Showing papers on "Moiré pattern published in 1979"

Phase-locked moiré fringe analysis for automated contouring of diffuse surfaces

Abstract: Phase-locked moire systems have the advantage of rapid data acquisition and accuracy of better than one twentieth of the fringe spacing. In conventional moire systems data acquisition is performed by making a photographic plate and taking measurements from the plate either visually or with a microdensitometer. This is slow, and the accuracy is about one-quarter of the fringe spacing. The phase-locked system is more accurate and permits a more favorable trade-off between accuracy and working depth. The equations governing moire contouring are examined, and the theory of phase-locked moire fringe analysis is presented. The design and operation of the phase-locked moire contouring system are described, and the results of measurements made with the instrument are presented.

Electronic processing of moiré fringes: application to moiré topography and comparison with photogrammetry.

Abstract: Some elements of comparison are given between projection-type moire topography and photogrammetry. The basic mathematics of photogrammetry is used to reconstruct the 3-D shape of the object from the moire pattern. Some particular aspects of the moire method are discussed, and a general methodology is proposed. In connection with this, an optoelectronic technique is described, which measures the moire phase with high resolution and sign determination. The experimental results show that this technique is especially suitable for high accuracy automatic reconstruction of 3-D shapes.

Theoretical aspects and practical applications of Moire topography

Abstract: When a surface is observed at a distance through a parallel line grating which is illuminated by a source of light laterally displaced to the viewing axis, the grating is superimposed on its shadow and this gives rise to a moire fringe pattern. The fringes represent cross-sections of the surface parallel to the grating plane. The principle of the formation of the contour map has been studied assuming a grating represented by a Fourier series, a source of light represented by a 3D intensity distribution and a viewing aperture of finite dimensions. The experimental system used for illumination and observation of the moire fringes consists of an equispaced parallel-lined glass grating and two small light sources positioned symmetrically about the imaging device. The arrangement constitutes a 3D imaging system with an accuracy of the order of 1 mm. The technique has been applied in radiotherapy problems such as the design of contour compensators and the measurement of body contours. Moire patterns have been analysed with the aid of a PDP-8 computer, and have been used to calculate surface areas and volumes such as in breast studies and superficial tumour measurements.

Tunable moiré grating for optical mapping.

Abstract: The use of a moire pattern as a tunable grating is proposed. The moire pattern is created by placing one grating upon another with a varying angle between them. A demonstration of the use of this tunable grating for moire mapping and a discussion of the limitations and possible applications of this method are given.

Moiré interferometry with white light.

Abstract: While high-sensitivity moire interferometry requires monochromatic light, an auxiliary compensator grating removes the requirement. Experimental verification utilized white light for moire interference of sensitivity 0.833 μm/fringe. Configurations readily amenable to compensation include moire fringe multiplication by even factors and the minimum-deviation arrangement. Chromatic compensation is effective with virtual reference gratings as well as real reference gratings; in both cases the moire interference system becomes achromatic. Compensation provides the special quality of nearly zero phase difference—an actual range of ±π—between interfering beams. Potential applications include use of electrical spark light sources for high-sensitivity dynamic moire photography.

Moiré depth contouring

Abstract: Techniques to generate depth profiles of a surface by means of moire fringes have become well known in modern optics. Different mathematical theories of moire depth contouring have been developed using either communication theory or geometric ray tracing. For the oblique shadow method it is shown that these theories can be unified in a closed mathematical analysis. The analysis is extended to the case of various media with different refractive indexes covering the surface of interest.

Multipurpose Optical Moire Processor

Abstract: A multipurpose optical moire processor is described whereby one can introduce mismatches fringes, perform fringe multiplication and shifting, and separate u- and v-field isothetics. These functions can be done individually, sequentially, or simultaneously.

Halftone screen techniques for photographic film response shaping with application to optical processing of medical x-ray images.

Abstract: Optical image processing is notoriously sensitive to nonlinearities in the input medium; many otherwise successful optical processors fail to perform adequately outside the laboratory environment because of this problem. The usual solutions to the problem-use of special photographic emulsions, developers, and even preexposure (bias)-severely limit the applicability of many optical processing schemes and may also degrade the SNR of the input image. We present several methods, all using halftone screens, to obtain proper response from the input photographic film. We then demonstrate one particular method, both theoretically and experimentally, as applied to x-ray recording of coded images that are to be used as input for an optical transaxial tomography processor.

Evaluation of a moiré imaging system.

Abstract: Moire fringe techniques can be used to measure surface topography. The factors that affect the formation of the fringes have been assessed theoretically by developing models of gratings and light sources of finite dimensions. In this way the effect of parameters such as the intensity distribution of the light source, the viewing aperture function, the lateral displacement of the source relative to the viewing axis, the viewing distance, the grating spacing and grating ratio have been evaluated. Other factors, related to the physical properties and geometry of the reflecting surface, are also investigated. Suggestions are made for the design of an optimum Moire imaging system.

