Showing papers on "Moiré pattern published in 1996"

Interferometric methods and biomedical research

Abstract: Optical metrology based on the principle of interference can be applied as a testing tool in biomedical research. Interferograms in form of fringe patterns can be produced in two-beams interferometers, holographic or speckle interferometers, in setups realizing moire techniques or in deflectometers. By analyzing of the fringe pattern images, information about the shape or mechanical behavior of the object under study can be retrieved. Here, some of the techniques for creating fringe pattern images were presented along with methods of analysis. Possible applications of interferometric methods, especially in the field of experimental orthopedics, endoscopy and ophthalmology will be pointed out.

Theory of Electron Beam Moiré.

Abstract: When a specimen surface carrying a high-frequency line grating is examined under a scanning electron microscope (SEM), moire fringes are observed at several different magnifications. The fringes are characterized by their spatial frequency, orientation, and contrast. These features of the moire pattern depend on the spatial frequency mismatch between the specimen grating and the raster scan lines, the diameter of the electron beam, and the detailed topography of the lines on the specimen. A mathematical model of e-beam moire is developed that expresses the spatial dependence of the SEM image brightness as a product of the local intensity of the scanning beam and the local scattering function from the specimen grating. Equations are derived that give the spatial frequency of the moire fringes as functions of the microscope settings and the spatial frequency of the specimen grating. The model also describes the contrast of several different types of moire fringes that are observed at different magnifications. We analyze the formation of these different fringe patterns, and divide them into different categories including natural fringes, fringes of multiplication, fringes of division, and fringes of rotation.

Moire interferometry system and method with extended imaging depth

Abstract: A moire interferometry system and method are provided for achieving full field surface contouring with an extended depth of view of image. The moire interferometry system includes a projection system generally made up of a light source, imaging lens and a square wave grating pattern. The imaging lens is configured to filter higher order light rays passing through the square wave grating pattern so as to project a sine wave like pattern onto a desired surface. The moire interferometry system also includes a viewing system generally made up of an imaging lens, a submaster grating and a camera. The submaster grating is preferably a customized grating that may be produced by recording a grating pattern in relation to a reference surface. The camera is able to view an image anywhere within the extended depth of image and analyze the moire fringes. A determination of deviation between a test part and a reference surface provides a part inspection system.

Noise-free normalized fringe patterns and local pixel transforms for strain extraction

Abstract: Noise reduction is one of the most exciting problems in automatic fringe processing. We propose a two-dimensional (2-D) envelope transform for normalization of fringe patterns, coupled with spin filtering, to construct so-called noise-free normalized fringe patterns. The 2-D envelope transform uses correct fringe intensity envelopes for normalization of fringe patterns, i.e., for making the fringe background and amplitude constant over the whole field. Spin filtering is applied to fringe patterns for removal of random noise taking into account fringe flow. With spin filtering and the 2-D envelope transform, a noise-free normalized fringe pattern is constructed for postprocessing. Based on this improved fringe pattern, two local pixel transforms for strain extraction from a single moire pattern are developed, in which the digital pure secondary moire method is improved and the strain-field image method with division is developed.

Lens focus shift sensor

Abstract: A focus shift sensor includes a light source which directs light through a first grating to form a pattern of light. The pattern is directed through the lens which images the pattern at a second grating. The two gratings have different periods such that the second grating generates a pattern of Moire fringes which are projected onto a CCD array. The second grating is preferably tilted with respect to the plane of the image of the pattern from the first grating such that only a portion of the second grating is within the range of focus of the lens. As a result, a pattern of shortened Moire fringes is produced. As the range of focus shifts along the second grating, the Moire fringes move along the CCD array. The movement of the fringes is tracked and the system is adjusted to maintain the location of the focal plane of the lens at a desired location.

