Perimeter边界长度. 计算方式跟边界的表示方式有关Area包含的点的个数Compactness两种常用的计算方式\(\frac {perimeter^2}{area}\).circularity ratio = \(\frac {\text{area}}{\text{area of bounding circle}}\)直觉的理解:convex deficiency/hole, 越多/越大, 紧凑程度越低.Scale insensitive.