Showing papers on "Moiré pattern published in 1982"
TL;DR: In this paper, a fast Fourier transform method of topography and interferometry is proposed to discriminate between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour generation techniques.
Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.
3,650 citations
TL;DR: The article resumes the theory in a unifying approach and presents a comprehensive list of applications ofOptical methods of shadow and projection moire for mapping the absolute shape of a given surface or the difference between that surface and a master one or its accidental shape change.
Abstract: Optical methods of shadow and projection moire are particularly suitable for mapping the absolute shape of a given surface or the difference between that surface and a master one or its accidental shape change. Essentially, product moire fringes are obtained on an image plane where a "filter" grating analyzes the image of the test surface which has been "coded" by projecting a master grating on it. The article resumes the theory in a unifying approach and presents a comprehensive list of applications.
135 citations
TL;DR: In this article, a review of the progress in high-sensitivity moire interferometry is presented, with a comparison of the theoretical limit of X/2 displacement per fringe in one demonstration.
Abstract: Recent progress in high-sensitivity moire interferometry is reviewed. Interference patterns reveal full-field contour maps of in-plane displacements. Sensitivity corresponds to moire with 1200 lines/mm (30,480 //in.) for most examples, but approaches the theoretical limit of X/2 displacement per fringe in one demonstration. Techniques for producing cross-line phase gratings on specimens are described, as well as use of real and virtual reference gratings. Carrier patterns and optical filtering are used to cancel initial or no-load patterns. Diverse applications are illustrated.
101 citations
TL;DR: A computer-aided system for reconstruction of the surface of an object from optically generated interferometric fringes is described conceptually, and the parts of the system are demonstrated.
Abstract: A computer-aided system for reconstruction of the surface of an object from optically generated interferometric fringes is described conceptually, and the parts of the system are demonstrated. Fringe patterns of macroscopic objects were produced with moire contouring, while a reflection interference microscope was used to examine minute surface features. Three-dimensional shaded images of the surface were generated using techniques of image processing and computer graphics. An algorithm for obtaining wire frame surface representations from TV images of fringes is described, and the limitations of the proposed system are discussed.
55 citations
TL;DR: In this paper, a modification of the optical setup is proposed to change the observed fringe patterns by modifying the optical configuration of the holographic interferometry system, and well-known procedures of the moire method can be applied to holographic Interferometry.
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.
50 citations
TL;DR: Moire fringe maps represent in detail the three-dimensional displacements that have occurred in engineering structures measured by applying a fine grid pattern to the surface and photographing this in white light with a specially modified 35 mm camera.
Abstract: Deformations of engineering structures are measured by applying a fine grid pattern to the surface and photographing this in white light with a specially modified 35 mm camera. The processed negatives are analyzed in a spatial filtering system to produce moire fringe maps which represent in detail the three-dimensional displacements that have occurred. Measurements have been obtained from brick built and concrete structures, from steel surfaces heated to 600°C, and from plastic and composite materials.
44 citations
TL;DR: In this article, a general purpose fringe pattern processing facility was developed in order to analyze moire photographs used for scoliosis diagnoses and interferometric patterns in optical shops, where a TV camera reads a fringe profile to be analyzed, and peaks of the fringe are detected by a microcomputer.
Abstract: A general purpose fringe pattern processing facility was developed in order to analyze moire photographs used for scoliosis diagnoses and interferometric patterns in optical shops. A TV camera reads a fringe profile to be analyzed, and peaks of the fringe are detected by a microcomputer. Fringe peak correction and fringe order determination are performed with the man-machine interactive software developed. A light pen facility and an image digitizer are employed for interaction. In the case of two-dimensional fringe analysis, we analyze independently analysis lines parallel to each other and a reference line perpendicular to the parallel analysis lines. Fringe orders of parallel analysis lines are uniquely determined by using the fringe order of the reference line. Some results of analysis of moire contourograms, interferometric testing of silicon wafers, and holographic measurement of thermal deformation are presented.
36 citations
TL;DR: In this article, a family of optical methods are developed for the measurement of slope and curvature of flexed plate surfaces using gratings as filters in the light path emerging from the flexed surface.
Abstract: A family of optical methods are developed for the measurement of slope and curvature of flexed plate surfaces. Slope and curvature contour fringes are generated by using gratings as filters in the light path emerging from the flexed surface. General field equations are derived for gratings placed anywhere in the field. Depending upon the pitch and the position and the number of gratings used, a variety of techniques are obtained for the contouring of slopes or curvatures. When a low density grating is used, the resulting shadowgram yields slope contour fringes if it is placed at the real focal plane of the field lens. Otherwise, the shadow gram fringes are not slope contours. However, slope contours can be obtained if a double-exposure technique or a double grating is used to generate the moire fringes. If a grating of sufficiently high frequency is used, the resulting pattern is a curvature pattern, for which a monochromatic light source is needed. A successive plotting method is also proposed for curvature contouring whereby white light and a grating of arbi-trary pitch can be used. The methods are verified by a series of experiments using cantilever beams and clamped circular plates. Applications to a variety of other problems, including flexure wave propagation, are also demonstrated.
