Forma, Vol. 6 (No. 1), pp. 9-25, 1991
Original Paper

Properties of Extended Digital a-hull with Applications to Shape Feature Analysis of a Figure Set

Toyofumi Saito, Jun-ichiro Toriwaki, and Shigeki Yokoi

Department of Information Engineering, Faculty of Engineering, Nagoya University, Nagoya 464, Japan

(Received July 24, 1990; Accepted December 3, 1990)

Keywords: a-hull, Fusion, Distance Transformation, Region Extraction

Abstract. The a-hull is a generalization of the convex-hull defined in the continuous space, and its shape can be changed by adjusting the value of the parameter a. In this paper we extend the concept of the a-hull to a set of connected components in a digitized binary picture. The new a-hull called the extended digital a-hull (EDa-hull) is a region which circumscribes the connected component set. We show that the EDa-hull for a<0 can be obtained by employing the distance transformation twice, or by applying the fusion operation which consists of R (=|1/a|) times of erosion followed by R times of dilation. Application of the EDa-hull to a microscope image of tissue section and other examples are shown with the definition of a shape feature parameter.