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Superimposition is the placement of one thing over another, typically so that both are still evident.


Graphics

In
graphics Graphics () are visual images or designs on some surface, such as a wall, canvas, screen, paper, or stone, to inform, illustrate, or entertain. In contemporary usage, it includes a pictorial representation of data, as in design and manufacture ...
, superimposition is the placement of an
image An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...
or video on top of an already-existing image or video, usually to add to the overall image effect, but also sometimes to conceal something (such as when a different face is superimposed over the original face in a
photograph A photograph (also known as a photo, image, or picture) is an image created by light falling on a photosensitive surface, usually photographic film or an electronic image sensor, such as a CCD or a CMOS chip. Most photographs are now create ...
).


Cartography

This technique is used in
cartography Cartography (; from grc, χάρτης , "papyrus, sheet of paper, map"; and , "write") is the study and practice of making and using maps. Combining science, aesthetics and technique, cartography builds on the premise that reality (or an im ...
to produce photomaps by superimposing grid lines,
contour line A contour line (also isoline, isopleth, or isarithm) of a function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value. It is a plane section of the three-dimensional grap ...
s and other linear or textual mapping features over
aerial photograph Aerial photography (or airborne imagery) is the taking of photographs from an aircraft or other airborne platforms. When taking motion pictures, it is also known as aerial videography. Platforms for aerial photography include fixed-wing ai ...
s.


2D images

Superimposition of two-dimensional images containing correlated periodic grid structures may produce
moiré pattern In mathematics, physics, and art, moiré patterns ( , , ) 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 ...
s. Superimposition of two correlated layers comprising parallel lines or curves may give rise
line moiré Line moiré is one type of moiré pattern; a pattern that appears when superposing two transparent layers containing correlated opaque patterns. Line moiré is the case when the superposed patterns comprise straight or curved lines. When moving the ...
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 random line moiré patterns, namely line Glass patterns (after
Leon Glass Leon Glass (born 1943) is an American scientist who has studied various aspects of the application of mathematical and physical methods to biology, with special interest in vision, cardiac arrhythmia, and genetic networks. Biography Leon Gla ...
, 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 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 give rise to magnified shapes, called
shape moiré Shape moiré is one type of moiré patterns demonstrating the phenomenon of moiré magnification. 1D shape moiré is the particular simplified case of 2D shape moiré. One-dimensional patterns may appear when superimposing an opaque layer containin ...
patterns.


Forensics

Photographic superimposition is a forensic technique. This can include craniofacial superimpositioning, which compares skulls of the deceased with images of them through the overlap of photographs.


Audio

Superimposition (SI) during sound recording and reproduction (commonly called
overdubbing Overdubbing (also known as layering) is a technique used in audio recording in which audio tracks that have been pre-recorded are then played back and monitored, while simultaneously recording new, doubled, or augmented tracks onto one or more av ...
) is the process of adding new sounds over existing without completely erasing or masking the existing sound. Some reel-to-reel tape recorders of the mid 20th century provided crude superimposition facilities that were implemented by killing the high-frequency AC feed to the erase head while recording as normal via the read-write head.


See also

*
Forensic facial reconstruction Forensic facial reconstruction (or forensic facial approximation) is the process of recreating the face of an individual (whose identity is often not known) from their skeletal remains through an amalgamation of artistry, anthropology, osteol ...


References


Further reading

*Natale, Simone. (2012
A Short History of Superimposition: From Spirit Photography to Early Cinema.
''Early Popular Visual Culture'' 10.2: 125–45. {{doi, 10.1080/17460654.2012.664745 Printmaking Printing Artistic techniques Cartography