28 citations
TL;DR: Three techniques for digital smoothing of fringe patterns when the intensity of such a pattern is digitised and fed into a computer are discussed here.
24 citations
TL;DR: Two digital systems are developed for the automatic measurement of 3-D shapes using moire techniques—an automatic3-D shape measuring system using the scanning moire method and an interactive fringe analysing system for moire fringe photographs.
21 citations
IBM1
TL;DR: In this paper, a Fourier transform analysis of the moire-pattern formation commonly observed in images reconstructed from scanned halftone pictures is presented, taking into account the scan frequency, the scanner sampling frequency, and the nonzero size of the scanner aperture.
Abstract: We present a Fourier-transform analysis of the moire-pattern formation commonly observed in images reconstructed from scanned halftone pictures. The analysis takes into account the halftone screen frequency, the scanner sampling frequency, the nonzero size of the scanner aperture, the angle between the scan direction and the halftone screen and the shape (square or parallelogram) of the scanner sampling lattice. A fortran program based on the mathematical analysis is shown to permit not only simulation of a wide variety of moire phenomena actually observed in practice but also explanation of their origin. Several important observations are discussed, including the following: (1) Moire fringes can result from the beating together of clusters of Fourier spatial frequencies. (2) Moire patterns other than square-grid fringe arrays are associated with parallelogram (nonsquare) sampling lattices. (3) Fixed-value thresholding intensifies moire patterns.
TL;DR: In this article, the rays that form moire fringes in projection type moire topography are discussed and an alternative formula based on principal rays is proposed and compared with the conventional nodal ray formula.
TL;DR: Determination by means of the time-averaged shadow moire method of the vibrating phase of an arbitrary position on the object is presented, where the illumination angle of the reference grating is periodically oscillated at the same frequency as the object vibration.
Abstract: By the general time-averaged shadow moire method only amplitude distribution of an object vibration is recorded. In this paper determination by means of the time-averaged shadow moire method of the vibrating phase of an arbitrary position on the object is presented. In this method the illumination angle of the reference grating is periodically oscillated at the same frequency as the object vibration. Therefore, stationary contour fringes are shifted to a vibrating region that vibrates in-phase oscillation of the illumination angle. Accordingly it is possible to determine the vibration phase of each region on the object as the signal phase added to the illumination angle oscillator.
TL;DR: In this paper, the shape of an object is determined by contouring holography and the displacements are determined by holographic-moire in the form of contour-line maps for the displacement components inx, y andz direction.
Abstract: A procedure is described to determine the surface strains of objects of arbitrary shape using the same setup. The shape of the object is determined by contouring holography. The displacements are determined by holographic-moire in the form of contour-line maps for the displacement components inx, y andz direction. From these maps, the so called basic strains' are derived as if the object were flat. Formulas are given to transform these basic strains' into surface strains.
TL;DR: It is shown that, when a certain space exists between a linear rectangular grating and a lenticular grating, the resulting moiré pattern is alinear rectangular grid.
Abstract: It is shown that, when a certain space exists between a linear rectangular grating and a lenticular grating, the resulting moire pattern is a linear rectangular grid. An analysis of the phenomenon is provided, and some of its applications to moire analysis are demonstrated.
01 Nov 1982
TL;DR: In this article, the authors developed two types of interactive fringe pattern analysis systems: RIFRAN I in which image processing technique is applied and sectional shape type model is built up semi-automatically.
Abstract: Fringe pattern such as interference fringe or moire fringe have been used widely to measure a surface shape, deformation, displacement and so on without contact. However, quantitative analysis of fringe pattern is not always so easy. In this paper, the authors developed two types of interactive fringe pattern analysis systems. One of them is called RIFRAN I in which image processing technique is applied and sectional shape type model is build up semi-automatically. Another one is called RIFRAN II in which tablet digitizer is provided for input of fringe positions and contour line type model is constructed. Furthermore, 3-D model processing systems are developed for proceeding analysis. Key Words: Fringe pattern, Interactive input, 3-D shape model, Sectional shape, Contour line, Quantitative analysis© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this paper, the authors investigated the intensity distributions in electron micrographs by means of theoretical calculations and an experimental study of composition-modulated GaAsP crystals for the case when the diffraction vector is varied in moving both, in the image plane and along the scattering column.
Abstract: Intensity distributions in electron micrographs are investigated by means of theoretical calculations and an experimental study of composition-modulated GaAsP crystals for the case when the diffraction vector is varied in moving both, in the image plane and along the scattering column It is shown that contrast in this case may be regarded as a superposition of the moire fringes and the displacement contrast Specific features of the images are analyzed for the laws of a) stepwise, b) sinusoidal, and c) continuous variation of composition
[Russian Text Ignore]
TL;DR: In this paper, a theory based on the geometric shadow of light can account for the spatial location of moire fringes in topographical applications, where the fringe location depends on the optical arrangement of the system and also on the surface slope of the specimen.
