Digital compositing is the process of assembling multiple images to make a final image, typically for print, motion pictures or screen display.
The basic operation used is known as 'alpha blending', where an opacity value, 'α' is used to control the proportions of two input pixel values that end up a single output pixel.
Consider three pixels;
- a foreground pixel, f
- a background pixel, b
- a composited pixel, c
- α, the opacity value of the foreground pixel. (α=1 for opaque foreground, α=0 for a completely transparent foreground). A monochrome raster image where the pixel values are to be interpreted as alpha values is known as a matte.
- cr = α fr + (1 - α) br
- cg = α fg + (1 - α) bg
- cb = α fb + (1 - α) bb
Should cite Porter-Duff paper
Compositing often also includes scaling, retouching and colour correction of images.
See also: