Showing papers on "Moiré pattern published in 1988"

Application Of Moire Analysis Of Strain Using Fourier Transform

Abstract: By shifting the discrete Fourier spectrum of the image of a deformed grating, we obtain the "complex moire pattern," from which strain distribution is given as the derivatives of the phases of the complex moire fringes. The analysis is completely automated by digital image processing. All of the laborious and subjective procedures required in the conventional analysis such as fringe sign determination, fringe ordering, and fringe interpolation are thus eliminated, permitting objective, fast, and accurate analysis. Some applications for rubber plates are shown.

Methods and apparatus for eliminating Moire' interference using quasiperiodic patterns

Abstract: Improved methods for reproducing an image are disclosed. Images are created using dots or patterns which are substantially quasiperiodic and thereby eliminate Moire interference patterns. In multi-color applications, the disclosed methods simplify the color overlay process. Also disclosed are patterns for creating half-tone images which do not exhibit Moire interference patterns when overlaid. Electronic display apparatus using these patterns are also disclosed.

Image processing apparatus using inclined line screens to reduce Moire

Abstract: There is disclosed an apparatus for processing a halftone image into a digital dot image. There are generated plural dots for the data of each pixel so as to form line screens in such a manner that smallest ones of the dots among the pixels constitute a line screen while other dots constitute line screens inclined to the scanning direction, in order to reduce Moire fringe pattern.

Moiré method and zone plate pattern inaccuracies

Abstract: Moire patterns obtained from superimposed zone plates with common types of pattern inaccuracies are analyzed. Tolerances for the distortions characterized as ellipticity, radial displacement, and nonconcentricity of the zones, are obtained from the corresponding equations for lenses. The formulas for moire fringes resulting from superimposed zone plate patterns having these defects are derived. The feasibility of moire pattern techniques to detect and measure inaccuracies of the zone plate is demonstrated. The sensitivity and the limitations of the method are discussed.

Method for coding facsimiles

Abstract: A method for coding facsimiles which are acquired when scanning originals containing halftone areas. In order to eliminate moire and/or for the purpose of a data compression, a coding of the halftone areas corresponding to an unsharper imaging in comparison to the original is executed such that the so-called halftone raster is suppressed. The method provides that a detail area is defined with a respective halftone area and is coded with a "detail code". At least a remaining area of the halftone area is coded with an "unsharp code". The method offers the advantage of the possibility of an improved detail reproduction given simultaneous suppression of a moire and given a good data compression.

Moire analysis of strain by Fourier transform.

Abstract: By shifting the discrete Fourier spectrum of the image of a deformed grating, we can obtain "the complex moire pattern". Strain distribution is given as the derivative of the argument of the complex moire pattern. The analysis is completely automatized by introducing the digital image processing. All of the laborious and subjective procedures reguired in conventional analysis such as fringe sign determination, fringe ordering, and fringe interpolation are completely eliminated and objective, fast and accurate analysis can be made.

Method and device for observing moiré patterns of surfaces under investigation in conjunction with the application of the projection moiré method with phase shifts

Abstract: Dynamic and brief measurement of surfaces and surface variations by means of the projection moire method in combination with phase shifts. The invention relates to the recording of surfaces and their deformation in the direction of observation. It relates to a method with exemplary embodiments of the device for the simultaneous pulling- in of the individual images which are required for the application of the phase shift method when the latter is used in the case of the projection moire method. The brief observation and recording of moving surfaces is rendered possible by the advance from serial to parallel pulling-in of the shifted patterns. The temporal resolution is now a function only of the storage/exposure of a photograph.

Generation of moiré by nonlinear transfer characteristics

Abstract: The intermodulation of signal frequencies, or moire, is an effect generally encountered in situations in which periodic or quasi-periodic structures are superimposed. Most familiar are the striking low-frequency patterns achieved by the multiplicative superposition of two structures. In other situations, the intermodulation of signal frequencies may be caused by nonlinear distortions of an input signal. This can be a desired feature in measuring applications or a noise source in transmission or display. Effects of nonlinear transfer characteristics on input signals consisting of more than one frequency are shown. The dependence of resulting moire frequencies on the nonlinearity is evaluated, and common nonlinearities are compared by simulating a moire topography experiment.

Exact interpretation of moiré fringe patterns in digital images

Abstract: Geometric moire enjoys the advantages of simplicity of technique and equipment, and the ability to use white light. However, resolution has been hampered by difficulties in employing more than 40 l per mm. The present paper illustrates the aspects of a digital imaging system relevant to the determination of fractional fringes, and enables reliable analysis from extremely few fringes.

