In
graphics, superimposition is the placement of an
image 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). Superimposition of two-dimensional images containing correlated periodic grid structures may produce
moiré patterns. 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 to produce
photomaps by superimposing grid lines,
contour lines and other linear or textual mapping features over
aerial photographs.
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. == See also ==