Showing papers on "Moiré pattern published in 1989"
Patent•
23 Oct 1989
TL;DR: In this article, a printed image (It4) is produced with halftone images for respective color printers while so-called rosette moire and a color shift from an original image are prevented.
Abstract: OF THE DISCLOSURE A printed image (It4) is produced with halftone images for respective color printers while so-called rosette moire and a color shift from an original image are prevented. Halftone dots (Hm4, Hc4, Hk4) linear shapes extending in respective prescribed directions, thereby forming parallel lines with respective intervals (dm4, dc4, dk4). These extensional directions and intervals of parallel lines are so established that they effectively prevent the rosette moire and the color shift.
68 citations
TL;DR: In this paper, the authors presented one-dimensional strain analysis by a moire method using a Fourier transform and extended it to two-dimensional analysis by introducing digital image processing.
Abstract: Formerly, the authors presented one-dimensional strain analysis by a moire method using a Fourier transform. In the present work, the method is extended to two-dimensional strain analysis. The analysis is completely automated by introducing digital image processing. All of the laborious and subjective procedures required in the classical and conventional moire method, such as separation of the two gratings, fringe-sign determination, fringe ordering and fringe interpolation, are completely eliminated; and objective, fast and accurate analysis can be made.
54 citations
TL;DR: In this article, a 150 lines mm-1 specimen grating is imaged onto a reference grating with a specially modified camera lens and the resulting real-time moire fringes are recorded with a high speed image converter camera.
Abstract: The techniques of high resolution moire photography and high speed photography have been combined to allow simultaneous measurement of both in-plane components of a transient displacement field with microsecond time resolution. A 150 lines mm-1 specimen grating is imaged onto a reference grating with a specially modified camera lens. The resulting real-time moire fringes are recorded with a high speed image converter camera. An automatic fringe analysis technique based on the 2-D Fourier transform method is used to extract the displacement information from the high speed sequences. The techniques are illustrated by the results of an investigation into the transient deformation of polymethyl methacrylate caused by solid particle impact.
36 citations
TL;DR: In this article, the carrier fringes are applied to obtain the desired data in complex laminated composite specimens, with procedures that are easier and more accurate than those using loadinduced fringes alone.
Abstract: Practical applications in which carrier fringes are used with moire interferometry for strain measurements are presented. Examples illustrate how moire carrier fringes are applied to obtain the desired data in complex laminated composite specimens. In many cases, carrier fringes permit extraction of much more detailed information, with procedures that are easier and more accurate than those using loadinduced fringes alone. The fringe vector for carrier fringes is introduced and its application to the interpretation of fringe patterns is explained. In moire interferometry, the carrier fringes are produced easily by adjustments of optical elements that control the virtual reference grating.
30 citations
TL;DR: Analytical expressions describing the moire fringes formed by two periodic structures consisting of the evolutes of a circle are derived.
Abstract: Analytical expressions describing the moire fringes formed by two periodic structures consisting of the evolutes of a circle are derived. The circular and radial moire patterns can be formed by contact and noncontact superimposition of the structures. In the latter case the self-imaging phenomenon is used. Experimental verification and proposals for use are given.
26 citations
TL;DR: With an appropriate selection of the scan frequency and screen angle for a given screened image, moire beat frequencies in the scanned image can be reduced to a subvisible level without the need for scanning at extreme scan frequencies or postscan image processing.
Abstract: Unacceptable moire distortion may result when images that include periodic structures such as halftone dots are scanned. In the frequency domain, moire patterns correspond to visible aliased frequencies. In the spatial domain, moire patterns are evident as cyclic changes in the size of halftone dots, producing visible periodic "beat" patterns. Moire pattern formation depends on the following factors: (1) the halftone screen frequency, (2) the scan frequency, (3) the angle between the scan direction and the halftone screen, (4) the scanner aperture size and shape, (5) quantization errors from the thresholding operation, (6) scanner and printer noise, and (7) the ink flow in the paper during printing. This paper analyzes the visibility of moire patterns in terms of these factors. In addition, the paper describes an approach to reducing the visibility of moire patterns by directly manipulating the moire formation factors. With an appropriate selection of the scan frequency and screen angle for a given screened image, moire beat frequencies in the scanned image can be reduced to a subvisible level. This approach thereby achieves moire reduction without the need for scanning at extreme scan frequencies or postscan image processing. The strengths of this ap-proach are (1) no data volume increase due to high frequency scan and (2) no need for time-consuming postscan processing. Computer-simulated and actual scan images are presented to illustrate the approach.
