Moiré

In mathematics, physics, and art, a moiré pattern (/mwɑːrˈeɪ/; French: [mwaˈʁe]) 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 are not completely identical, they must be displaced, rotated, etc. or have different, but similar pitch.

Moiré patterns appear in many different situations. In printing, the printed pattern of dots can negatively 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.

The history of the word moiré is complicated. The earliest agreed origin is the Arabic mukhayyar (مُخَيَّر in Arabic, which means chosen), a cloth made from the wool of the Angora goat, from khayyara (خيّر in Arabic), "he chose" (hence "a choice, or excellent, cloth"). It has also been suggested that the Arabic word was formed from the Latin marmoreus, meaning "like marble". By 1570 the word had found its way into English as mohair. This was then adopted into French as mouaire, and by 1660 (in the writings of Samuel Pepys) it had been adopted back into English as moire or moyre. Meanwhile, the French mouaire had mutated into a verb, moirer, meaning "to produce a watered textile by weaving or pressing", which by 1823 had spawned the adjective moiré. 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.

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