Inclination moire type shape measuring method

Abstract: PURPOSE:To dispense with the adjustment of the inclination of a body to be measured, by a method wherein moire fringes are generated using a plane lattice and a spot-or slit-like beam source, and the beam source and the image forming point of an observation system are positioned at vertical distances unequal from the surface of the lattice when the surface shape of the body to be measured is calculated by utilizing the moire fringes and a beam cutting surface group is inclined with respect to the body to be measured. CONSTITUTION:A large-scaled lattice 13 is stretched across above a roller 21 feeding a steel plate 22 in the manner so provide an interval and the beam from a laser beam source 17 such as YAG is allowed to be incident to a reflecting mirror 19 through a beam expander 18. Next, the reflected beam from the mirror 19 is projected on the lattice 13 using a concave lens 20 but, at this time, the lens 20 is inclined with respect to the lattice 13. By this method, the photograph of the moire fringes generated on the surface of the steel plate is taken by an ITV camera 23 and the moire fringes are observed by a monitor television 24 and inputted to an image processor 25 to be displayed on an output display device 26. Thereafter, the depth of the fringes generated in the fringe image, the fringe interval to a reference surface and flatness are used to operate a shape.

Automatic analysis of moiré fringe patterns by using an image-processing system

Abstract: This paper presents the whole process of analyzing moire fringe patterns by using a computer-image-processing system. The main steps include: recording a fringe pattern, eliminating noise, thinning the fringes, assigning the fringes with fringe-order information, computing the strain field, outputing data tables, data curves, color two-dimensional computational displays and outputing in relief three-dimensional displays which represent strain and displacement. The method is highly automatic and gives visualized pictures and accurate results.

New Apparatus of Moiré Iso-hypsigraphy by Parallel Light Projection and Parallel Reflecting Light Recording

Abstract: A new apparatus of moire iso-hypsigraphy was designed and produced to examine relatively small materials such as human skulls, innominate bones and scapulae. The parallel light source method producing moire fringes was adopted, which is much appropriate for the small objects. The reflected light, furthermore, was considered, because moire fringes produced by the parallel light needed to be recorded by the camera system in condition of nearly parallel reflected light. For recording system a 35mm camera with a 800mm focal length lens was selected. In this system one can measure the photographs with moire fringes under the permissible error, i. e. 1%. Moire producing parts of an apparatus has many improvements for the small objects: condenser lens, field lens, reflecting mirror and threads in grating. In the apparatus the skull fixer and co-ordinates indicator, in particular, were specially designed. By them the skulls on which the moire fringes are produced can be fixed in the Frankfort horizontal plane. In the photographs of them the moire fringes on the skull will indicate coronal sections as exact equal contours.

Optical linear scale

Abstract: PURPOSE:To take an accurate measurement by providing an optical sensor and a scale plate and finding the relative position and movement quantity of a body to the extent of the side of one unit of a photodetecting element, and further interpolating a finer movement quantity than the measurement resolution of the photodetecting element by using moire fringes. CONSTITUTION:The optical sensor 1 where many photodetecting elements 2 are arranged in two arrays and a light source 7 are fixed in one body and move relatively in parallel to the array direction of slits 4 (414n44) on the scale plate 3. Here, when the presence of fringe patterns 4 and 5 is ignored, illumination light emitted by the light source 7 is transmitted through slits 4 of the scale plate 3 to project the image of the slits 4 on the sensor 1. Then, outputs from respective elements 2 of the sensor 1 are inputted to an arithmetic circuit. In this case, the shape and intervals of the slits 4 are selected and the position or movement quantity of the scale plate 3 is detected. Displacement smaller than one picture element of the elements 2, however, can not be detected by this, so moire fringes are formed by fringe patterns 5 and 6 provided to the surfaces of the sensor 1 and scale plate 3 for interpolation, and the moire fringes are read.