21 citations
16 Jan 1989
TL;DR: A new method of contouring 3-D objects in real-time by making use of Digital Speckle Pattern Interferometry (DSPI) alongwith an in-plane sensitive optical configuration is suggested.
Abstract: A new method of contouring 3-D objects in real-time is suggested. The technique makes use of Digital Speckle Pattern Interferometry (DSPI) alongwith an in-plane sensitive optical configuration. The contour interval can be varied in real-time by varying the tilt applied to the object. The variation of the contour interval with the tilt angle and the angle between the illumination beams is discussed. The decorrelation of speckle pattern due to tilt and consequently the disappearance of the fringes is also discussed. Experimental results have been presented for a variety of objects.© (1989) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
20 citations
TL;DR: In electronic imaging detectors using microchannel plates, the mismatch between the pixels on a square mesh and the microchannels on a hexagonal mesh produces moire image defects, which will not be properly corrected by dividing by the flat field image.
Abstract: In electronic imaging detectors using microchannel plates, the mismatch between the pixels on a square mesh and the microchannels on a hexagonal mesh produces moire image defects. Theoretical statistical estimates of the sizes of the microposition offsets and the flat field intensity errors are calculated, showing the trade-off between resolution and position accuracy. A distinction is made between moments of spot images and moments of the single-pixel-response functions. As the resolution between the hex and square meshes is improved, the detector resolution is improved, but at the expense of an about 10 percent moire pattern. These moire patterns will not be properly corrected by dividing by the flat field image.
19 citations
Patent•
22 Dec 1989
TL;DR: In this article, a process for observing moire patterns of surfaces to be tested by applying the moire method using phase shifting is described. And the object gratings to be observed are pictured onto auxiliary gratings and the generated patterns are detected, stored and/or processed by computer, wherein for each observation at least phase-shifted patterns are respectively evaluated.
Abstract: The object of the invention is a process for observing moire patterns of surfaces to be tested, wherein the object gratings to be observed are pictured onto auxiliary gratings and the moire patterns generated thereby are detected, stored and/or processed by computer, wherein for each observation at least phase-shifted moire patterns are respectively evaluated. Furthermore, the invention relates to a device for observing moire patterns of the surfaces to be tested by applying the moire method using phase shifting. For an observation of the phase-shifted moire patterns associated with the object grating are simultaneously generated, pictured and detected by superposition of the object grating image with auxiliary gratings which are disposed in a phase-shifted manner.
17 citations
TL;DR: The authors present a physical description for the production of time-averaged moire fringes involving the splitting of grid lines resulting from their behavior as simple harmonic oscillators.
Abstract: Time-averaged moire fringes may be produced by projecting a grid onto a vibrating test item surface using a conventional (2 in. x 2 in.) slide-projector and recording with a 35-mm SLR camera. Quantitative analysis of the resultant fringes is generally performed with the help of equations developed by time-averaging the optical intensity of the projected grid throughout the vibration period of the test item surface. In the present paper the authors present a physical description for the production of time-averaged moire fringes involving the splitting of grid lines resulting from their behavior as simple harmonic oscillators. Superimposition of vibrating grid lines produces blurring of the photographic image; regions of zero-amplitude vibration (nodes) may be identified by the clarity of their grid lines, enabling the analysis of mode shapes from the photographs.
16 citations
TL;DR: In this paper, the authors proposed a method for the detection of defects based on a comparison of the responses of two macroscopically identical specimens. But the method is contactless and is not suitable for non-destructive quality assessment of mechanical parts.
Abstract: The development of comparative holographic moire interferometry is accelerated by the need for nondestructive testing. This paper describes a holographic moire technique for the detection of defects that is based on a comparison of the responses of two macroscopically identical specimens. At identical loading of the master and test objects, the moire fringes obtained are areas of equal differences in the mechanical responses, and they form closed curves around the defect. The schemes of additive and multiplicative moire are studied experimentally, and their advantages and disadvantages are discussed. Comparison of the suggested technique with conventional holographic interferometry shows its reliability for localizing defects. The comparative method is contactless and is especially appropriate for nondestructive quality assessment of mechanical parts.
TL;DR: Three fringe multiplication methods are proposed which use a digital image processing technique to multiply various interferometric fringes, easy to handle and greatly improve the measurement accuracy.
