superimposition

Superimposition is the act of placing one object over another, such that both are visible or the combination conveys more information than either would alone. In photography and visual arts, it refers to overlaying images through transparency, masking, or digital compositing to create a single image that contains multiple scenes or elements. In printing, design, and cinema, layering techniques and methods like double exposure are used to merge generations of imagery into one frame.

In science and engineering, the term is related to the principle of superposition. In linear systems, the overall response to multiple stimuli equals the sum of the responses to each stimulus. This underpins analyses in acoustics, electromagnetism, structural mechanics, and, in quantum mechanics, the idea that a system can exist in a superposition of states.

In geology and paleontology, the principle of superposition states that in an undeformed sequence of sedimentary rocks, older layers lie below younger ones. This provides a basis for relative dating and reconstructing the geological history of an area. The concept also informs stratigraphic correlation and interpretation of past environments.

In medical imaging and computer vision, superimposition is used to overlay anatomical images with labels or to fuse images from different modalities, such as CT and MRI, to aid diagnosis, planning, and guidance. It is also employed in forensics and documentation to compare or authenticate visual evidence, with careful notes about any alterations or composites.

See also: overlay, image fusion, double exposure, stacking.