Moire topographic camera

Abstract: PURPOSE:To obtain a contour line even in an object having a small dimension of about 5mm, by splitting laser beam into two beams and allowing the plane constituted of the center axes of said beams to cross the scanning line direction of an image pickup device at a right angle. CONSTITUTION:This topographic camera is constituted of an expansion lens 204 expanding laser beam, a beam splitter 205 splitting laser beam into two beams and a reflecting mirror 206 projecting said beams to an object at a predetermined angle theta3. Then, two split laser beams are allowed to cross each other at the angle theta3 to irradiate the object and the Young's interference fringe generated by this is utilized as an equal interval linear lattice becoming a reference lattice and the fringe pattern appearing on the surface of the object by said fringe is formed into an image on the image pickup surface of an image pickup device 209 along with the image of the object. The moire line generated by the interference of the fringe pattern of the object formed into the image and the TV scanning line of the device 209 is obtained as a contour line. Therefore, it becomes unnecessary to form the reference lattice into an image on the object by a lattice projection lens and the clear contour line is obtained even in the object having a small dimension of about 5mm capable of projecting a minute interval fringe to the object.

Automatic Measurements Of The Small Angle Variation Using A Holographic Moire Interferometry And A Computer Processing

Abstract: A method for automatic measurement of the small tilt angle variation of an object surface by using a digital holographic moire interferometryI based on computer processing is described. The test surface is placed in the middle of a set of two gratings. A monochromatic plane wave illuminates the first grating and undergoes diffraction. After being reflected by the test surface, the first grating produces the magnified Talbot image. The moire fringe is generated by superimposing this Talbot image on the second grating. The inclination angle of the moire fringe is a measure of the tilt angle of the test surface. Fast and automatic measurement has been achieved with improved accuracy and sensitivity. In the experiment, the small tilt angle variation of the plane mirror is measured.

On the measurement of finite strain by the Moire method.

Abstract: A formula of finite strain expressed in terms of each distance between Moire fringes is newly deduced which is useful for the analysis of in-plane large deformation. This formula allows us to draw the two-dimensional distributions of Euler-Almansi strain on the flat surface from the measurement of the distances between Moire fringes on the initial and deformed material. The strains thus measured are inevitably total ones (not incremental). A few examples of finite strain distributions measured by this method are demonstrated with respect to flat specimens deformed under uniaxial tension beyond the onset of diffuse-necking.

Generation Of Moire Contours With Acousto-Optic Cells

Abstract: Moire contours are seen on a curved surface viewed through a grating when the surface is illumnated with a matched grating. We have been able to replace both the projection and viewing physical gratings with gratings of variable spacing generated in acousto-optic cells, and have been able to observe and record Moire contours. The gratings are generated by amplitude modulating 70 MHz AO cells with a 1 to 10 MHz square wave. The gratings become visible on the curved object by strobing the illuminating laser beam with 50 nsec pulses by means of an AO modulator. Data is given showing the variation in grating spacing with AO modulation frequency. Figures are presented showing the variation of the Moire contour spacing with the AO modulation frequency and with target contour. The results for an angled flat plate target are compared to those in the literature.

Use of the Double-illumination Method with Two Light Sources in Moiré Topography

Abstract: Generalizations of the double-illumination method by two light sources in moire topography are discussed in terms of the three-dimensional analysis of its mathematical basis developed for the following two cases: (a) where, the grating has a light-intensity distribution expressed by a fundamental harmonic wave, and (b) where it has a light-intensity distribution expressed by an arbitrary periodic function with many components. The characteristics of the two cases were studied in comparison with several examples of the moire patterns observed by the double-illumination method. From the results, it can be concluded that the transmittance of the grating is of the fundamental sine-wave type in the case of the solid-grating type and that the two-source method is significant for obtaining shadow-free moire patterns from complex surfaces of an object such as a skirt.

The Visibility Of Moire' Patterns

Abstract: Unacceptable Moire' distortion may result when images that include periodic structures such as halftone dots are scanned. In the frequency domain, Moire' patterns are the result of visible aliased frequencies. In the spatial domain, the aliased frequency components correspond to cyclic changes in the size of halftone dots which are visible as periodic "beat" patterns. Moire' formation depends on the following factors: (1) halftone screen frequency, (2) scan frequency, (3) 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) ink flow on paper during printing. This paper analyzes the visibility of Moire' patterns in terms of these factors. Moreover, the paper describes an approach to reduce the visibility of Moire' patterns by manipulating the Moire' formation factors directly rather than by post-scan processing. Computer simulated, and actual scan images are presented to illustrate the approach.

A shearing-holographic-moire for strain patterns

Abstract: A new holographic-moire is presented. The object is illuminated by double beams separately so that two different carriers are introduced. Pure strain patterns are obtained by filtering twice and shearing the plate.