The process of electronically creating a composite image by replacing portions of one image with another. One common, if rudimentary, form of this process is chroma-keying, where a particular colour in the foreground scene (usually blue) is replaced by the background scene. Electronic matting is commonly used to create composite images where actors appear to be in places other than where they are being shot.

It generally requires more chroma resolution than vision does, causing contribution schemes to be different than distribution schemes. While there is a great deal of debate about the value of ATV to viewers, there does not appear to be any dispute that HDEP can perform matting faster and better than almost any other moving image medium.