Abstract: In this paper, a novel video matting method based on opacity propagation is proposed. It adopts a two-step framework by first segmenting each frame into bilayer and generating trimaps, and then applying matting algorithm to extract the final alpha mattes. In the bilayer segmentation step, an opacity propagation algorithm is used to predict the foreground object in the following frame. It propagates the opacity values of the former frame to the current, and generates an Opacity Map (OM), which is in most cases much more accurate than the previously used Probability Map (PM). OM is used to extract the foreground object by combining it with the graph cut algorithm. And then an accurate trimap is generated by a trimap refinement method based on a Local Gaussian Mixture Model (LGMM). At last, the opacity propagation is again applied to the unknown regions of the trimap to generate the accurate alpha mattes in a temporally coherent way. The experiment results demonstrate the effectiveness of our method.