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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2 citations
TL;DR: In this article, the displacement field is measured with a random noise level of less than 0.3?m and by using a high-speed camera, a framing speed of 1 million frames/s is achieved.
Abstract: A moire method for dynamic in-plane displacement measurement is used with the purpose of studying carbon fiber/epoxy composite specimens under tensile dynamic load. The displacement field is measured with a random noise level of less than 0.3 ?m and by using a high-speed camera, a framing speed of 1 million frames/s is achieved. Cracks propagating at speeds of 2000 m/s have been observed. To evaluate strain accurately from the displacement fields, a calibration for distortion in the high-speed image converter camera must be made. A method to measure the variable magnifications in the different frame areas of the camera back is described.
2 citations
02 Sep 1992
TL;DR: In this article, the use of a projection moire system to test the surface shape of an injection molded f/0.1 parabolic reflector is presented, and some alignment errors associated with the system and how to correct them are presented.
Abstract: Testing injection molded aspheres, with large deviations from spherical is difficult. One solution is to use a long wavelength interferometer, such as an infrared interferometer. Another solution is to use moire. This paper presents the use of a projection moire system to test the surface shape of an injection molded f/0.1 parabolic reflector. The theory of moire and its effective wavelength is presented. A projection system is constructed and data taken for a reflector is shown. Finally, some alignment errors associated with the system and how to correct them is presented.
2 citations
TL;DR: A new type of moiré pattern caused by inhomogeneous detector sensitivity in computed tomography is reported, which induces a noise-like pattern or a subtle texture in the reconstructed images.
Abstract: We report a new type of moire pattern caused by inhomogeneous detector sensitivity in computed tomography. Defects in one or a few detector bins or miscalibrated detectors induce well-known ring artifacts. When detector sensitivity is not homogenous over all detector bins, these ring artifacts occur everywhere as distributed rings in reconstructed images and may cause a moire pattern when combined with insufficient view sampling, which induces a noise-like pattern or a subtle texture in the reconstructed images. Complete correction of the inhomogeneity in detectors can remove the pattern and improve image quality. This paper describes several properties of moire patterns caused by detector sensitivity inhomogeneity.
2 citations
TL;DR: In this article , the authors proposed to combine phase and amplitude modulated (DW-PAM) fringes, which reduced the number of phase-shifted fringes by half and reduced the signal-to-noise ratio (SNR).
Abstract: Fringe projection profilometry (FPP) is a well-known technique for digitizing solids. In FPP, straight fringes are projected over a digitizing solid, and a digital camera grabs the projected fringes. The sensitivity of FPP depends on the spatial frequency of the projected fringes. The projected fringes as seen by the camera are phase modulated by the surface of the digitizing object; the demodulated phase is usually wrapped. If the digitizing object has discontinuities larger than the fringe period, the phase jumps are lost. To preserve large phase discontinuities, one must use very low spatial frequency (low-sensitivity) fringes. The drawback of low-sensitivity FPP is that the demodulated phase has low signal-to-noise ratio (SNR). Much higher SNR is obtained by projecting shorter wavelength, at the cost of obtaining wrapped phase. A way out of this problem is to use dual-wavelength FPP (DW-FPP). In DW-FPP, two sets of projected fringes are used, one with long wavelength and another with shorter wavelength. Due to harmonics and gamma distortion, in DW-FPP, one usually needs four phase-shifted fringes for each sensitivity. Here we are proposing to combine the two sensitivities simultaneously, one coded in phase (PM) and the other coded in amplitude (AM), in order to obtain phase and amplitude modulated (DW-PAM) fringes. The low-sensitivity phase is coded as AM of the DW-PAM fringes. The main advantage of DW-PAM fringes is that one reduces the number of phase-shifted fringes by half: instead of using eight phase-shifted fringes (four for low and four for high sensitivities), one would need only four DW-PAM fringes. Of course, if one wants to increase the harmonic rejection of the recovered phase, one may use a higher order phase-shifting algorithm (PSA).
2 citations