Superimposition is the placement of one thing over another, typically so that both are still evident. Superimpositions are often related to the mathematical procedure of superposition.

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 Music track, tracks that have been pre-recorded are then played back and monitored, while simultaneously recording new, doubled, or augmented tracks onto o ...

) 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.

2D images

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 the data, as in design and manufa ...

, superimposition is the placement of an

image An image or picture is a visual representation. An image can be Two-dimensional space, two-dimensional, such as a drawing, painting, or photograph, or Three-dimensional space, three-dimensional, such as a carving or sculpture. Images may be di ...

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, or more generically referred to as an ''image'' or ''picture'') is an image created by light falling on a photosensitivity, photosensitive surface, usually photographic film or an electronic image sensor. Th ...

). 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 wave interference, interference patterns that can be produced when a partially opaque grating, ruled pattern with transparent gaps is overlaid on ano ...

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 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 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 patterns.

Cartography

This technique is used in

cartography Cartography (; from , '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 imagined reality) can ...

to produce photomaps by superimposing grid lines,

contour line A contour line (also isoline, isopleth, isoquant or isarithm) of a Function of several real variables, 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 ...

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 ...

Forensics

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

Audio

2D images

Cartography

Forensics

See also

References

Further reading