Photogrammetric Application Of Moire Fringes Produced With A Parallel Beam Of Light

Abstract: The use of moire interference fringes in biostereometrical applications has the advantage that contour fringes on the surface of an object are visible to the unaided eye and that these fringes may be recorded photographically. The movement of such fringes as would accompany the motion of the human body can be recorded by movie or video camera when the fringes are used to study human subjects. One of the limitations of this moire method using noncollimated light is that the value of the contour interval increases with the increase of the order number of the fringes as counted from the grating. To overcome this limitation, a new moire technique using parallel light has been developed. An optical system, which includes a field lens, provides the parallel light which makes it possible to obtain equal valued contour intervals, independent of fringe order. Any desired contour interval is obtained by choosing a grating with suitable pitch and/or an appropriate angle of incidence for the parallel light at the grating. Analogue data from the moire pattern is automatically fed into the central processing unit of a computer by means of a TV camera and an A/D converter. Examples of the line printer output of this conversion system are given.

Random phase plate for horogram recording

Abstract: PURPOSE:To eliminate the Moire and low frequency noises, when a hologram reproducing image is picked up by a TV camera, by making the positions of the separated units of a phase plate so that the phase changes of the respective units are made constant

Observing method of contour moire fringes

Abstract: PURPOSE:To obtain various contour moire fringes according to applications at the reproducing by using two reference grating respectively independently at the recording and reproducing.

Computerized analysis of moiré contours applied to eardrum shape measurements

Abstract: Khanna and Tonndorf have used moire topography to study the resting shape of the eardrum and the effects of static pressures [J. Acoust. Soc. Am. 57, S72 (1975} and 58, S88 (1975)]. They have recently modified their apparatus so as to remove the parallel grating image that had been superimposed on the moire isotathmic (constant‐depth) contours. By simplifying the pattern recognition problem, this has made it feasible to develop a semiautomatic method of analyzing the data. An interactive computerized image‐processing system is used to identify and extract the contours from the photographic image. An interactive computer‐graphics system is then used for computing shape profiles, volumes, static displacements, etc. and for preparing the shape data for use in a finite‐element model of the eardrum. [Work supported by Medical Research Council of Canada and Macdonald Stewart Foundation.]

Moire Contouring And Applications To Highspeed Photography

Abstract: The localization of Moire fringes is studied theoretically and experimentally from the viewpoint of practical usage in Moire contouring.Introducing the concept of fringes localization verifies the phenomenon that Moire fringes do not always exist on the surface of the object. When this phenomenon is taken into considerations, the optical setup is constructed appropriately and Moire contouring reveals its validity. Some examples are presented including one application to highspeed photography.© (1979) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Measuring and processing method of moire fringes

Abstract: PURPOSE:To make judgement of 3-dimensional undulation relations, etc. of two objects by moving moire interference fringes to the position where two sets of projection gratings have been relatively moved to form plural differential moire fringes and displaying these in different colors, brightnesses, codes, etc. CONSTITUTION:When objects 3, 4 are projected from grating projectors 1, 2 via deformed gratings 5, 6, the moire interference fringe patterns are formed according to the undulations of the objects and are picked up in image pickup devices 7, 8. When the fringe pattern having been picked up by the device 8 via grating movers 14, 15 is moved to the position of the case when the relative distance between the gratings 5, 6 is changed and is processed with differential moire fringe generators 11 thru 13, then plural sets of differential moire fringes 18 thru 20 are formed. When these differential moire fringes 18 thru 20 are displayed in different colors, brightnesses, codes, etc. in a display device 21 and the various movements are controlled with the devices 14, 15, the differential moire fringes discriminated by the colors, etc. move on the device 11 and the 3-dimensional undulation relations between the two objects may be readily discriminated. In a similar manner, the discrimination of the change of the 3-dimensional undulations of one object with time may be accomplished.

Moire Topography As A New Means Of The Three Dimensional Measurement

Abstract: The properties of moire fringes and their applications to the three dimensional measurements will be reported. The three types of typical techniques of the moire topography, an extension of the shadow moire technique which forms the basic method of the moire topography, the projection type, and the grating hologram type will be explaned respectively, putting stress on the merits and the demerits of each method. A brief explanation on the modern trend to introduce the TV techniques to the moire topography will be also made.© (1979) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A dynamic moiré method for deformation measurement of curved surfaces

Abstract: A simple method is proposed for obtaining moire patterns, and information is given on the deformation of curved surfaces. The experimental arrangement is based on the projection-moire principle and consists of a projector and a camera. A transparent object, e.g., a shell with line gratings, is projected onto the focal plane of this projector and superposed there with a reference grating which describes the undeformed state of the curved surface in the form of a transparent picture. Moire patterns are obtained by simultaneously superposing the projected line grating in the shell's deformed state and the reference grating. They present a general picture of the behavior of the object during loading, such as during impact if the patterns are recorded with a high-speed camera.

Moire fringe measuring method

Abstract: PURPOSE:To enable order calculation of moire fringes to be automatcally performed with a computer by using a projection grating in which periodes are made imperfect. CONSTITUTION:At the time of projecting a projection gratiang 3 to an object 5 by the ligh of a spot ligh source 1 and receiving this with the image pickup unit, etc. disposed in the position of an image pickup screen 7, an intermittently toothed grating in which the width of part of slits is made larger is used as the width of part of slits is made larger is used as the projection grating 3. Then, the deformed grating image in which portions are dropped ou is observed on the case when the projection grating in which shiel areas and transmission aras are perfectly periodical is projected to the object 5. Hence, if the deformed grating images are inputted to a computer as binary signals, the positions where the deformed grating images have dropped out may be automatically detected from the considerale differences between the deformed gratings and from the position information thereof, the distance up to the object 5 maq be computed and the order of te moire fringe A' corresponding to that point may also be determined.