1. A method, comprising: extracting visual features of a face portrayed in an image, the visual features including a facial shadow that represents three-dimensional information of the face; assigning pixels of the facial shadow into clusters according to an attribute; for each cluster in the facial shadow, selecting a mean color of a corresponding cluster as a representative color of the corresponding cluster; propagating each representative color across all the pixels of the corresponding cluster in the facial shadow; and recombining the visual features to form a cartoon of the face.