Showing papers on "Moiré pattern published in 1995"

High Sensitivity Moiré: Experimental Analysis for Mechanics and Materials

Abstract: Moire patterns (which form when two regular patterns of comparable frequency interfere) are sensitive indicators of changes of shape as objects rotate, heat up, or are otherwise affected by external forces Applications include non-destructive testing and evaluation, and quality and process control This text explains the theory and practice of physical measurements by high-sensitivity moire - principally moire interferometry, focusing on the mechanics and micromechanics of materials and structural elements Moire interferometry is unique in providing maps of in-plane displacements from which can be derived normal and shear strains Typical moire sensitivities are on the order of 2-4 fringes per fm displacement, but sensitivities of 17 nm per fringe contour can be reached The applications discussed include: advanced composite materials, thermal stresses, electronic packaging, fracture, metallurgy, time-dependence, and strain gage calibration The methods discussed in the text can be applied for whole-field measurements on nearly solid and solid bodies

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.

Moiré free multilevel halftoning of color images

Abstract: A halftone screen is presented for use in combination with reproduction devices that are capable of rendering more than two tone levels. The screen is optimized to minimize both tone and color shift in the presence of variations in the printing process. The intermediate density levels, which are assigned to a minority of the microdots within each halftone cell, are different within adjacent halftone cells. FIG. 9

Fringe-scanning method using a general function for shadow moiré

Abstract: We describe a new high-resolution three-dimensional measurement method for shadow moire. The method is based on the principle of using shadow moire to produce moire fringes and a fringe-scanning technique. In this method, a general function, instead of an arctangent function, is used for detecting the shape of an object. One can subsequently analyze the general function using numerical analysis with a digital computer. Two systems for static and dynamic measurements are proposed.Experimental results show that measurement accuracies in static and dynamic measurement systems are obtainable to greater than 1/50 and 1/40 fringes, respectively.

A method for reducing 2-color moire in 4-color printing.

Abstract: A method of halftone printing in four colors using, for cyan, magenta and black, halftone screens that will result in screening angles of 15, 45 and 75 degrees, as is the standard process in the art, and a halftone screen for yellow that will result in screening angles of 0, +60 and -60 degrees. This combination will diminish the 2 color moire patterns that result from the interaction between the yellow and one of the other colorants. The 0 and + or - 60 degree screening angles are generated by using a screen that produces a four-centered cell having dots that are spaced to form hexagons, when the nearest neighbors of a central dot are connected by lines, as opposed to the conventional trapezoidal orientation.

Grating Interrogations: from Small to Large Strain Measurement

Abstract: Our purpose is the direct strain measurement from the interrogation of a crossed grating marked on the surface of a specimen. The observation of the object through a master grid (as in moire method) is replaced by a direct characterization of the pattern using a Fourier transform. This gives direct access to the modification of the pitches which leads to quantification of the strain without the intermediary of a fringe pattern. The comparison between the undeformed and deformed states allows the determination of the magnitude and orientation of principal strains and of the local rigid-body rotation. We describe three analysis techniques, one using the diffraction phenomenon, another utilizing a numerical spectral evaluation and third combining diffraction and phase-shifting procedure. These grid interrogations have different domains of application and a suitable choice of these analysis techniques allows a very large measurement range (10−5 to high strain according to the grating resistance).

Fizeau phase-measuring interferometry using the moiré effect.

Abstract: The automation of the fringe pattern analysis in Fizeau interferometry combining the moire effect with the phase-stepping evaluation method is presented. In this case the phase modulator is a Ronchi grid placed at the interferometer image plane yielding a moire image, and the necessary phase steps are obtained, simply translating the grid in its own plane, perpendicular to the optical axis. A detailed description of the moire image formation as an incoherent superposition is developed. Measurements were carried out in a Fizeau interferometer built by the authors, and rms repeatabilities of less than 3 deg in the phase-difference values were attained.