TL;DR: In this paper, an analytical method of predicting the intensity profile of the moire fringes formed by a three-dimensional grating is proposed, which is proved to be effective in determining the appropriate structure of the grating and the experimental conditions for directional moire topography.
Patent•
11 Jun 1982
TL;DR: In this paper, the authors proposed a method to prevent a moire from occurring at the time of halftone picture image part scanning by comparing a specified detection signal with a picture signal to discriminate whether they coincide with each other or not.
Abstract: PURPOSE:To prevent a moire from occurring at the time of halftone picture image part scanning in a halftone picture image detector for a scanning paper used for a facsimile terminal equipment, by comparing a specified detection signal with a picture signal to dicriminate whether they coincide with each other or not. CONSTITUTION:The output of a shift register 2 holding a detection signal, which is composed of code strings where (n) pairs of blacks and whites in which one black and one white make one pair line up in a halftone cycle T corresponding to the position of the black dot and white dot in the halftone, and the output of a shift register 1 where a picture signal is inputted for every picture element are compared in an exclusive OR gate 3 to discriminate whether or not the picture signal coincides with the line of 1 and 0 of the detection signal. If they agree each other, a halftone detection signal is outputted from an AND gate 4, and a halftone picture image part and non-halftone picture image part can be separately detected.
TL;DR: In this article, the aperture filtering of lenses for the purpose of moire topography is described, where the circular iris of a lens is replaced with a rectangular one whose long side is parallel with the bars of the grating, and both visibility of the fringes and the exposure condition are greatly enhanced.
TL;DR: In this paper, an optical bench set up used to increase the sensitivity in moire analysis of strain is described, which consists of a laser light source, spatial filter, collimating lens, loading frame, Fourier transform lens, imaging lens with mask, and the image recording system.
Abstract: An optical bench set up used to increase the sensitivity in moire analysis of strain is described in this paper. The optical system employed for this purpose consists of a laser light source, spatial filter, collimating lens, loading frame, Fourier transform lens, imaging lens with mask, and the image recording system. Models up to a maximum size of 200 mm diameter can be handled using the set-up developed. This paper describes in detail all the physical components of the system set up in the experimental stress analysis laboratory of the ‘Structural Engineering Research Centre, Madras. To illustrate the use of the set-up, moire fringes of displacement and its derivatives obtained in the case of a circular ring under diametral compression have been presented here.
01 Jan 1982
TL;DR: In this paper, the authors reported a promising automatic 3D shape measuring method, called the scanning moire method, which automatically eliminates the shape ambiguity problem, which is serious in the conventional moire topography.
Abstract: The ease of measuring diffuse surfaces has been significantly increased by the development of moire topographic techniques [1]. Recently, we reported a promising automatic 3-D shape measuring method, called the scanning moire method [2]. In this method, moire fringes are generated by the electronic scanning and sampling of a deformed shadow grating, instead of superposition of a reference grating in the conventional moire topography. The electronic scanning and sampling technique automatically eliminates the shape ambiguity problem, which is serious in the conventional moire topography. A practical measuring system has been developed [3], especially for medical applications. An optical system of a moire camera for medical application is used, and data from the photodiode array are processed by a microcomputer.
TL;DR: The overlapping of two periodic line patterns of the same general magnitude can produce larger scale visible patterns called moire fringes, although a broader examination of moire in color television would include other spurious patterns in the reproduced picture.
Abstract: The overlapping of two periodic line patterns of the same general magnitude can produce larger scale visible patterns called moire fringes. In shadow mask picture tubes a design objective is to prevent such unsought patterns from being produced by the interaction of the scan line pattern with the pattern of mask holes or phosphor dots. This goal is the subject of this paper, although a broader examination of moire in color television would include other spurious patterns in the reproduced picture. These could be caused by interference between two or more patterns such as the original subject, the target grid of the image orthicon, scan line pattern, mask-screen pattern, and carrier color signal periodicity.
TL;DR: In this article, a modified moire topographic technique has been developed to measure the surface shape of precise mechanical metal parts smoothly finished with shaving or grinding, and the difference of 3D shape of curved surfaces from a standard surface can be measured with a fringe sensitivity of several microns.
TL;DR: The technique can enable precise measurements to be made, over a limited range, of the spatial frequencies of fringe systems, projected images, or grids, with an accuracy of 1%.
Abstract: Difficulties are often encountered in measuring the spacing of indistinct fringes such as those generated in speckle photography. Accuracies of 5% are currently typical. By forming a moire pattern between the fringes and a rotatable reference grid, one can use angular measurements instead of linear measurements, with an accuracy of 1%. The technique can enable precise measurements to be made, over a limited range, of the spatial frequencies of fringe systems, projected images, or grids.