Analysis and reduction of moire patterns in scanned halftone pictures

Abstract: In this dissertation we provide a comprehensive theory for the formation of a moire pattern in a sampled halftone image. We explore techniques for restoring a sampled halftone image with a moire pattern and techniques for preventing a moire pattern when a halftone picture is scanned. Specifically, we study the frequency, phase, and spatial geometry of a moire pattern. We observe and explain the half period phase reversal phenomenon that a moire pattern may exhibit. As a case study, we examine the moire patterns generated by a commercial scanner. We propose three restoration methods, including a notch filtering method, a simulation method, and a relaxation method. We also describe a moire prevention method, the partial inverse Fourier transform method. Finally, we propose a research agenda for further investigation.

X-ray Moiré Topography on SIMOX Structures

Abstract: Moire fringes are observed on X-ray diffraction topographs of silicon on insulator structures produced by different SIMOX (separation by implantation of oxygen) processes. The parameters that can be extracted from a diffraction Moire experiment are discussed. A Moire experiment is sensitive to the relative strain between the two parts of a bicrystal system. The sign of the relative strain and its components perpendicular to the sample surface cannot be determined from the geometry of the Moire fringes. The influence of sample curvature on Moire fringes is considered. Different deformation models are discussed to interpret the experimental findings. It is found that a triclinic relative deformation explains the observed symmetries between Moire topographs from different reflections, the spacings of the Moire fringes and their angles to a reference direction. Both the dilational and the shear components of the relative strain tensor are found to be in the order of 10 -7 . Significant differences in relative strain are observed on SIMOX samples produced by different processes.

Inspection system of flat panel display

Abstract: PROBLEM TO BE SOLVED: To suppress an interference fringe by a method wherein when a detec tion element is spatially and periodically positioned on first and second positions to display an image, a signal including a first moire image interference fringe is detected on the first position, next a signal including a second moire image is detected and intensity levels of both of the signals are averaged at a sampling point. SOLUTION: A high resolution CID camera 15 covers a whole region of a display panel 11. A line 32 of an output of the camera 15 is applied to an image-processing computer 34 that operates the signal of the camera 15. In order to judge the uniformity of luminance of the display panel, the inspection of the first time is executed at the first time of alignment of a panel image with a camera pixel array. Generated intensity signals are stored in a memory of a computer 36. The image is slightly shifted with respect to a camera detector pixel because of the physical shift of the display or camera optical system, then the other image of the panel is detected to be stored in the memory. Moire interference fringes are different with each other. The image detection is executed on various shift positions and the interference fringe is suppressed.

Technique for detecting particles on a wafer support surface

Abstract: A method of detecting particles on a wafer support surface comprising positioning a wafer in a first position on the surface with the wafer in the first position, generating a first pattern on the wafer, and moving the wafer. Then, after moving the wafer, generating a second pattern on the wafer to generate a moire pattern by the interaction of the second pattern with the first pattern. The moire pattern is inspected to identify any visual distortion in the moire pattern due to physical distortion of the wafer caused by a particle on the support surface during the generation of the first pattern. The patterns may be ruled parallel lines, and the second pattern may be moved during inspection to shift the moire pattern to reveal distortions over a wide area.

Multiaperture overlap-scanning technique for moire metrology

Abstract: Multi-aperture overlaj)-scanning technique for moire metrologyMing-yi Chen and De-zhu WuShanghai University, Lab of Optics & MetrologySouth Gate, Jiading Shanghai 201800, PR ChinaPhone: (21) 5952-8508 Fax: (21) 5952-9932ABSTRACT1ii moire technique there are some inherent drawbacks such as: inevitable shadow in illumination and readout ,limiteddepth and size of measurement which obstruct its further application in topographic measurement of large object, especiallywith complicated shape. Our studies show that the nmlti-aperture overlap-scanning technique (MAOST) can also be appliedto moire method. Therefore, not only all these drawbacks can be removed, the problem sensitive to eccentric positioning ofobject and axis swing of the turntable in 360 profilometry can also be overcome. In this paper the mathematical mode! forMoire pattern transformation and connection is described, and results of simulation tests are presented.Keywords: multi-aperture overlap-scanning, pattern transformation and connection, irioi re inetrology.1. INTRODUCTIONIn optical metrology moire technique is a versatile approach which has been widely applied to solve both scientific andindustriial problems. Though it is a well developed technique, it still has some inherent drawbacks to be overcome such as:limited depth and size of the measurement, inevitable shadow of illumination and dead area of readout, etc. Moreover, 360profilometr' has become a hot subject since early 80's 1,2

