Showing papers on "Moiré pattern published in 1998"

Optical Methods of Engineering Analysis

Abstract: Introduction 1. Light and interference 2. Classical interferometry 3. Photoelasticity theory 4. Basic applied photoelasticity 5. Photoelasticity methods and applications 6. Geometrical moire theory 7. In-plane motion and strain measurement 8. Moire mapping of slope, contour and displacement 9. Diffraction and Fourier optics 10. Moire with diffraction and Fourier optical processing 11. Procedures of moire analysis with optical processing 12. Principles of moire interferometry 13. A moire interferometer 14. Experimental methods in moire interferometry 15. Holographic interferometry theory 16. Holographic interferometry methods 17. Laser speckle and combinations of speckle fields 18. Speckle photography 19. Speckle correlation interferometry 20. Electronic speckle pattern interferometry 21. Phase shifting to improve interferometry.

Holographic moire, an optical tool for the determination of displacements,strains, contours, and slopes of surfaces

Abstract: In conventional holographic interferometry, the observed fringe patterns are determined by the object displacement and deformation, and by the illumination and observation configurations. The obtained information may not be in the most convenient form for further data processing. To overcome this problem, and to create new possibilities, holographic fringe patterns can be changed by modifying the optical setup. As a result of these modifications, well-known procedures of the moire method can be applied to holographic interferometry. Components of displacement and components of the strain tensor can be isolated and measured separately. Surface contours and slopes can also be determined.

Comparative holographic moire interferometry in real time

Abstract: A holographic moire technique is developed which allows one to compare the resistance to strength in real time of two nominally identical specimens. The moire interference pattern gives contours of path variations related to the difference in displacements of the two specimens. The method is whole field and noncontacting; it is demonstrated by comparing deflections of two square plates clamped along the edges and subjected to centrally concentrated loads.

Measurement of transient deformations with dual-pulse addition electronic speckle-pattern interferometry

Abstract: We describe an electronic speckle-pattern interferometry system for analyzing addition fringes generated by the transient deformation of a test object. The system is based on a frequency-doubled twin Nd:YAG laser emitting dual pulses at a TV camera field rate (50 Hz). The main advance has been the automatic, quantitative analysis of dual-pulse addition electronic speckle-pattern interferometry data by the introduction of carrier fringes and the application of Fourier methods. The carrier fringes are introduced between dual pulses by a rotating mirror that tilts the reference beam. The resulting deformation-modulated addition fringes are enhanced with a deviation filter, giving fringe visibility close to that of subtraction fringes. The phase distribution is evaluated with a Fourier-transform method with bandpass filtering. From the wrapped phase distribution, a continuous phase map is reconstructed with an iterative weighted least-squares unwrapper. Preliminary results for a thin plate excited by an acoustic shock show the suitability of the system for the quantitative evaluation of transient deformation fields.

Improved phase-shifting method for automatic processing of moiré deflectograms

Abstract: An improved moire deflectometry phase-shifting technique is presented. A squared grating is used to multiplex the information of the deflections in two orthogonal directions in one image. This procedure avoids the need to rotate the gratings to obtain complete deflection information. However, the use of these gratings makes impossible the application of standard phase-shifting algorithms. Specifically, the problems associated with the nonsinusoidal profile of the moire fringes and the low-modulation areas produced by the square gratings are solved. A modified moire deflectometry phase-shifting method is designed to deal with these problems. In addition, a method to obtain the zero order of the prismatic effect is developed. The technique configures a complete and automatic method of mapping ray deflections. From them the refractive power maps can be derived. Experimental results obtained with a progressive-addition lens are shown.

Moiré security device

Abstract: A security document or device having a first array of dots or lines having a predetermined number of lines per centimetre and a predetermined screen angle, a second array of dots or lines applied to or produced by a separate device and producing a grey scale visible effect, said second array being capable of being superimposed over the first array and having a different number of lines and screen angle calculated from the number lines and screen angle of the first array to produce a visible moire pattern when the arrays are superimposed to establish the authenticity of the document or device.

Method of an apparatus for correcting halftone-dot image data and method of correcting halftone-dot threshhold data

Abstract: Halftone-dot image data (H) in a position space is converted into data (S1) in a frequency space by fast Fourier transform unit (40), and data (S2) including low-frequency noise components whose frequency is lower than the fundamental frequency component of halftone dots is extracted from the data in the frequency space by a low-pass filter (42). The extracted data including the frequency noise components is inversely converted into image data (N) in the position space by an inverse fast Fourier transform unit (44). Pixels of the halftone-dot image data (H) in positions which correspond to pixels including the noise components in the inversely converted image data (N) are corrected by a corrector (46) such that the noise components will be reduced. The correcting process is in the position space, and can simply be carried out. A binary halftone-dot image generated from the corrected halftone-dot image data (Ha) is substantially free of any moire pattern which would otherwise be caused by an interference between the output resolution of an image output device and the frequency of halftone dots.

