Lazy Snapping

"Lazy Snapping," Li, et. al., ACM SIGGRAPH, 2004

The paper presents a coarse-to-fine UI design for image cutout which is the technique of removing an object in an image from the background. There are two steps : (1) object marking (2) boundary editing.
In the first step, user can specify the foreground and background region respectively. Then, the uncertain region can be labeled by calculating the likelihood energy function. In order to get likelihood energy of each region, first cluster the colors in seeds F and B by the K-means method. And compute the minimum distance for each node. Moreover, add a penalty term to specify the gradient effect. Finally, minimize the energy and get the result. To improve the efficiency, apply watershed algorithm on the graph cut formulation to dealt with the segmented regions, and possibly get the reasonable result in a significantly improved speed.
The fine boundary can be adjusted in the second step. But the prior energy is fixed by adding the polygon locations as soft constraints.
In conclusion, they succeed in develop an interactive system to cut out the foreground object from the background in an image. However, they want to do better at the thin and branch structures.