Curvature contours of flexed plates by a multiple illumination moiré shearing interferometer

Abstract: A new moire method is proposed to map partial slope, partial curvature and twist curvature contours of laterally loaded specularly reflecting plate models. Converging HeNe laser light is diffracted by a lens plane cross grating, different combinations of orders are selectively permitted through the Fourier transform plane and collimated to illuminate the plate model. This technique eliminates the difficulties involved in Fourier filtering in the imaging optics, thereby extending the reflection moire’ interferomelry to general plate structures and loading. The slope contours are obtained still by double exposure.

Application of a birefringent lens in photoelastic studies using a coherent moire technique

Abstract: In photoelastic investigations, one uses the property of stress induced birefringence for stress analysis. Normal polariscopes are used for such studies. However, the accuracy of the methods is low. For better accuracy, interferometric and holographic methods are generally used. Holography, along with a shearing technique, is also used to obtain partial derivatives of displacement with respect to spatial co-ordinates. In these methods, the resultant fringe pattern is obtained from the mutually shifted holograms and the generation of such patterns requires four exposures altogether. The present paper represents a method based on a coherent moire technique for studying the first derivative of a stress pattern using birefringence properties. The analysis seems to be very similar to holographic techniques as both produce second order fringes. The advantage of this method is that it requires only one exposure. The basic principle as well as some experimental results are presented.

Laser beam scanning optical apparatus having means for generating moire fringes

Abstract: A laser beam scanning optical apparatus which has Moire fringes generating elements which is located near a position optically equivalent to a scanning surface and modulates a laser beam emitted from a laser source to generate Moire fringes. The Moire fringes generating elements comprises, for example, a first filter which has spatial grating and a second filter which has spatial grating which slants slightly with respect to the spatial grating of the first filter, the first filter and the second filter being arranged upstream and downstream respectively in an optical path. The laser beam scanning optical apparatus further has a light receiving element for receiving the Moire fringes generated by the Moire fringes generating elements. Focusing means for correcting a position of an image point of the laser beam is driven in accordance with an output of the light receiving element. For example, the light receiving element is a photoelectric element with a plurality of light receiving surfaces, each of which generates an electric signal in accordance with the laser beam incident thereto, and from a phase difference between the electric signals, the position of the image point is detected.

Analysis of moire patterns in non-uniformly sampled halftones

Abstract: We analyze the moire patterns in halftone images scanned by a popular commercial scanner. We show that the non uniform sampling scheme employed by the scanner introduces extra aliasing components compared to uniform sampling and thus complicates the moire patterns formed. The analysis applies to other scanners that employ non uniform sampling. We also suggest methods for suppressing the moire patterns in scanned halftones.

The application of two-refractive-index contouring on the contour difference of two compared specimens

Abstract: The development of comparative holographic Moire interferometry is accelerated by the need for nondestructive evaluation. It is based on a comparison of a master and test objects and a visualization of the difference in the mechanical responses under identical loading condition. In this paper, the hybrid method of comparative holographic Moire interferometry and the two-refractive-index contouring technique are used to generate contour difference for two compared specimens. The interference pattern of the master and test specimens are superimposed by a reconstruction beam. Moire fringes, produced between the two interference patterns, outline the contour differences in the compared specimens. The proposed experimental approach provides an advantage that full knowledge of the optical arrangement during construction and reconstruction of the hologram does not have to be accurately available. A partial-spherical object and its rotated status were simulated as the master and test objects.

