Moiré pattern

In mathematics, physics, and art, a moiré pattern (UK: /ˈmwɑːr.eɪ/ MWAH-ray; US: /mwɑːˈreɪ/ mwah-RAY; French: ) or moiré fringes are large-scale interference patterns that can be produced when an opaque ruled pattern with transparent gaps is overlaid on another similar pattern. For the moiré interference pattern to appear, the two patterns must not be completely identical, but rather e.g. displaced, rotated or have slightly different pitch. In mathematics, physics, and art, a moiré pattern (UK: /ˈmwɑːr.eɪ/ MWAH-ray; US: /mwɑːˈreɪ/ mwah-RAY; French: ) or moiré fringes are large-scale interference patterns that can be produced when an opaque ruled pattern with transparent gaps is overlaid on another similar pattern. For the moiré interference pattern to appear, the two patterns must not be completely identical, but rather e.g. displaced, rotated or have slightly different pitch. Moiré patterns appear in many different situations. In printing, the printed pattern of dots can interfere with the image. In television and digital photography, a pattern on an object being photographed can interfere with the shape of the light sensors to generate unwanted artifacts. They are also sometimes created deliberately – in micrometers they are used to amplify the effects of very small movements. In physics, its manifestation is the beat phenomenon that occurs in many wave interference conditions. The term originates from moire (moiré in its French adjectival form), a type of textile, traditionally of silk but now also of cotton or synthetic fiber, with a rippled or 'watered' appearance. Moire, or 'watered textile', is made by pressing two layers of the textile when wet. The similar but imperfect spacing of the threads creates a characteristic pattern which remains after the fabric dries. In French, the adjective moiré (in use since at least 1823) derives from the earlier verb moirer, 'to produce a watered textile by weaving or pressing'. Moirer, in turn, is a variation of the word mouaire which is an adoption of the English mohair (in use since at least 1570). Mohair comes from the Arabic mukhayyar (مُخَيَّر, lit. 'chosen'), a cloth made from the wool of the Angora goat. Mukhayyar (مُخَيَّر) descends from khayyara (خيّر, lit. 'he chose'). 'Chosen' is meant in the sense of 'a choice, or excellent, cloth'. It has also been suggested that the Arabic word was formed from the Latin marmoreus, meaning 'like marble'. By 1660 (in the writings of Samuel Pepys), moire (or moyre) had been adopted in English. Moire (pronounced 'mwar') and moiré (pronounced 'mwar-ay') are now used somewhat interchangeably in English, though moire is more often used for the cloth and moiré for the pattern. In the liquid crystal display industry, moiré is often referred to by the Japanese word mura, which roughly translates to 'unevenness; irregularity; lack of uniformity; nonuniformity; inequality.' Moiré patterns are often an artifact of images produced by various digital imaging and computer graphics techniques, for example when scanning a halftone picture or ray tracing a checkered plane (the latter being a special case of aliasing, due to undersampling a fine regular pattern). This can be overcome in texture mapping through the use of mipmapping and anisotropic filtering. The drawing on the upper right shows a moiré pattern. The lines could represent fibers in moiré silk, or lines drawn on paper or on a computer screen. The nonlinear interaction of the optical patterns of lines creates a real and visible pattern of roughly parallel dark and light bands, the moiré pattern, superimposed on the lines.