Alpha compositing

In <a href="/facts/Computer_graphics/lapBE8wv">computer graphics</a>, alpha compositing or alpha blending is the process of combining one image with a background to create the appearance of partial or full <a href="/facts/Transparency_(graphic)/Xnahvu65">transparency</a>. It is often useful to render <a href="/facts/Picture_element/UzwBvXBV">picture elements</a> (pixels) in separate passes or layers and then combine the resulting <a href="/facts/2D_computer_graphics/j6dBxDpX">2D images</a> into a single, final image called the <a href="/facts/Compositing/xGdHadIj">composite</a>. Compositing is used extensively in <a href="/facts/Film/wM3b9Kk3">film</a> when combining <a href="/facts/Computer-generated_imagery/ThJ2gh1X">computer-rendered image</a> elements with <a href="/facts/Live_footage/rRJrwAH5">live footage</a>. Alpha blending is also used in 2D computer graphics to put <a href="/facts/Rasterized/QXfz5t7E">rasterized</a> foreground elements over a background.
In order to combine the picture elements of the images correctly, it is necessary to keep an associated <a href="/facts/Matte_(filmmaking)/oSja3keR">matte</a> 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 <a href="/facts/Blend_modes/8lK8znNX">blend modes</a>, that are used.

Alpha compositing open-in-new

Alpha compositing