System providing hybrid halftone

Abstract: A system provides a halftone image having reduced moire patterns by applying a screen function of the type having a first function exhibiting symmetry about a point and a second function exhibiting symmetry about a line. In a progression of tone levels, such a screen function creates first dots, then lines, then dots. For example, a screen function may include the sum of a first function of the type (1−cos(pi*(x+y))*cos(pi*(y−x))) and a second function being a piecewise linear function of x, where {x,y} is a coordinate location in a unit cell mapped to a halftone cell mapped to the image pixel grid. In other embodiments, a unit cell is defined on the grid by a vector. The vector has a component along an axis of the grid. The component has a noninteger length. Unit cells of the type so defined implement rational tangent angles not possible with conventional halftone cells.

Comparative holographic moire interferometry for nondestructive testing : comparison with conventional holographic interferometry

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.

System for taking displacement measurements having photosensors with imaged pattern arrangement

Abstract: The present invention is generally directed to a system for taking displacement measurements of an object. The invention utilizes the Moire effect to take precise displacement measurements of an object. In this regard, a visible pattern is disposed on an object, and a plurality of photosensors are uniformly spaced apart from the visible pattern. Importantly, the spacing between the photosensors is slightly different than the spacing between light and dark lines forming a projection or image of the visible pattern. This allows the invention to utilize the Moire effect to accurately compute precise displacements or movements of the object. In this respect, electrical signal generated by the photosensor array will embody a repeating envelope pattern resulting from the difference in the pitch of the photosensors and the pitch of the projection or image of the visible pattern. This envelope has a spatial frequency that is significantly lower than the fundamental repetition frequency of either the image (or projection) of the visible pattern or the photosensor array, where these frequencies of the image or projection of the visible pattern and the photosensor array are equal to the reciprocal of the distances separating adjacent repetitions of pattern within the image of the visible pattern or the reciprocol of the pitch of adjacent photosensor elements respectively. Thus, small lateral motion of the object bearing the visible pattern, made parallel to the direction of the repetition of the repeating patterns, produces a relatively large shift in the position of the signal envelope which has a lower spatial frequency.

Two-frequency Phase-Shifting Projection Moire Topography

Abstract: Adopting phase-shifting technique in moire topography provides many advantages in measuring complex surface profiles with varying reflectance. However, still the so- called 2(pi) -ambiguity problem remains, which limits the maximum measurable step height difference between two neighboring sample points to be less than half the equivalent wavelength of moire fringes. To cope with the problem in this investigation, a two-wavelength scheme of projection moire topography is proposed along with necessary hardware design considerations. Test results prove that the proposed scheme is capable of finding absolute fringe orders automatically, so that the 2(pi) -ambiguity problem can be effectively overcome so as to treat large step discontinuities in measured surfaces.

Minute displacement-measuring apparatus using moire fringe

Abstract: PROBLEM TO BE SOLVED: To provide a minute displacement-measuring apparatus utilizing moire fringes which can quickly measure a displacement in an optional direction within a plane perpendicular to the direction of a collimation line of an object to be observed, in a non-contact manner with the use of moire fringes. SOLUTION: A checkered solid grating 1 is photographed by a TV camera 3. A photographed output is converted to a digital signal by an A/D converter 41 included in an image-processing circuit 4. Image data of the solid grating are stored in a memory 42. Image data of a reference grating formed separately and the stored image data of the solid grating are added and averaged by an operation circuit 43, whereby image data of moire fringes are output. A minute shift of an observation point is measured on the basis of a shift of the image data.

X-ray angle interferometry: a practical set-up for calibration in the microrad range with nanorad resolution

Abstract: X-ray interferometry is a crystallographic diffraction technique utilizing a moire effect generated by the lattice. If almost perfect silicon single crystals are employed, scanning of the periodic moire can be used for the calibration of translation or rotation on a nanometric scale since the lattice parameter is well known in terms of the SI unit of length. A monolithic x-ray angle interferometer consisting of two crystal blocks and a connecting flexure spring allowing relative rotation was manufactured. Each block supports two x-ray optical lamellae. Their optimum thickness for good visibility of the angular moire fringes during rotation was calculated using the dynamical theory of x-ray diffraction. The main block serves as the base of the interferometer and also incorporates the piezoelectric drive. This arrangement of three bimorph actuator blades allows angular scanning through the zero degree position in order to use the full Bragg reflection width. Pre-tensioning of the flexure spring, balancing of the rotating part and angular scanning are possible simultaneously. Different operating modes, free-running and locked to the fringe slope, were tested. This very compact device can be used as a stand-alone instrument or as a fine scale in a large angle measuring calibrating facility.

