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.

Investigations of moiré artifacts induced by flux fluctuations in X-ray dark-field imaging

Abstract: X-ray dark-field imaging using a grating interferometer has shown potential benefits for a variety of applications in recent years. X-ray dark-field image is commonly retrieved by using discrete Fourier transform from the acquired phase-stepping data. The retrieval process assumes a constant phase step size and a constant flux for each stepped grating position. However, stepping errors and flux fluctuations inevitably occur due to external vibrations and/or thermal drift during data acquisition. Previous studies have shown that those influences introduce errors in the acquired phase-stepping data, which cause obvious moiré artifacts in the retrieved refraction image. This work investigates moiré artifacts in X-ray dark-field imaging as a result of flux fluctuations. For the retrieved mean intensity, amplitude, visibility and dark-field images, the dependence of moiré artifacts on flux fluctuation factors is theoretically derived respectively by using a first-order Taylor series expansion. Results of synchrotron radiation experiments verify the validity of derived analytical formulas. The spatial frequency characteristics of moiré artifacts are analyzed and compared to those induced by phase-stepping errors. It’s illustrated that moiré artifacts can be estimated by a weighted mean of flux fluctuation factors, with the weighting factors dependent on the moiré phase and different greatly for each retrieved image. Furthermore, moiré artifacts can even be affected by object’s features not displayed in the particular contrast. These results can be used to interpret image correctly, identify sources of moiré artifacts, and develop dedicated algorithms to remove moiré artefacts in the retrieved multi-contrast images.

Analysis of colour moiré phenomenon in colour space

Abstract: Moire topographic technique is widely used for three-dimensional surface reconstruction. One of the main problems is determination of the absolute order of a fringe for finding the depth difference between two points in moire patterns, i. e. convex and concave surfaces distinction. Most solutions of the problem are very complicated; also they usually require several moire images. Application of colour-encoded gratings in projection moire method allows solving the problem simply and quickly. The authors analyze the information that contains in colour moire fringes and estimate its effectiveness. With this purpose device independent simulations for colour formation of one moire fringe in colour space by different conditions were made.

Method for removing a moire pattern in a three dimensional image display apparatus using a complete parallax for crossing an image display panel and a complete parallax providing device with a predetermined angle

Abstract: PURPOSE: A method for removing a moire pattern in a three dimensional image display apparatus using a complete parallax is provided to cross an image display panel and a complete parallax providing device with a predetermined angle, thereby making a period or a pitch of the moire pattern smaller than a size capable of distinguishing through an optical resolution of a viewer's naked eye. CONSTITUTION: When the first and second grid plates(50,60) are superposed with each other without an interval, an interference pattern, that is, a moire pattern(70) is displayed repeatedly with a predetermined period. The identical interference patterns(72) appear at the regions superposed with the first and third line lattices(40,44) and the second and fourth line lattices(42,46). The second grid plate is rotated with a predetermined angle. The first grid plate is formed by the first and third line lattices and the second grid plate is formed by the second and fourth line lattices. One first square grid(G1) corresponds to one pixel and one second square grid(G2) corresponds to one first square grid.

Moiré deflectometry under incoherent illumination: 3D profiler for specular surfaces

Abstract: We present a novel method for measuring a curved specular surface profile, which is the moire deflectometry under incoherent (white light) illumination. In our proposed system, moire is produced by a superposition of two pairs of Ronchi gratings to obtain orthogonal components of a normal vector on a surface under test. The grating pair was moved along an axis perpendicular to the grating plane to modulate a spatial frequency of the moire. The moire is reflected by a specular object, then observed with a calibrated stereo camera. Normal vector distribution of the tested surface was measured by analysis of intensity oscillations captured by the stereo camera as a function of the position of the moved grating. A surface profile was reconstructed by an integration calculation. We successfully measured surface profiles of deeply curved mirrors with the curvature from -20 to 20 m -1 by our system. Moreover, part of a miniature vehicle body, which has a complex curved specular surface, was also measured. Additionally, we theoretically and experimentally studied a measurable angle variation of the normal vector on the tested surface by our measurement system. We found that our system can allow to measure the angle deviation of 0.05 deg of the normal vector. This method has no ambiguity of slope and height measurements which is appeared in conventional deflectmetric metrologies. Furthermore, our proposed system only needs a single step calibration. Hence, the methodology we proposed has a potential to be developed into a 3D profiler for complex specular surfaces.