Topic
Moiré pattern
About: Moiré pattern is a research topic. Over the lifetime, 1917 publications have been published within this topic receiving 27176 citations. The topic is also known as: moiré fringes & moire pattern.
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22 Jun 2004
TL;DR: The Projected Pattern Correlation (PPC) method as discussed by the authors was proposed to measure the surface velocities of a large area simultaneously, which replace a time consuming point wise scanning as it is necessary in e.g. Laser Doppler Vibrometry.
Abstract: The objective of this paper is the description of the Projected Pattern Correlation method for measuring surface velocities and to present results of a feasibility study. Similar to the Moire technique the local surface velocities of a large area are determined simultaneously, which replace a time consuming point wise scanning as it is necessary in e.g. Laser Doppler Vibrometry. Furthermore, the dynamics of non-periodic processes can be resolved temporally and spatially. In difference to the Moire or grid projection techniques the evaluation step is fast (real-time measurements are possible) more robust and provides a high spatial resolution. The measurement precision is assessed using a simple test arrangement. Vibration measurements are performed on a satellite model structure and a honeycomb sandwich plate.
13 citations
TL;DR: A new optoelectronic system based on a projection unit in which light impinges on a diffractive optical element to produce sinusoidal fringes is proposed for three-dimensional texture measurement, suitable for in situ measurements by nonskilled operators.
Abstract: A new optoelectronic system is proposed for three-dimensional (3D) texture measurement. It is based on a projection unit in which light, coming from a laser diode coupled to an optical fiber, impinges on a diffractive optical element (DOE) to produce sinusoidal fringes. If the projected fringe pattern is viewed at an angle different from the projection angle, the fringe profile is phase-modulated by the 3D object shape. The 3D map information is obtained with the aid of a fringe analyzer based on phase-shifting a synthetic moire pattern, fast Fourier transform (FFT), signal demodulation techniques and a robust and fast phase unwrapping performed by specially developed software. The proposed system is based on simple and low cost equipment; furthermore, it is suitable for in situ measurements by nonskilled operators. Some experimental examples illustrate its performance.
13 citations
TL;DR: Three fringe multiplication methods are proposed which use a digital image processing technique to multiply various interferometric fringes, easy to handle and greatly improve the measurement accuracy.
Abstract: Holographic moire fringes can be multiplied by using diffraction interferometry, an approach which is not applicable to some other interferometric techniques such as geometric moire. Three fringe multiplication methods are proposed which use a digital image processing technique to multiply various interferometric fringes. These methods are easy to handle and greatly improve the measurement accuracy. They enlarge the testing range for applying the interferometric techniques.
13 citations
TL;DR: The proposed method implements a fast way to determine the topography of a surface through a simple experimental setup and develops an iterative procedure to reduce the detuning error introduced by the PCA algorithm.
Abstract: We present a fast phase-shifting shadow moire device for surface topography measurement. In our setup, multiple light sources located at different positions are controlled to illuminate the grating sequentially. Therefore, the phase shift across the field of view shadow moire is introduced by changing the distance between the light source and the camera. Thanks to the necessity for mechanical movement being omitted here, the proposed setup can capture the phase-shifting fringe patterns at a high speed. However, affected by the bias modulation and amplitude modulation of the captured fringe patterns, the phase of interest cannot be demodulated by the standard phase-shifting algorithm directly. Thus the principal component analysis (PCA) demodulation approach is used to extract the wrapped phase map. In addition, we develop an iterative procedure to reduce the detuning error introduced by the PCA algorithm. The proposed method implements a fast way to determine the topography of a surface through a simple experimental setup. It is applied to obtain an external surface of a specimen. Both the simulation results and the experimental results show the validity of the proposed technique.
13 citations
Patent•
27 Feb 1989
TL;DR: In this paper, a plurality of grained screen patterns that are different from each other are stored in a general screen pattern memory and accessed at random in response to an address signal (AGP) generated in a random number generator.
Abstract: A plurality of grained screen patterns that are different from each other are previously stored in a grained screen pattern memory. The grained screen patterns are accessed at random in response to an address signal (AGP) generated in a random number generator. An original image data is compared with the random arrangement of the grained screen patterns for each pixel, to produce a halftone dot image. The halftone dot image thus obtained has no periodic distribution of density, such as a moire.
13 citations