Method and apparatus for providing moire effect correction based on displayed image resolution

Abstract: In a display monitor, a horizontal synchronization signal having a horizontal scanning frequency is received by a first circuit. A vertical synchronization signal having a vertical scanning frequency is received by a second circuit. A moire correction signal that is proportional to a horizontal resolution of the displayed image is generated by dividing the horizontal scanning frequency by the vertical scanning frequency.

Multiplicative moiré two-beam phase-stepping and fourier-transform methods for the evaluation of multiple-beam fizeau patterns: a comparison.

Abstract: A phase-evaluation method of multiple-beam Fizeau patterns that combines two-beam phase-stepping algorithms with the moire effect was previously reported [Appl. Opt.34, 3639–3643 (1995)]. The method is based on a multiplicative moire image-formation process obtained by the direct superposition of high-frequency multiple-beam Fizeau carrier fringes upon a transmission grating (working as a phase modulator). We present a comparison between this multiplicative moire two-beam phase-stepping method and the well-known Fourier-transform method for the topographic measurement of an undoped silicon wafer. The discrepancy between the two methods yields a rms phase-difference value of the order of (∼2π/90).

Hybrid wedge plate-grating interferometer for collimation testing

Abstract: A new type of collimation testing technique using a single wedge plate in conjunction with a dual-field grating has been described. Interference pattern produced by a wedge plate illuminated by the test beam is superposed on a grating to get moire fringes. By using two different types of dual-field gratings, two testing configurations are obtained. These dual-field moire patterns provide self-referencing and improved sensitivity in collimation testing. The principle of the proposed techniques and experimental results are presented.

Intensity modulated moire and its intensity-phase analysis

Abstract: Moire topography has the advantage that it just requires a single image, but it cannot discern the fringe order. So, it is difficult to discern the connection among fringes in the case where the fringe orders are not continuous. In our work, an intensity modulated moire is presented. By modulating the transmission of projection and observation grating, the moire pattern whose fringe intensity changes with its order can be produced. The fringe order can be obtained easily from its intensity, so the skeleton of fringes in every order can be extracted to discern the global 3-D shape by intensity analysis. In the same time, we can segment the moire pattern by its fringe order. In every segment, the accurate 3-D shape among the skeletons can be calculated by phase analysis.

Shape measuring instrument for three-dimensional object

Abstract: PROBLEM TO BE SOLVED: To provide a shape measuring instrument for threedimensional object which has a simple constitution and takes a safety measure. SOLUTION: A light beam emitted from a light source 1 is two-dimensionally scanned with a two-dimensional scanner 3 after collimation by means of a collimating lens 2 and forms a striped pattern on an object 5 through an f.θ lens 4. The striped pattern 5 formed on the object 5 is observed with a TV camera 10 and transferred to a picture processor 11. Standard stripped patterns corresponding to various striped patterns are inputted to the picture processor 11 and the processor 11 extracts the Moire fringe between the standard pattern corresponding to the striped pattern formed on the object 5 and the deformed stripped pattern actually formed on the surface of the object 5. The contour lines on the surface of the object 5 can be found by analyzing the Moire fringe by means of an arithmetic and control unit 9. Moreover, the three-dimensional shape of an object having a step-like shape or an arbitrary size can be measured easily by forming at least two striped patterns having different directions and pitches on the surface of the object.

Method of and apparatus for correcting halftone-dot image data

Abstract: Halftone-dot image data (H) in a position space is converted into data (S1) in a frequency space by fast Fourier transform unit (40), and data (S2) including low-frequency noise components whose frequency is lower than the fundamental frequency component of halftone dots is extracted from the data in the frequency space by a low-pass filter (42). The extracted data including the frequency noise components is inversely converted into image data (N) in the position space by an inverse fast Fourier transform unit (44). Pixels of the halftone-dot image data (H) in positions which correspond to pixels including the noise components in the inversely converted image data (N) are corrected by a corrector (46) such that the noise components will be reduced. The correcting process is in the position space, and can simply be carried out. A binary halftone-dot image generated from the corrected halftone-dot image data (Ha) is substantially free of any moire pattern which would otherwise be caused by an interference between the output resolution of an image output device and the frequency of halftone dots.

