What is Superimposition?
{{Wiktionary}} In [[graphics]], '''superimposition''' is when an [[image]] or video is put on top of an already-existing image or video. This is usually done to add to the overall image effect or to hide something (such as when a different face is superimposed over the original face in a [[photograph]]). This technique is used in [[cartography]] to produce [[photomaps]] by superimposing [[grid lines]], [[contour line]]s and other linear or textual mapping features over [[Aerial photograph|aerial photographs]]. Superimposition of 2D images containing correlated periodic grid structures may produce [[Moiré pattern|moiré patterns]]. Superimposition of two correlated layers of [[Parallel (geometry)|parallel lines]] or curves may give rise line moiré patterns. The movement of one of the layers results in a faster movement of the line moiré superimposition image. Such [[optical acceleration]] is known as moiré speedup (check for the formulas of optical speedup for curved patterns). When superimposing two identical layers comprising randomly spaced parallel lines, at a small angle or with a small scaling difference [http://switzernet.com/people/emin-gabrielyan/070227-random-line-moire/ random line moiré] patterns, namely line Glass patterns (after Leon Glass, 1969) appear. Similarly, when superimposing two identical layers of randomly scattered dots at a small angle or with a small scaling difference random dot Glass patterns, namely [http://switzernet.com/people/emin-gabrielyan/070212-random-moire/ random dot moiré], appears. When one of the layers embeds [[complex]] shapes, such as sequences of symbols forming a text, and another layer contains parallel lines or curves, the superimposition image may gives rise to magnified shapes, called shape moiré patterns. {{tech-stub}} [[Category:Graphics]] [[Category:Printmaking]]