Editing Alpha compositing (section)

{{short description|Operation in computer graphics}}

[[Image:Hue alpha falloff.svg|thumb|A [[Visible spectrum|color spectrum]] image with an alpha channel that falls off to zero at its base, where it is blended with the background color.]]

In [[computer graphics]], '''alpha compositing''' or '''alpha blending''' is the process of combining one image with a background to create the appearance of partial or full [[Transparency (graphic)|transparency]].<ref>{{Cite web|title=Definition of alpha blending|url=https://www.pcmag.com/encyclopedia/term/alpha-blending|access-date=2021-08-07|website=PCMAG|language=en}}</ref> It is often useful to render [[picture element]]s (pixels) in separate passes or layers and then combine the resulting [[2D computer graphics|2D images]] into a single, final image called the [[compositing|composite]]. Compositing is used extensively in [[film]] when combining [[Computer-generated imagery|computer-rendered image]] elements with [[live footage]]. Alpha blending is also used in 2D computer graphics to put [[rasterized]] foreground elements over a background.

In order to combine the picture elements of the images correctly, it is necessary to keep an associated ''[[matte (filmmaking)|matte]]'' for each element in addition to its color. This matte layer contains the coverage information—the shape of the geometry being drawn—making it possible to distinguish between parts of the image where something was drawn and parts that are empty.

Although the most basic operation of combining two images is to put one over the other, there are many operations, or [[blend modes]], that are used.