Angular alignment of structures using moire patterns

Abstract: This invention uses an optical imaging system input to a computer to synthesize regularly spaced reference and test line patterns replicated from binarized edges taken from the optical images of structures to be aligned. The two patterns are then combined resulting in an interference pattern in which the spacing of moire fringes indicates the amount of movement of the structures required to bring them to a predetermined alignment. All of the procedures are observable on the interference display. These moire fringe pattern are a quantitative measure of angular alignment between the reference and test images and of the edges from the structures from which they were taken. An operator programmed and controlled template automatically processes moire edge alignment measurements. An automatic template processor generates a test sequence template from the chosen areas for measurement by the operator. A template memory module having a library of test sequence templates allows the process to be run without the selection of areas to be measured by the operator. Process imaging and logic operations are utilized in generating the automatic test sequence template.

Reproduction couleur par trames irrégulières et semi-régulières

Abstract: In the printing industry, one of the most common methods for reproducing halftone images using bilevel printing devices is clustered-dot ordered dithering The images produced using this method are quite faithful to the original and are visually pleasing Nevertheless, only rational angles are attainable with clustered-dot dithering, due to the discrete nature of the grids This phenomenon can become detrimental in the case of four-color printing, when different screen angles and maybe even different screen frequencies are used for separate color planes, thus producing a so-called Moire phenomenon Another important drawback, the so-called banding or contouring effect, is related to the limited area of basic screen elements used in traditional dithering In order to deal with these problems, we have developed, within the scope of our research, several new techniques for digital halftoning: (1) pseudo-random halftone screening, (2) a new method for generating clustered-dot halftone images having a number of reproducible gray or colour levels which is independent of the screen element size (CombiScreen), (3) rotated clustered-dot dithering, based on discrete one-to-one rotation, and (4) rotated dispersed-dot dither A new method of pseudo-random halftone screening is described It starts by obtaining the quasi-random distribution of tile centers according to some well-defined spectral characteristics We then obtain the desired tesselation of the output device space by applying the Voronoi polygonization process Then, an analytic black-dot curve is calculated according to the resampled input signal level and the area of each given tile This analytic curve is scan-converted to obtain the blackened pixels In the second approach, we associate threshold values to all pixels inside every tile according to some specially tailored analytic spot function Then, the standard threshold comparison process is applied Unlike known error-diffusion techniques, the pseudo-random halftone screening technique can be applied to a high resolution printing process The characteristic screen element size can be properly chosen so as to ensure the best trade-off between the printing process constraints and the most precise printing The described halftone algorithm seems to be appropriate for high-resolution color and blackw devices (above 1000 dpi) A new method (CombiScreen) is proposed for generating clustered-dot halftone images on raster printing devices having a number of reproducible gray or colour levels which is independent of the screen element size The dither tiles generated by this method may contain several screen elements having any rational orientation and size Threshold values are distributed among the cells of the dither tile so as to produce a large range of gray values, while at the same time preserving the clustered-dot behavior of individual screen elements When rendering images at smoothly increasing intensity levels, this new method generates few contouring effects and other visible artifacts The method works equally well for quadratic, rectangular, parallelogram and hexagonally shaped screen elements Resulting dither tiles are generally either of parallelogram or of hexagonal shape Since CombiScreen enables the screen dot frequency or orientation to be chosen independently of the number of gray levels, it has proven to be specially effective when printing at resolutions between 150 to 600 dpi with ink jet printers and at resolutions between 300 and 1200 dpi with xerographic printers A new operator of discrete one-to-one rotation is described It offers means previously unknown in the art for generating rotated screens which approximate irrational angles with high-precision, producing much less disturbing interferences and artifacts than other methods Therefore, a carefully prepared dither tile incorporating screen elements with the desired period, initial orientation, and dither threshold values defining their screen dot shape growth behavior can be rotated by discrete one-to-one rotation and keep the desired screen element period, the number of cells per screen element and the threshold values associated with each screen element cell, thereby preserving the screen dot shape growth behavior of the original dither tile Several different discrete one-to-one rotation variants are described: a small angle rotation technique valid for a subset of rational rotation angles, a rigid band technique and a technique based on discrete shearing transformations The high-quality of the so rotated dither tile is due to the fact that discrete one-to-one rotation preserves the exact number of elementary cells per screen element and their exact dither threshold values The described method provides a new range of solutions for obtaining high-quality digital angled halftone screens High-quality solutions can be found for generating three digital angled halftone screens, each 30° apart from each other, as known from traditional photographic colour screening techniques Further solutions minimizing Moire effects may be obtained by halftone screens whose first order frequency component vectors sum up to zero This new method has turned out to be particularly effective when printing with color ink jet printers at resolutions between 150 and 800 dpi as well as with xerographic printers at resolutions between 300 and 1200 dpi Rotated dispersed-dot dither is based on the discrete one-to-one rotation of a Bayer dispersed-dot dither array The halftone patterns produced by the rotated dither method therefore incorporate fewer disturbing artifacts than the horizontal and vertical components present in most of Bayer's halftone patterns In grayscale wedges produced by rotated dither, texture changes at consecutive gray levels are much smoother than in error diffusion or in Bayer's dispersed-dot dither methods, thereby avoiding contouring effects Due to its semi-clustering behavior at mid-tones, rotated dispersed-dot dither exhibits an improved tone reproduction behavior on printers having a significant dot gain, while maintaining the high detail rendition capabilities of dispersed-dot halftoning algorithms This technique has successfully been applied to in-phase color reproduction on ink-jet printers as well as to black and white reproduction on laser printers

