Contour scanning based Euclidean distance transformation (EDT) is a fast and complete EDT algorithm and achieves the optimum complexity. But it needs to search all contour regions

so the computation is not optimal. To overcome this disadvantage

an EDT algorithm based on contour hierarchical scanning was proposed. First

reclassifying pixels of the binary image according contour character of central pixel is needed. Second

according the spatial relationship between contour region pixel and central pixel

searching contour region of central pixel hierarchically is the main step to reduce the computation. Finally

we use the proposed terminal condition ends the searching. Theoretically

the proposed algorithm maintains the optimum complexity and reduces the computation. Likewise

the experiments showed that the proposed algorithm can obtain the Euclidean distance images exactly and reduce the calculation time cost.