Abstract: Holographic moire fringes can be multiplied by using diffraction interferometry, an approach which is not applicable to some other interferometric techniques such as geometric moire. Three fringe multiplication methods are proposed which use a digital image processing technique to multiply various interferometric fringes. These methods are easy to handle and greatly improve the measurement accuracy. They enlarge the testing range for applying the interferometric techniques.
Patent•
27 Feb 1989
TL;DR: In this paper, a plurality of grained screen patterns that are different from each other are stored in a general screen pattern memory and accessed at random in response to an address signal (AGP) generated in a random number generator.
Abstract: A plurality of grained screen patterns that are different from each other are previously stored in a grained screen pattern memory. The grained screen patterns are accessed at random in response to an address signal (AGP) generated in a random number generator. An original image data is compared with the random arrangement of the grained screen patterns for each pixel, to produce a halftone dot image. The halftone dot image thus obtained has no periodic distribution of density, such as a moire.
TL;DR: A simple new method of automatically reconstructing the 3-D surface of an object from 2-D moire patterns is proposed, which can automatically and accurately obtain phase value at every pixel point without assigning fringe orders and interpreting data in the regions between fringes by using a discrete cosine transform based algorithm.
Abstract: A simple new method of automatically reconstructing the 3-D surface of an object from 2-D moire patterns is proposed. The method can automatically and accurately obtain phase value at every pixel point without assigning fringe orders and interpreting data in the regions between fringes by using a discrete cosine transform based algorithm, which is free from errors caused by the higher harmonic components, the variation of dc light level, and the modulations of amplitudes on a fringe pattern. The method is capable of fully automatic distinction between depression and elevation on an object surface. Theoretical analysis and experimental verification are presented.
TL;DR: In this article, the authors proposed and experimentally verified two approaches, namely phase shifting of the carrier interference pattern and auxiliary carrier fringe generation with subsequent optical filtering, for additive and multiplicative CHMI.
Abstract: Comparative holographic moire interferometry (CHMI) permits defect detection by comparison of the mechanical responses of two macroscopically identical specimens at equal loading. In the present work a technique of moire fringe separation is suggested that is amenable to automatic readout. Two approaches are proposed and experimentally verified: phase shifting of the carrier interference pattern and auxiliary carrier fringe generation with subse-quent optical filtering. The phase shifting method is applicable to an additive moire scheme with two reference beams. Auxiliary carrier fringe generation can be used in both additive and multiplicative CHMI. The frequency constraints of the latter method due to the optical recording arrangement and mechanical responses of the tested specimen are analyzed.
TL;DR: Experimental results show that this procedure can be successfully applied to shadow moiré topography and does not require object surface continuity.
Abstract: A method for automatically determining in real time the absolute order of shadow moire fringes is developed. The intensity variations on an object surface caused by a light source moving with constant speed are analyzed by fast-Fourier-transform methods. Experimental results show that this procedure can be successfully applied to shadow moire topography and does not require object surface continuity.
TL;DR: A CAD-integrated system using a CCD camera and a digital image processor for 3-D machine vision applications to industrial inspection of CAD-generated master objects is described.
TL;DR: In this article, the form of CAD generated objects is measured in this way by comparing the grid obtained on the surface with a grid which is generated using the CAD surface data, and the difference in form of nominally identical objects by adding or subtracting the observed grids on the two components.
Abstract: The topography of a complex surface can be measured by projecting a light pattern onto it and examining the moire fringes which are obtained when the image of the object is compared with a reference grid. It is possible to measure the difference in form of nominally identical objects by adding or subtracting the observed grids on the two components. The form of CAD generated objects is being measured in this way by comparing the grid obtained on the surface with a grid which is generated using the CAD surface data.
TL;DR: The fringe characteristics in four-beam cross-grating interferometers, illuminated by a source at finite distance, are analyzed and the spatial irradiance distribution of the illuminating source which is separable in two orthogonal directions can be synthesized.
Abstract: The fringe characteristics in four-beam cross-grating interferometers, illuminated by a source at finite distance, are analyzed. From the measurements of the fringe visibilities and the fringe shifts on discrete planes, the spatial irradiance distribution of the illuminating source which is separable in two orthogonal directions can be synthesized. When the line structures of the two cross gratings are not parallel, the fringe pattern has lower contrast which suggests that four line gratings should be used to replace the second cross grating in order to have high contrast fringes. The possibility of forming cross-gratinglike patterns using either a combination of one cross grating and two line gratings or a combination of two line-grating interferometers is discussed. Finally, moire interferometry using a cross-grating interferometer is suggested.