Precision position control systems using moire signals

Abstract: A positioning accuracy of a nanometer has been obtained by a precise positioning system using moire technique. Two precise position control techniques using moire signals have been investigated. One is a differential moire technique using two grating pairs in which the control signal is the differential signal between two moire signals. The other is a technique using one grating pair. The system using the latter technique is simpler in construction. However, in the former technique, since in-phase noises in the moire signals are cancelled and the effect of the drift of the laser intensity on the positioning accuracy is small, higher positioning accuracy is obtained than in the latter technique. The positioning accuracy of /spl plusmn/4 nm was obtained by optimization of the system.

Projection moiré: using tensor calculus for general geometries of optical setups

Abstract: The projection moire technique enables quantitative measurements of the shape of an opaque curved object surface in space. In contrast to the actual literature, where the interpretation of moire fringes is mostly limited to particular geometrical configurations, we present a strong mathematical tool that makes it possible to accurately analyze more general and complicated geometrical cases. We therefore introduce a mathematical model based on the calculation with projectors and use tensor calculus to deduce the general equations of projection moire. Emphasis is put on relative moire, which is used in most experiments, and on difference moire, which is generally used to calibrate optical systems. The concept of a sensitivity vector, which comes essentially from holographic interferometry, is also introduced. Using a computer-based image processing system, a numerical experimental verification of the obtained theoretical tensor equations is performed. Simultaneously, we describe how to calibrate an optical setup and gain evidence of a few nonlinear effects. This shows which parameters of the setup are of importance and should be carefully controlled. Moreover, we treat some well-known special cases to demonstrate the agreement with the existing literature.

Optical fringe multiplication in moiré interferometry

Abstract: An optical method for multiplication of moire fringes is proposed to increase the sensitivity of moire interferometry The process involves two recording steps In the first step, a traditional moire interferometry setup is used The moire pattern containing carrier fringes and load fringes is recorded onto a glass-based holographic plate The carrier frequency is much lower than that of the original specimen grating The plate is then developed In the second step, the holographic plate, regarded as a distorted specimen grating, is further examined by a similar moire interferometry system The frequency of the second virtual grating is arranged to be 2n times that of the carrier fringes contained in the recorded plate As a result, the load fringes are revealed with a multiplication factor of 2n The interpretation of the optical multiplication method from wave-front interference theory is given and an experiment is conducted

Moire patterns in disparity measurement

Abstract: Calculating disparity between left and right images is an essential operation in stereo vision. The technique proposed in this paper explores the Moire phenomenon for determining the disparity between regions in two images. Moire patterns are obtained when two similar images are superimposed one on another. Any two images that differ in orientation would still match at the fixed point, according to the Brouwer's theorem. When two images are superimposed the concentric Moire rings point to the location of the fixed point. The location of the fixed point gives the disparity.

Apparatus for measuring surface shape

Abstract: PURPOSE:To remove reflections from a grating forming moire fringes. CONSTITUTION:A coherent light from a light source 3 is cast on an object 8 through a grating 7. The cast light is reflected, forming moire fringes at the grating 7. The moire fringes are photographed by a camera 12, and a surface shape of the object 8 is measured from the photographed result. An angle of the grating 7 is properly adjusted so as to prevent the light reflected and diffracted by the grating 7 at that time from entering the photographing camera 12. A light reflected from a protecting cover 8b of the object 8 is distinguishably measured from the reflected/diffracted light from a substrate 8a by rotating a polarizer 10.

