated through the polarization grating, and two actual interference patterns are obtained at the same time.

Method and device for removing moire patterns, and image display

Abstract: The invention discloses a method and a device for removing moire patterns, and an image display, which relate to the technical field of image processing, and aim to solve the problem of image distortion when the moire patterns in an image are removed. The method for removing the moire patterns comprises the following steps of: converting a first spatial domain image from a spatial domain to a frequency domain to obtain a first frequency domain image; determining frequency coordinates corresponding to a moire pattern in the first frequency domain image; filtering a frequency domain value at thefrequency coordinates corresponding to the moire pattern in the first frequency domain image to obtain a second frequency domain image; and converting the second frequency domain image from the frequency domain to the spatial domain to obtain a second spatial domain image. The method and the device for removing the moire patterns and the image display provided by the embodiment of the invention are used for image processing.

Use of Moiré fringes in digital holography for optical alignment

Abstract: Moire fringes may be encountered in digital holography when the local fringe period is comparable to the pixel separation of the recording CCD array. In this work, we demonstrate the relation between the transverse misalignment of a lens used in an inline digital holographic system using CW illumination with the position of Moire pattern on the recording CCD plane. A test object such as a one-dimensional opaque block is used along with a single lens imaging system, and the CCD plane is assumed to be in the far-field of the image plane. Our preliminary results show that small transverse misalignments can be tracked by monitoring the location of the Moire pattern. It is proposed that Moire patterns can be used to detect and correct optical misalignments in more complex optical systems.

Transient digital Moire phase shift interference measuring device and method

Abstract: The invention relates to a transient digital Moire phase shift interferometry device and method, which solve the defect that the measurement range needs to be changed by sacrificing the instantaneousvibration resistance when a two-step carrier splicing method is used, expand the measurement range of the traditional digital Moire phase shift method, and simultaneously retain the instantaneous vibration resistance of the digital Moire phase shift method. The device comprises a light source (1), a first spectroscope (2), a reference mirror (3), a polarization grating (4), a measured mirror (5),a [lambda]/4 wave plate (6), a second spectroscope (7), a first line polarizer (8), a first imaging objective lens (9), a first camera (10), a second line polarizer (11), a second imaging objective lens (12) and a second camera (13). Different carriers are loaded through the light splitting performance of the polarization grating, the two beams of interference light are separated through the polarization grating, and two actual interference patterns are obtained at the same time.

Phase information extraction for moiré fringes based on multiresolution analysis

Abstract: In this paper, the multiresolution analysis (MRA) method is used to preprocess moire fringes, which can reduce the number of data points and increase computation speeds. To discuss the applicability of the method, a candle combustion flow field is chosen as an example for experiment by moire deflectometry. First, moire fringes are preprocessed by the MRA method. Then, phase information extraction and refractive index reconstruction are performed on the three-level low-frequency approximation components. Finally, the involved results prove that the calculation time required for phase information extraction and refractive index reconstruction is greatly reduced based on the moire fringes preprocessed by MRA method. The relative error could be accepted if the suitable approximation level is applied.