The Chan and Vese (C-V) model using one level set function can only represent one object and one background by the sign of the function and can not express the multiple junctions of multiple objects.To deal with the problem

a tree-like multiphase level set algorithm for segmentation based on the C-V model is proposed whose basic idea is changing the background in the image so that the level set function will detect new object in the observed image.A key technique

called the technique of painting background

is proposed following the theory of simultaneous brightness contrast.Moreover

a hieranchical procedure of the proposed algorithm using multiple level sets is developed for multiphase segmentation (

n

-1 level sets for

n

phases

n

＞1).Experimental results show that the proposed algorithm can represent multiple junctions of regions (

n

-phase segmentation for at most representing n junctions) and detect multiple objects

(n

-phase segmentation for

n

-1 objects).Also

the algorithm is especially effective for images which have sub-objects in the object region.