Abstract: Digital matting is the key technology in image processing, video editing and film-making applications. It refers to the problem of extracting the foreground objects in the images or videos accurately, which is an important issue in the field of computer vision. In this paper, the interaction modes for digital matting are introduced firstly. After that, matting techniques are divided into four categories: color sampling based, pixel affinity based, energy function based and machine learning based. Classic algorithms and the latest research progress are presented and analyzed, followed by quantitative and qualitative evaluations of these techniques. Finally, the research progress is summarized and future research directions are suggested.