Fast algorithms for automatic moire fringe analysis: application to noncontact measurements for quality control of industrial components

Abstract: Moire methods are optical methods that are based on the effect of superposition of grating lines and have been widely used in the context of industrial applications for shape analysis, for non-contact measurements, and for quality control of industrial components. In applications the following computations: image filtering, fringe skeletonizing and fringe numbering have to be performed for each test object, before comparison between the numerically reconstructed test object shape and its CAD model. In order to reduce the computing time required by the preceding computations, the inverse moire technique has been introduced by Harthong. Instead of using a grating made of parallel straight lines, the inverse moire technique uses a pre-computed specific gratin, that is formed of curved lines such that the moire pattern is composed of parallel straight fringes if the test object shape is conformed to its CAD model. Defects are then characterized by a deformation and a curvature of these parallel fringes. In this paper, we present examples showing that standard fringe extraction by automatic thresholding is not that easy. To overcome this difficulty, we propose a four stage process algorithmical approach that allows fringe detection in inverse moire images with high sensitivity and specificity. First we used the well-known image processing technique called unsharp masking, to enhance moire image and to emphasize low contrasted fringes. The second step is to extract bright fringes by image segmentation and constrained contour modeling. After detection of these bright fringes inside the zone of interest of the moire image, we get the thick skeleton of adjacent background and of dark fringes. The third step is to skeletonize this thick skeleton of adjacent background and of dark fringes, using morphological thinning of well-composed sets, that assures that each fringe skeleton will be one pixel thick, at the difference of standard thinning techniques. The fourth step is to apply a graph technique to isolate the individual dark fringes. When all these four steps have been followed, one is left with a binary image showing the dark fringe pattern skeleton. The experimental results that have been obtained have shown the robustness of this algorithmical approach, for the analysis of noisy inverse moire images.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Alignment method for moire fringe analysis

Abstract: PURPOSE: To provide an alignment method in which a measurement to analyze the uneven shape on the surface of an object to be inspected can be performed easily by a method wherein the inclination of the object is adjusted in such a way that the surface of the object becomes nearly parallel to a moire lattice face. CONSTITUTION: Moire fringes which are generated between the moire lattice face of a moire lattice 11 and the face of an object 12 are imaged, and the shape of the face is analyzed on the basis of the obtained image of the moire fringes. The shape of the obtained face is approximated a shape on a prescribed plane by using the least squares, and the coordinate value of a height Z in prescribed four positions in the plane is obtained. Then, on the basis of respective x, y and z coordinates in the respective positions, actual inclination in the vertical direction and the horizontal direction of the plane to which the face is approximated are obtained. Then, inclinations to the x-axis and the y-axis of a stage 13 are adjusted, and the face of the object 12 on the stage 13 and the lattice face of the lattice 11 are set so as to be parallel to each other. Thereby, the uneven shape of the face is analyzed with high accuracy in a state that it is aligned and adjusted.

Design of an optical level using the Talbot effect

Abstract: An optical arrangement for liquid-level measuring is proposed. The method is based on self- imaging or Talbot effect. Knowing the container dimensions of a liquid, it is possible to obtain the volume changes by the liquid variation in the container. The optical arrangement consists in detecting a diffraction field of a Ronchi grating illuminated by a collimated beam. This field is first reflected by the interface liquid-air, afterwards casting on a second Ronchi grating. This superposition produces a Moire pattern when the Talbot plane of the first grating coincides with the second one. If the travelled path of the wavefront is not a Talbot distance, the Moire pattern is lost. In this way, it is necessary to move the second grating up to see the sharper Moire fringes. The grating change gives directly the level change. Description of the experimental setup and results are shown. Strengths and weaknesses of the method are presented. The future lines of work are given in order to have an automatic and compact instrument.

Holographic illumination for comparison in interferometry

Abstract: Conventional holographic interferometric and speckle pattern interferometric techniques are tailored basically to compare the two states of the very same object, which may have optically rough surface or optically distorting transparent walls around. The direct comparison of the behavior of two different--but macroscopically quite similar--objects does not fit naturally in the process. At present, this type of extension can go three different ways. In holographic interferometry, one can mix the interferograms of the two objects at some sublevel of interferogram making and the moire effect of the individual fringe systems can be produced. In speckle pattern interferometry, the reference surface can be replaced by the other object itself and it serves as a live reference: changing according to the test object. Finally, although really first if time of birth is regarded, holographically recorded and reconstructed images of a master object can be used for illumination of test objects--in an otherwise conventional holographic or speckle interferometric arrangement. The present paper deals with this latter technique. Some new developments are reported in difference holographic interferometry and partly as a consequence of this--a really successful realization is introduced in holographically illuminated difference ESPI.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Surface evaluation combining the moire effect and phase-stepping techniques in Fizeau interferometry

Abstract: The usual phase-stepping algorithms are employed to evaluate the phase of Fizeau interferograms in topographic measurements. The superposition of the interferogram with a Ronchi grid provides a Moire pattern. The phase modulation is obtained by the in plane displacement of the grid, while a sinusoidal intensity pattern is obtained by defocusing the image acquisition system. In this work, the measurement range of the method in the function of the maximum variation of height surfaces is calculated and verified.