Applications of x-ray interferometer-generated Moiré patterns

Abstract: A monolithic x-ray interferometer has been developed which provides a means of producing high-quality x-ray Moire fringes with readily controlled pitch (spacing). It was designed as a calibrator of sub-microradian angular displacements and it has successfully demonstrated the feasibility of the approach. The quality of its output, when combined with the phase imaging capabilities of interferometry and the latest generation of fringe analysis algorithms, suggests additional, novel applications. This paper first reviews the principles and performance of the system as an angular calibrator and then discusses the potential of x-ray Moire patterns in the form of an x-ray microscope and as a diagnostic tool for ultra-precision metrology. Demonstration results are given mostly in the form of images of fringe fields, since the point here is the production of original data suitable for processing by existing techniques.

Method of establishing halftone dot thresholds, apparatus for generating binary data, and image film/plate-making system

Abstract: A supercell is divided into halftone dot cells each with a highlight point at center and halftone dot cells each with a shadow point at center. Thresholds 0, 1, 2, 3, . . . assigned to pixels in the halftone dot cells each with a highlight point at center and thresholds N, N-1, N-2, N-3, . . . assigned to pixels in the halftone dot cells each with a shadow point at center are alternately determined, i.e., determined in the order of 0→N→1→N-1→, . . . →3→N-3. When the density of an original image is high, the number of blackened pixels in the halftone dot cells each with a highlight point at center and the number of blank pixels in the halftone dot cells each with a shadow point at center are equalized to each other, thus preventing moire stripes from being produced which would otherwise be caused by a periodic change in the number of blackened pixels in the halftone dot cells.

Video moire topography for in-vitro studies of the eardrum

Abstract: An opto-electronic projection moire apparatus was developed for in-vitro studies of the eardrum. Moire topograms are generated by real-time video image subtraction, yielding 25 new interferograms per second. By using different reference images, both shape and deformation fringes can be obtained, without manipulating the object or the setup. Calibration measurements show a measuring precision of 5 micrometers . The setup is used to measure the shape and deformation of the eardrum. Parameters such as, for instance, the volume displacement of the pars flaccida, can be calculated from computer evaluations of the topograms.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Method for fringe enhancement in holographic interferometry for measurement of in-plane displacements

Abstract: Theoretical background along with experimental results are given for a simple method for in-plane fringe enhancement in dual-beam illumination holographic interferometry. In this method, the fringes representing in-plane displacements arise as a moirepattern between two interferograms. To distinguish the in-plane displacement, a sequence of images is recorded while the reference mirror is continuously tilted at random. The in-plane fringes arethen found as the maximum contrast of the out-of-plane fringes in the image sequence. The resulting fringe quality is close to the quality of the out-of-plane fringes.

Method of measuring surface shape

Abstract: PROBLEM TO BE SOLVED: To judge the unevenness of the surface of an object to be measured, and measure the quantity of unevenness with precision not more than the interval of moire fringes. SOLUTION: The polarized beam emitted from a laser beam source 1 is extended by a beam expander 2 and made into parallel beams by a lens 3. The parallel beams are emitted to the surface of a object to be measured 5 through a flat grid 4 to project the shadow of the flat grid 4 to the object surface. The shadow is observed by a CCD camera 8 through the original flat grid 4, a condenser 6 and a polarizer 7. A holder 9 with a moving stage for mounting the object to be measured 5 is quantitatively movable in the vertical direction to the grid surface of the flat grid 4 by a stepping motor. When the object 5 is moved in the direction leaving the grid surface and observed, the moire fringes appearing on the object surface are moved so that the unevenness can be judged, and the quantity of the unevenness can be also measured by superposing the moire fringes on each other.

Method for measuring phase distribution and phase shift electronic moire device using it

Abstract: PROBLEM TO BE SOLVED: To raise the accuracy of measurement by detecting a sample image which is obtained by making a measuring light wave interfere with a reference light wave, and generating a moire fringe image by inter-image multiplication of a sample image signal and each of plural reference images, for calculation process. SOLUTION: An interferometer 100 generates an interference fringe image with a light wave surface containing a form information of a sample surface. A 2D image detecting means 1 inputs the interference fringe image. An image inputting means 2 extracts a video signal for one screen. A computer 11 calculates based on pixel information recorded in an image memory MAX 10a and an image memory MIN 10b to adjust a level for each pixel, and prepares a reference image signal and writes it in reference image memories 3a, 3b and 3c. Multiplier devices 4a, 4b and 4c multiply the reference image signal and a sample image signal together. A moire fringe image of moire fringes, generated from the sample image signal and the reference image signal, from which a carrier component is removed, is displayed on a monitor 23.