20 Nov 1989
TL;DR: In this paper, the authors used a CCD array to improve the sensitivity of the strain sensor for most elastic strain measurements, since the change in diffraction angle is very small and therefore the sensitivity can be improved.
Abstract: The Moire Interferometric Strain Sensor (MISS) is based on the principle that gratings diffract light in preferred directions determined by their frequency. Hence by tracking the change in diffraction angle the frequency of the grating can be determined. In engineering applications, a grating attached to the specimen would change frequency as a consequence of the strain at that point. Thus the change in diffraction angle can directly be related to strain. Since for most elastic strain measurements the change in diffraction angle is very small, this paper describes the use of a CCD array to improve the sensitivity.
16 Jan 1989
TL;DR: Moire interferometry in this paper is extended to topographic contour measurement of an arbitrary object and has a very high sensitivity which can be the order of Amm.
Abstract: Moire interferometry in this paper is extendedto topographic contour measurement of an arbi-trary object. The principle of the proposed methodis different from that of projection moire and shadowmoire methods in both the moire fringe formingmechanism and the w displacement evaluation.The advantage of the present method over the oth-ers is that it has a very high sensitivity which canbe the order of ymm. As an experimental verifi-cation, the method is applied to the topographiccontour measurement of a cylindrical shell withand without a diametric point loading. 1 Introduction In applied mechanics and engineering prac-tice, a knowledge of topographic contour is of-ten required. The existing methods for measur-ing topographic contour include the shadow moiremethod,' the projection moire method,2 the holo-graphic method,' the laser speckle method4 andsome other methods. The main disadvantage ofthe shadow moire method is the lack of sensitiv-ity; of the projection moire and the holographicmethods, the sophisticated optical arrangement;of the laser speckle method, the poor fringe qual-
TL;DR: In this article, an extension of moire holography for structural analysis on reinforced plate models is presented, where unequal optical paths, caused by lack of uniform thickness, are compensated for and do not alter the moire fringe patterns.
Abstract: This paper deals with an extension of moire holography for structural analysis on reinforced plate models. It is shown that unequal optical paths, caused by lack of uniform thickness, are compensated for and do not alter the moire fringe patterns. Moreover, a simple technique is described for replicating high-sensitivity moire gratings on Plexiglas models. The validity of the method has been satisfactorily tested on plate models with different geometries.
01 Jan 1989
TL;DR: In this paper, double exposure moire photographs of cracks moving through plates of polymethylmethacrylate (PMMA) were recorded with a rotating mirror camera at 2 μs frame-level.
Abstract: The use of moire photography as a technique for measuring the dynamic displacement field, and dynamic stress intensity factor(KId) of a fast crack has been investigated. Sequences of double exposure moire photographs of cracks moving through plates of polymethylmethacrylate (PMMA) were recorded with a rotating mirror camera at 2 μs frame–1. One sequence was analysed in detail to reveal the time variation of both in-plane displacement components, and KId. The paper ends with a description of a high resolution moire apparatus, capable of resolving 150 lines mm–1; preliminary results from quasi-statically loaded cracks are presented.
Patent•
05 Sep 1989
TL;DR: In this article, a reference grating is projected on the object of measurement from a projector and its deformed grating image is picked up by a television camera, which is passed through an A/D converter and a noise removing filter 34 and the grating pattern signal of a grating patterns generator 35 are multiplied by a multiplier 36 to form moire fringes.
Abstract: PURPOSE:To reproduce an object three-dimensional shape faithfully by generating nodes corresponding to the curvature of a contour line based upon contour line information, and connecting nodes at short distances among the nodes and representing a wire frame model. CONSTITUTION:A reference grating is projected on the object of measurement from a projector 31 and its deformed grating image is picked up by a television camera 32. The deformed grating image signal which is passed through an A/D converter 33 and a noise removing filter 34 and the grating pattern signal of a grating pattern generator 35 are multiplied by a multiplier 36 to form moire fringes. The moire fringes are passed through a low-pass filter 37 and converted by a threshold value processing part 28 into a binary signal, which is passed through a line thinning processing part 381 and a degree decision processing pat 39; and a node generator 40 generates noses on the moire fringes according to the curvature of each moire fringe, a node connection processing part 41 connects adjacent nodes (same moire fringes and adjacent moire fringes), and a three-dimensional shape reproduction part 42 outputs the wire frame model.