Automated Talbot interferometer using Moire fringe scanning and ray tracing

Abstract: An automated Talbot interferometer using Moiré fringe scanning and ray tracing is proposed. Our novel method can obtain the wavefront aberration by a phase object on the plane where the object itself is situated.

Optical sensor and optical apparatus using the same

Abstract: In an optical apparatus utilizing moire fringes to inspect surface irregularities of a test object, a single light beam forms a light beam network in an optical sensor (28) such that the test object can be two-dimensionally detected, thereby preventing the test object from abnormally approaching a moire grating (12). The light beam is reflected between a pair of mirrors (50, 52) a plurality of times within an identical plane and then the optical sensor (28) detects the intensity of the light beam. The optical sensor (28) is disposed such that the light beam network is positioned directly below the moire grating (12). Accordingly, a test object (2) abnormally approaching the moire grating (12) can be two-dimensionally detected by the light beam network, thereby improving the accuracy in detection.

Active stabilization and real-time analysis of interference fringes

Abstract: An active two-beam interferometer has been developed which locks fringes in the presence of external perturbations such as vibration and air flow and enables measurement on an unstabilized table. Movement of carriered fringes caused by the perturbations are detected by a spatial filtering detector whose output signal is fed back to injection current of a laser diode to compensate for path variations by the resulting wavelength shift. The video image of the fringes is supplied to a real time fringe analyzer which delivers the phase distribution at the video rate. The analyzer is based on electronic moire principle for simultaneous generation of three phase shifted fringe patterns. The results from a spherical mirror of 130 mm- diameter have shown good coincidence in spherical errors with that obtained from measurement on an optical bench. Only its repeatability proved to be worse by 1.7 times.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Method and instrument for measurement using moire method

Abstract: PURPOSE: To provide a measuring method, etc., by which the three-dimensional shape of the surface of an object to be measured can be measured with high accuracy by making the phase shifting method applicable to the Moire method. CONSTITUTION: A laser beam B is set so that the beam B can get in Moire fringes having one measuring depth by means of optical interferometers BS1 , M3 , M4 , and BS2 after the beam is enlarged by means of a beam expander L1 and collimator L2 . The laser beam formed into a state of interference fringes is split into two laser beams by means of a beam splitter BS3 and one laser beam B1 is projected upon the surface of an object O through a phase shifter OP2 . Then Moire fringes formed on the surface of the object O by projecting the other laser beam B2 superposing on the beam B1 and another Moire fringes similarly formed on the surface of the object O by shifting the phase of the Moire fringes by means of a phase shifter OP2 are detected by means of a photodetector element, and the phase shift between the Moire fringes at the part is obtained by performing arithmetic operation on the luminance at each point on the photodetector element detected several times and a picture is displayed by means a displaying means based-on the phase shift and position of the photodetector element.

Precise measurement of linear displacement by moire fringes of elongated circular gratings

Abstract: Moire fringes of elongated circular gratings to precisely measure the linear displacements are presented. The moving direction of a grating can be easily determined and the moving displacement can be measured within the accuracy of 1/10 pitch of the grating by using moire fringes of elongated circular gratings.

Moire Patterns in Scanned Halftone Images

Abstract: In this report we examine the origin of moire patterns that occur when scanning halftone images. By analysing the halftoning and sampling processes in the frequency domain we find that halftone Images typically have spectral copies of the baseband in the high frequencies, and the moires are aliases of these generated by the sampling. We analyse the kind of effects that are generated for monochrome and color halftones and scanners. We discuss how moire effects may be detected and eliminated in an automatic fashion.