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{{complex|date=July 2012}}
{{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]]s.
Superimposition of 2D images containing correlated periodic grid structures may produce [[moiré pattern]]s. Superimposition of two correlated layers comprising 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]]
{{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]]s.
Superimposition of 2D images containing correlated periodic grid structures may produce [[moiré pattern]]s. Superimposition of two correlated layers comprising 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]]