Application of high resolution geometric moiré method to fracture problems

Abstract: A high density geometric moire technique has been developed and successfully applied to determine fracture parameters, namely the opening mode stress intensity factor, in both transparent and opaque engineering materials. With the development of this technique the displacement resolution capability of geometric moire has been increased at least twofold, from 0.025 mm to 0.0125 mm. Further development of gratings with line densities higher than 80 line pairs/mm will further bridge the gap which currently exists between the displacement measuring capabilities of geometric and interferometric moire.

Moire based stereo matching technique

Abstract: The technique proposed in this paper explores the Moire phenomenon for determining the disparity between regions in two images. Moire patterns are obtained when two similar images are superimposed one on another. Any two images that differ in orientation would still match at the fixed point, according to the Brouwer's theorem. When two images are superimposed the concentric Moire rings point to the location of the fixed point. The location of the fixed point gives the disparity. Applications of the above technique to stereo vision and video stabilization are reviewed.

Practical method for evaluating the visibility of moire patterns for CRT design

Abstract: The high resolution CRT displays used for computer monitor and high performance TV often produce a pattern of bright and dark stripes on the screen called a moire pattern. The elimination of the moire is an important consideration in the CRT design. The objective of this study is to provide a practical method for estimating and evaluating a moire pattern considering the visibility by the human vision. On the basis of the mathematical model of a moire generation, precise value of the period and the intensity of a moire are calculated from the actual data of the electron beam profile and the transmittance distribution of apertures of the shadow mask. The visibility of the moire is evaluated by plotting the calculation results on the contrast-period plane, which consists of visible and invisible moire pattern regions based on experimental results of the psychological tests. Not only fundamental design parameters such as a shadow mask pitch and a scanning line pitch but also details of an electron beam profile such as a distortion or an asymmetry can be examined. In addition to the analysis, the image simulation of a moire using the image memory is also available.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Frequency-modulated halftone image and formation method

Abstract: PURPOSE: To provide a halftone screen for which object moire is suppressed to the minimum by obtaining halftone dots by locally randomly processing a decision theoretical frequency modulation screen. CONSTITUTION: A memory 310 stores original contone image data inputted from a raster image processor 304. In the memory 320, a halftone pixel value 322 as an output value to a recorder 326 is stored. A screen function generator module 340 is provided with a B ayer matrix 342 and a random processing block 344. By the original B ayer matrix 342 and a random processing in the block 344, a random change screen function value 346 is prepared. A comparator 360 compares the prepared screen function value T346 with the corresponding pixel value P312 of the memory 310. Then, depending on whether a P value is larger or smaller than a T value, halftone values H362 to be '1' (block) or '0' (white) respectively are prepared.

Non-contact solid measurement device

Abstract: PURPOSE:To provide a non-contact solid-measuring device capable of measuring with high accuracy and of facilitating the adjustment work at a low cost. CONSTITUTION:An emission light from a point source array 5 is inputted to a lens 1 via a focusing face 4 and a shading grating 2 and the lens 1 introduces the inputted light to an image-taking face 3. A moire fringes 7 are generated on the image-taking face 3 without adjusting the position strictly. The moire fringes 7 are deformed by a strain of an object to be measured placed on the focusing face 4. The surface strain is measured based on the deformation of the moire fringes.

Method for forming sample image

Abstract: PURPOSE:To realize a method for forming a sample image in which the irregularity information of the sample can be provided with a simple structure, and the irregularity information can be easily provided even when the sample has a smooth surface. CONSTITUTION:When a secondary electron detector 8 is an aggregate of a number of lattice-type detectors, the signal detecting system by a projecting optical system 7 and the detector 8 has an effect equivalent to a lighting system for projecting the lattice onto a sample 4. Thus, Moire fringes can be generated between the lattice-type image projected on the sample 4 and the lattice-type raster on the sample 4 of an electron beam EB. Thus, the moire fringes are displayed on a cathode-ray tube 10, and the irregularity information for the surface of the sample 4 can be precisely grasped from this image.

Analogies between holographic and moire aspherical compensators

Abstract: Computer generated holographic and moire aspherical compensators are frequently regarded as two completely different devices to analyze interferograms. Here we will show that they have more in common than normally thought.