1. A method for image matting based on a hierarchical graph model, comprising: receiving an input image including a plurality of image elements; generating a plurality of matting cells, the generating including converging a subset of image elements of the plurality of image elements toward each other, wherein each cell includes a group of image elements; calculating affinity values for the plurality of matting cells based on the input image; and forming a graph based on the plurality of matting cells and the affinity values, the graph including a plurality of nodes representing the matting cells and a plurality of edges associated with the affinity values of the matting cells; generating a plurality of matting components for the input image by decomposing the graph; and identifying at least one of the matting components belongs to a foreground region of the input image.