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.

Method of moire-metrical testing of optical imaging systems

Abstract: A method for testing optical imaging systems by the use of moire stripes, wherein two copies of an optical grating are made and simultaneously illuminated to produce a moire pattern which is a measure of the distortion of the imaging system. In a first step an original grating is transferred by a light beam as a contact copy onto a substrate. In a second step, the imaging system to be tested copies the original grating for a second time onto the substrate, except that the second grating copy is rotated slightly with respect to the first grating copy. The points of intersection of the two superimposed gratings produce moire stripes when illuminated, the positions of the stripes being calculated precisely with the assumption that ideal gratings were used. If the imaging system to be tested shows distortions, the position of the moire stripes that are observed will not correspond to these calculated positions. The deviation therefrom is a measure of the imaging system errors.

Reduction of a grid moiré pattern by integrating a carbon-interspaced high precision x-ray grid with a digital radiographic detector.

Abstract: The stationary grid commonly used with a digital x-ray detector causes a moire interference pattern due to the inadequate sampling of the grid shadows by the detector pixels. There are limitations with the previous methods used to remove the moire such as imperfect electromagnetic interference shielding and the loss of image information. A new method is proposed for removing the moire pattern by integrating a carbon-interspaced high precision x-ray grid with high grid line uniformity with the detector for frequency matching. The grid was aligned to the detector by translating and rotating the x-ray grid with respect to the detector using microcontrolled alignment mechanism. The gap between the grid and the detector surface was adjusted with micrometer precision to precisely match the projected grid line pitch to the detector pixel pitch. Considering the magnification of the grid shadows on the detector plane, the grids were manufactured such that the grid line frequency was slightly higher than the detector sampling frequency. This study examined the factors that affect the moire pattern, particularly the line frequency and displacement. The frequency of the moire pattern was found to be sensitive to the angular displacement of the grid with respect to the detector while the horizontal translation alters the phase but not the moire frequency. The frequency of the moire pattern also decreased with decreasing difference in frequency between the grid and the detector, and a moire-freeimage was produced after complete matching for a given source to detector distance. The image quality factors including the contrast, signal-to-noise ratio and uniformity in the images with and without the moire pattern were investigated.

Non-orthogonal screen and its application in moire-free halftoning

Abstract: In color reproduction, the most troublesome moire pattern is the second-order moire, or the three-color moire, usually produced by mixing of cyan, magenta and black halftone outputs. A classical 3-color zero-moire solution is using three identical cluster halftone screens with different rotations: 15, 45 and 75°, respectively. However, for most digital printing devices, the size and shape of halftone screens are constrained by the "digital grid", which defines the locations of printed dots; and therefore, an exact 15 or 75° rotation of a cluster screen is impossible. Although there are many alternative approaches for moire-free color halftoning, most of them only provide approximate solutions and/or have a tendency to generate additional artifacts associated with halftone outputs. The difficulty to achieve moire-free color halftoning is greatly relieved by using non-orthogonal halftone screens, i.e., screens in general parallelogram shapes. In this paper, a general condition for 3-color zero-moire solutions is derived. A procedure using integer equations to search moire-free solutions for different applications is also described.

Contouring of diffused objects using lensless Fourier transform digital moiré holography

Abstract: A method is proposed for contouring of diffused objects using digital holographic moire interferometry in lensless Fourier transform configuration. Fringe projection moire technique combined with digital double-exposure holography produces the contours in this method. Two digital holograms of a 10 mm aluminum alloy cube are recorded by tilting the illumination angle slightly between exposures, and a third one is recorded by translating the detector a little laterally with the final illumination angle unchanged. Upon numerical processing of the first two holograms, a plane parallel fringe system seems to be projected onto the object. This fringe system can be referred to as the modified grid. Processing of the second and the third hologram results in another grid, the reference grid. In effect, processing of the first and the third hologram combines the modified and the reference grids to produce the moire contour fringes. The range of contour intervals obtained remains between 2.73 and 0.38 mm with seven different contours in between. The present method can measure details of a great variety of sizes on objects of large dimensional range. Deviations in the measured contour intervals from the theoretically calculated values are found to be within 12%–18%. This seems to be because of the deviation in the present experimental geometry from the ideal theoretical configuration, the hologram digitization, and the particular reconstruction algorithm used in the present experimental arrangement.

Moiré gauging by projected interference fringes

Abstract: The formation of Moire patterns by doubly exposed photographs of projected interference fringes is analysed in detail. The possible applications of these patterns for the measurement of surface deformation and vibration, phase object visualization and height contouring are examined theoretically and experimentally. The described methods are closely related to holographic techniques, but they are usually simpler and applicable in unfavourable environments.