TL;DR: A “Dual Sampling Method (DSM)” is proposed, which can effectively suppress the moire fringes by carrying out twice sampling procedures with different sampling ratio.
TL;DR: In this article, a non-destructive method using no special markers to measure distortions in gratings, which is useful in the fabrication process as a monitoring procedure, is presented, which consists of a comparison of a part of the grating which is used as a reference, with an other part of same grating.
01 Jul 1989
TL;DR: In this paper, the authors compare the performance of cross-grating and sampled grating and show that while crossed gratings can correctly predict the frequencies of sampled grates, they cannot correctly predict their amplitudes.
Abstract: : Traditional 'crossed-grating' moire, as well as newer 'sampled-grating' (scanning) moire, have proven to be effective methods of shape measurement. There is speculation that the moire patterns of a sampled grating, which are due to aliasing, can be modeled with crossed gratings. We compare the two and show that while crossed gratings can correctly predict the frequencies of a sampled grating, they cannot correctly predict the amplitudes. We go on to formulate a new model which accounts for multiple stages of sampling and transmission, and show how neglecting multiple stages can lead to mistakes in moire analysis. We demonstrate our model with an experiment using a digital imaging system. (RRH)
Patent•
31 Jan 1989
TL;DR: In this article, the rotating angles of a flywheel are measured by confronting one end surfaces of multi-core optical fibers which are spaced a small distance from each other in a movable manner, thereby to observe moire fringes generated at the other end surface of the fiber.
Abstract: PURPOSE:To measure physical quantities of an object such as length, angle, distortion, etc. with ease and high accuracy, by confronting one end surfaces of multi-core optical fibers which are spaced a small distance from each other in a movable manner, thereby to observe moire fringes generated at the other end surface of the fiber. CONSTITUTION:In the case where the rotating angles of a flywheel 10 is desired to be measured, an image fiber 2 is fixed to the flywheel 10 while the flywheel 10 is illuminated by a light source 1. Another image fiber 3 is confrontingly provided several mum away from one end surface of the image fiber 2. Many cores are aligned on the end surfaces of the fibers 2 and 3. When the fiber 2 is rotated in parallel to the one end surface of the other fiber 3, moire fringes are formed, which can be observed at the projecting end surface of the fiber 3. Therefore, in the above-described construction, if the flywheel 10 is rotated, the moire fringes at the end surface of the fiber 3 are moved, and accordingly, by measuring the amount of the movement of the moire fringes on a screen of a television monitor 6 or automatically detecting the amount of the movement by an image processor 7, the rotating angles of the flywheel 10 can be measured in a simple arrangement with high accuracy.
01 Jan 1989
TL;DR: A moire profilometry method has been developed that is capable of inspecting objects whose size is limited only by the available laser power and which makes it usable either for human or robot adjustment of the test object or for automated pass/fail inspection.
Abstract: A moire profilometry method has been developed that is capable of inspecting objects whose size is limited only by the available laser power. The moire contours are generated in real time by projecting variable spacing gratings upon the target and filtering the image either optically, in the video signal, or in the computer. The system is designed to compare the surface shape of a test object with a previously stored image of a perfect object, and to display the surface errors superimposed on a video image of the test object. A unique feature of the system is the continuously variable depth resolution which makes it usable either for human or robot adjustment of the test object or for automated pass/fail inspection.A moire profilometry method has been developed that is capable of inspecting objects whose size is limited only by the available laser power. The moire contours are generated in real time by projecting variable spacing gratings upon the target and filtering the image either optically, in the video signal, or in the computer. The system is designed to compare the surface shape of a test object with a previously stored image of a perfect object, and to display the surface errors superimposed on a video image of the test object. A unique feature of the system is the continuously variable depth resolution which makes it usable either for human or robot adjustment of the test object or for automated pass/fail inspection.
16 Jan 1989
TL;DR: In this paper, the process of moire interferometry is given mathematical description in terms of the classical theory of optical interference, and the governing relationship between displacement and fringe order is derived.
Abstract: The process of moire interferometry is given mathematical description in terms of the classical theory of optical interference. The governing relationship between displacement and fringe order is derived, and the analysis is extended to cover carrier patterns, double exposure methods, and initial fringe pattern elimination. Various processes for obtaining patterns of displacement derivatives are also described mathematically.