Abstract: Digital matting is a new technology of extracting the foreground from the background.It is meant to automatically extract all the other parts of the foreground objects based on a few user-specified parts.In this paper,its historical development is at first outlined,followed by a detailed review on the main matting technologies,including blue screen matting,natural image matting,as well as some extended technologies of matting on image,such as environment matting,shadow matting,and video matting.In the end,the currently encountered main difficulties in the field and some promising future directions are listed.